摘要:

Crystal structures and magnetic properties of acid–base molecular complexes, (p-pyridyl nitronylnitroxide)2X (X=hydroquinone, fumaric acid and squaric acid) Takeo Otsuka,a Tsunehisa Okuno,a Kunio Awaga*,a,c and Tamotsu Inabeb aDepartment of Basic Science, Graduate School of Arts and Sciences, T he University of T okyo, Komaba,Meguro, T okyo 153, Japan bDivision of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060, Japan cStructure and T ransformation, PRESTO, Japan Science and T echnology Corporation (JST), Japan The reactions of 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide (or p-pyridyl nitronylnitroxide, abbreviated as p-PYNN) with the three dibasic organic acids, X [=fumaric acid (FA), squaric acid (SA) and hydroquinone (HQ)], result in the formation of hydrogen-bonding complexes of (p-PYNN)2 X composition.In their crystals, the organic acids make selective hydrogen bonds to the two kinds of hydrogen-bond accepting sites in p-PYNN; (a) the oxygen atom in the NO group and (b) the nitrogen atom of the pyridyl ring. p-PYNN2 HQ crystallizes in the monoclinic P21/n space group. The HQ molecule bridges two p-PYNNs, and selects site (a) in p-PYNN as the hydrogen bond acceptor [i.e.( p- PYNN)NO HO(HQ)OH ON( p-PYNN)]. p-PYNN2 FA crystallizes in the monoclinic P21/n space group. The FA molecule connects two p-PYNN molecules with an intermolecular hydrogen bond to site (b) [( p- PYNN)N HO(FA)OH N(p-PYNN)]. The 251 compound of p-PYNN and SA crystallizes with the crystal solvent, 1,4- dioxane (abbreviated as diox), in the formula for p-PYNN2 SA diox.The crystal belongs to the triclinic P19 space group. The SA molecule occupies the space between two p-PYNNs, making contact with site (b), as FA does in the p-PYNN2 FA crystal. However the structure of SA indicates that it is a dianion in which the two protons are missing and, thus, the hydrogen bond is ionic [(p-PYNN)NH+ O-(SA)O- H+N(p-PYNN)].The selectivity and features of the hydrogen bonds can be qualitatively understood in terms of competition between the electrostatic and charge-transfer terms in the hydrogen-bonding energy, which is governed by the acidity of the organic acids and the proton accepting abilities of the two sites in p-PYNN.The three molecular compounds exhibited diVerent antiferromagnetic properties, which depend on the mutual arrangement of p- PYNN in the crystals. The intermolecular interactions were interpreted based on the McConnell’s spin polarization mechanism. It is widely accepted that hydrogen bonding can influence intermolecular arrangements in the condensed state containing organic molecules and recently, this has been recognised as a key factor in supramolecular chemistry1 for designing and synthesizing molecular aggregates with fundamental structural, symmetry, topology, and network properties, and for applications,2 such as non-linear optics, ferromagnetism, ferroelectricity, liquid crystals, and electronics.Hydrogen bonding is not only the main factor in determining solid state structures but is also the microscopic origin of physical properties.3 It is important to study the patterns, topology, selectivity, and the strength of hydrogen bonds, that are dependent on the hydrogen-bonding abilities of organic functional groups and on the steric (size and shape) eVects of molecules.While most research has been based on the measurement of solution association constants under equilibrium conditions,4 extraction of the hydrogen-bonding patterns from a wide variety of crystallographic data was performed by Etter et al.5 Crystallographic studies are advantageous in the analysis of hydrogen-bond selectivity in complex systems such as the 2-aminopyrimidinecarboxylic acid compounds, which involve multiple hydrogen bonds.5 In the field of molecular magnetic materials, the idea of making use of intermolecular hydrogen bonds to get ferromagnetic intermolecular interactions, has been tested by Veciana6 and Sugawara7 et al.In addition, we have observed the coexistence of organic radicals and naked protons in the solid state: the reaction of 2-(3-pyridyl)- or 2-(4-pyridyl)- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide (abbreviated as m- or p-PYNN, respectively) and HBr gas leads to the 251 complex, (m-PYNN)2 HBr or (p-PYNN)2 HBr.8 Although single crystals were not obtained, IR spectra strongly indicated proton sharing between the two pyridyl rings, i.e.an intermolecular [NHN]+ hydrogen bond.This type of situation may lead to cooperative phenomena between magnetism and proton dynamics in the future. In this paper, we describe the crystal structures and the magnetic properties of three acid–base molecular compounds: p-PYNN2 HQ, p-PYNN2 FA and p-PYNN2 SA diox. We analyzed their crystal structures, focusing on selectivity and the features of the hydrogen bonds.The observed selectivity in the hydrogen bonds was interpreted in terms of competition between the electrostatic and the charge-transfer terms in the hydrogen bonding energy. In addition, the likelihood of molecular recognition in the hydrogen-bonding formation was analyzed. J O U R N A L O F C H E M I S T R Y Experimental p-PYNN was prepared according to the procedure previously described.9 HQ, FA and SA were of reagent grade and were used as commercially obtained.The molecular compounds, p- PYNN2 HQ and p-PYNN2 FA were prepared as follows: p- PYNN and HQ (or FA) in 251 proportion were dissolved in acetone at 40 °C, and their crystals were grown with slow evaporation of the solvent at 0 °C.The molecular compound of p-PYNN and SA was obtained following the same procedure using water–dioxane (251) instead of acetone. Crystallization took place with dioxane to give p-PYNN2 SA diox. Selected IR data n:/cm-1 (KBr): 3232 (m, br; OH st.), 1596 (m; pyridyl J. Mater. Chem., 1998, 8(5), 1157–1163 1157 Materialsring st.) for PYNN (m; pyridyl ring st.) for p-PYNN2 FA; 2574 (m, br; NH st.), 1630 (m; pyridyl ring st.) for p-PYNN 2 HQ; 2440 and 1933 (m, br; OH st.), 1603 2 SA diox.X-Ray diVraction data were collected on a Rigaku AFC-5S 2 FA) automatic four-circle diVractometer 2 HQ and p-PYNN2 SA diox, or using 26 reflections (p-PYNN2 HQ and p-PYNN2 SA diox) or a Mac Science MXC18 ( p-PYNN with graphite-monochromatized Mo-Ka radiation (l= 0.71073 A°). Unit cell dimensions were obtained by a leastsquares refinement, using 25 reflections with 20°<2h<25° for p-PYNN with 30°<2h<35° for p-PYNN2 FA.During data collection, the intensities of three representative reflections were measured as a check on crystal stability, and no loss was observed. No absorption correction was performed, because the influence of the absorption was negligible.The crystal structures were solved by direct methods (SHELXS-8610 and DIRDIF11). Block-matrix-diagonalization least-squares refinement (UNICS-III12) with anisotropic thermal parameters for all non-hydrogen atoms was employed for p-PYNN2 SA diox bond. The intermolecular distance between O(1) O(18) is bridged the NO groups of separate p-PYNNs with a hydrogen and p-PYNN2 HQ.The positions of the hydrogen atoms were 2.728(5) A °. This type of hydrogen bond has been observed in found by diVerential Fourier methods and they were refined the complex of phenylboronic acid and phenyl nitronylnitroxisotropically with a fixed thermal parameter in order to avoid ide: viz. the acid bridge in the NO groups of the nitronylnitroxan excessive number of parameters.A refinement for the nonide in the solid state.15 hydrogen atoms in p-PYNN2 FA was performed by using the Table 3 shows the atomic charges on the skeleton of pfull-matrix least-squares method with anisotropic thermal par- PYNN calculated using the geometry in the bulk crystal.16 ameters.The positions of the hydrogen atoms were calculated, Table 3 also shows the calculated spin densities. As a common and were refined with isotropic thermal parameters at a characteristic of the nitronylnitroxide radical family, the posigeometrically restrained position. Details in regards to the tive spin densities are concentrated on the NO groups since crystallographic parameters are given in Table 1.Full crystallothe oxygen atom in the NO group has the largest negative graphic details excluding structure factors have been deposited charge. The spin polarization slightly penetrates the aromatic at the Cambridge Crystallographic Data Centre (CCDC). See substituent at the a carbon (the pyridyl ring) and alternation Information for Authors, J.Mater. Chem., 1998, Issue 1. Any of the positive and negative spin densities is observed on request to the CCDC for this material should quote the full the skeleton. literature citation and the reference number 1145/85. Static magnetic susceptibilities and magnetization were measured in a 1 T field on a Faraday balance, which has been previously described.13 The temperature dependence of the magnetic susceptibility was examined at 3–280 K.Molecular orbital calculations were performed with the MOPAC package,14 in order to estimate the atomic charges and the spin densities on p-PYNN. PYNN2 HQ C30H36O6N6 578.67 monoclinic P21/n P21/n P19 26.24(1) 6.806(2) 8.330(3) 94.61(3) 1480.0(9)2 2 1 1.299 1.310 1.329 Mo-Ka (l=0.71073 A °, graphite monochromator) 3658 1542 0.0677 0.0602 Crystal structures 1/n space group.The structure of the p- expected to result in an antiferromagentic coupling. Since the stacking columns are separated from each other by the HQ Table 1 Crystal data and experimental conditions for p-PYNN2 HQ, p-PYNN2 FA and p-PYNN2 SA diox p-PYNN2 HQ The 251 complex of p-PYNN and HQ crystallizes in the monoclinic P2 PYNN2 HQ unit is shown in Fig. 1, in which half of the unit compound formula formula weight crystal system space group a/A ° b/A ° c/A ° a(°) J. Mater. Chem., 1998, 8(5), 1157–1163 b(°) c(°) V /A °3 Dc/g cm-3 radiation Z2h range (°) 55 measured observed W RR1158 Fig. 1 Molecular structures in the p-PYNN2 HQ unit is crystallographically independent. The selected bond distances and angles are listed in Table 2. The HQ molecule Fig. 2(a) and (b) show projections of the crystal structure of p-PYNN2 HQ parallel and perpendicular to the b axis, respectively. In Fig. 2(b) the HQ molecules are omitted for the sake of clarity. There is a one-dimensional stacking column of p-PYNN along the b axis, in which the molecules are arranged head-to-tail.In the intermolecular arrangement, the short intermolecular distances are 3.370(7) for O(1) C(16)i and 3.347(6) A °for N(5) C(6)i [symmetry operation; (i) 0.5-x, y+0.5, 0.5-z]. The former indicates a spatial overlap between the positive spin densities on the neighboring molecules and the latter between the negative spin densities.According to McConnell’s spin polarization mechanism,17 these kinds of overlaps between polarized spin densities of the same sign are PYNN2 SA diox PYNN2 FA C32H42O10N6 670.72 C28H36O8N6 584.63 triclinic monoclinic 14.970(5) 7.552(2) 13.090(5) 8.988(2) 13.011(4) 7.894(3) 93.69(3) 92.58(3) 102.58(3) 109.82(2) 837.9(5) 1478.5(8) 554176 3555 0.0531 0.0541 604809 2250 0.0691 0.0823Table 2 Selected bond lengths (A °) and angles (°) for p-PYNN2 HQ bond length/A ° 1.277(6) 1.343(5) 1.390(7) 1.385(7) 1.385(6) O(2)MN(4) C(6)MC(13) C(15)MN(5) C(13)MC(17) C(19)MC(21) O(1)MN(3) N(4)MC(6) C(14)MC(15) C(16)MC(17) C(19)MC(20) O(1)MN(3)MC(6) N(3)MC(6)MN(4) C(13)MC(14)MC(15) C(15)MN(5)MC(16) C(16)MC(17)MC(13) O(18)MC(19)MC(21) bond angle (°) 126.4(4) 107.8(4) 118.0(4) 115.7(4) 118.8(4) 123.4(4) 119.2(4) C(19)MC(20)MC(21)i (i ) Symmetry operation; x:-1, y:, z:-1.Table 3 Atomic charge and spin density distribution on p-PYNN as obtained by the PM3-UHF method H(9a)~(9c) O(1) H H H C(9) H(14) H(15) C(14) C(15) H(10a)~(10c) N(3) C(7) H H C(10) H C(6) C(13) N(5) N(4) C(17) C(16) H C(11) C(8) H H(11a)~(11c) H H(17) C(12) H H H H(16) spin densities 0.33102 0.43052 -0.18245 -0.50487 0.02126 0.00950 0.01297 0.26929 -0.25617 0.20464 -0.00069 -0.00079 0.01451 -0.01229 O(2) atomic charges -0.53200 0.68960 -0.04680 -0.43240 -0.14115 -0.06480 -0.08155 0.03010 -0.10165 -0.06480 0.04785 0.05150 0.12180 0.10065 H(12a)~(12c) atom(s) O(1), O(2) N(3), N(4) N(5) C(6) C(7), C(8) C(9), C(11) C(10), C(12) C(13) C(14), C(17) C(15), C(16) H(9a)~(9c), H(11a)~(11c) H(10a)~(10c), H(12a)~(12c) H(14), H(17) H(15), H(16) molecules, the magnetic interaction between the columns would be very weak.p-PYNN2 FA P2 The structure of p-PYNN2 FA belongs to the monoclinic 1/n space group. The geometry of p-PYNN2 FA is shown in Fig. 3. Selected bond distances and angles are listed in Table 4. The organic acid FA occupies the space between the pyridyl rings of p-PYNNs.There is an intermolecular hydrogen bond between the OH group of FA and the nitrogen atom [i.e. N(5)] on the pyridyl ring of p-PYNN, although N(5) is less electronegative than O(1) and O(2) in the NO groups (see Table 3). The charge-transfer term would contribute to the hydrogen bond contact here, as will be discussed later. The intermolecular, interatomic distance between N(5) O(18) is 2.634(2) A °, indicating the presence of a strong hydrogen bond.The asymmetric bond distances in the CO2 moiety of FA [1.317(4) A °for C(21)–O(18) and 1.208(4) A °for C(21)–O(19)] indicate that the hydrogen on the intermolecular N O distance remains on the side of FA (i.e. OMH N). This is further supported by the fact that the IR spectrum shows two broad n(OH) stretching bands at 2440 and 1933 cm-1.Usually, 1.350(6) 1.392(6) 1.321(6) 1.284(5) 1.456(6) 1.327(7) N(3)MC(6) C(13)MC(14) N(5)MC(16) 1.383(5) O(18)MC(19) 1.401(6) 1.377(6) 125.5(4) 117.2(4) 125.5(5) O(2)MN(4)MC(6) C(14)MC(13)MC(17) N(5)MC(15)MC(14) N(5)MC(16)MC(17) O(18)MC(19)MC(20) C(20)MC(19)MC(21) 124.8(4) 116.9(4) 119.7(4) 121.0(4) C(19)MC(21)MC(20)i (i) 0.5-x, y+0.5, 0.5-z] Fig. 2 Projection of the crystal structure of p-PYNN2 HQ (a) parallel to the b axis and (b) perpendicular to the b axis [symmetry operation: Fig. 3 Molecular structures in the p-PYNN2 FA unit 1159 J. Mater. Chem., 1998, 8(5), 1157–1163Table 4 Selected bond lengths (A °) and angles (°) for p-PYNN2 FA bond length/A ° 1.279(4) 1.353(3) 1.388(4) 1.386(4) 1.208(4) O(2)MN(4) C(6)MC(13) C(15)MN(5) C(13)MC(17) C(20)MC(21) O(1)MN(3) N(4)MC(6) C(14)MC(15) C(16)MC(17) O(19)MC(20) bond angle (°) 126.2(2) 108.3(2) 118.3(3) 117.5(3) 118.6(3) 112.6(2) 122.3(3) O(1)MN(3)MC(6) N(3)MC(6)MN(4) C(13)MC(14)MC(15) C(15)MN(5)MC(16) C(16)MC(17)MC(13) O(18)MC(20)MC(21) C(20)MC(21)MC(21)i (i ) Symmetry operation; 1-x, 1-y, 1-z .Fig. 4 Projection of the crystal structure of p-PYNN2 FA onto the ab plane [symmetry operation: (i) x, y-1, z] these bands are observed in a strongly asymmetric, doubleminimum hydrogen bond in complexes of carboxylic acids and pyridines.18 Fig. 4 shows a projection of the crystal structure on to the ab plane.The p-PYNN molecules show side-by-side and headto-head stacking along the b axis. The short distances in the stacking are 3.192(3) A °for O(1) C(16)i and 3.347(3) A °for O(1) C(17)i [symmetry operation; (i) x, y-1, z]. There are hydrogen bonds between O(1) in the NO group and the hydrogen atoms, H(16)i and H(17)i, on the pyridyl ring.The contact O(1) H(16)i is an overlap between the positive and negative spin densities, while the contact O(1) H(17)i is one between the positive spin densities. The magnetic interactions appear to be competing in this arrangement. The two-dimensional sheet shown in Fig. 4 is stacked along the c axis with a screw relationship. There was no significant contact in the intersheet arrangement. p-PYNN2 SA diox The adduct crystallizes in the triclinic P19 space group. Fig. 5 shows the structure of the p-PYNN2 SA diox unit. Selected sites: (a) the oxygen in the NO group and (b) the nitrogen on J. Mater. Chem., 1998, 8(5), 1157–1163 1160 1.351(3) 1.397(3) 1.334(4) 1.274(4) 1.465(3) 1.334(4) 1.317(4) 1.307(4) 1.398(3) 1.491(4) N(3)MC(6) C(13)MC(14) N(5)MC(16) O(18)MC(20) C(21)MC(21)i 126.1(3) 118.2(2) 123.8(3) 123.5(3) 124.2(3) 123.2(3) O(2)MN(4)MC(6) C(14)MC(13)MC(17) N(5)MC(15)MC(14) N(5)MC(16)MC(17) O(18)MC(20)MO(19) O(19)MC(20)MC(21) Fig. 5 Molecular structures in the p-PYNN2 SA diox unit [symmetry operation: (i ) x:, 1-y, 1-z] Fig. 6 shows the structure of p-PYNN bond distances and angles are listed in Table 5.The SA molecule bridges the gap between the pyridyl rings of the p- PYNNs, as well as FA in p-PYNN2 FA. The intermolecular, interatomic distance N(5) O(18) is 2.578(2) A °, which is shorter than that in p-PYNN2 FA. It is significant that the two oxygen atoms of the SA molecule which are attached to two separate p-PYNN molecules are diagonal to each other, and not adjacent to each other.In addition, the SA molecule is on a crystallographic inversion symmetry centre and has little bond alternation: the bond distances C(20)MO(18) and C(21)MO(19) are 1.241(3) and 1.211(2) A °, respectively, and C(20)MC(21) and C(20)MC(21)i are 1.433(3) and 1.492(3) A °, respectively [symmetry operation; (i) x:, 1-y, 1-z].The structure and coordination of SA indicate that the molecule is a squarate dianion in which the two protons are missing and the proton in the N O intermolecular contact is attached to p-PYNN (i.e. O- H+-N-). 2 SA diox. In the crystal, p-PYNN acts as a dimer with a short distance between the NO groups: the distances O(1) O(1)ii and O(1) N(3)ii are 3.667(2) and 3.658(2) A °, respectively [symmetry operation; (ii ) x:-1, y:, z-1].Since the positive spin densities are concentrated on the NO groups, there would be a large overlap between them, thereby resulting in antiferromagnetic coupling in the dimer. The arrangement resembles that of p-N-methylpyridinium nitronylnitroxide (abbreviated as p-MPYNN) in its iodide salt.19 p-MPYNN has a substituent (methyl group) at the pyridyl nitrogen atom and a positive charge on the pyridinium ring, as well as the N-protonated p-PYNN in p- PYNN2 SA diox.The arrangement of p-MPYNN in p- MPYNN I resulted in a strong antiferromagnetic coupling.19 Selectivity in hydrogen bonds of p-PYNN The crystal structures of the 251 molecular complexes of p- PYNN and three organic acids with diVerent acidity have been examined.The three acids formed diVerent hydrogen bonds with p-PYNN, which involved two hydrogen-bond acceptingTable 5 Selected bond lengths (A °) and angles (°) for p-PYNN2 SA dioxa bond length/A ° 1.274(2) 1.354(3) 1.371(3) 1.370(3) 1.211(2) 1.426(3) O(2)MN(4) C(6)MC(13) C(15)MN(5) C(13)MC(17) C(20)MC(21) O(22)MC(24) O(1)MN(3) N(4)MC(6) C(14)MC(15) C(16)MC(17) O(19)MC(21) O(22)MC(23) O(1)MN(3)MC(6) N(3)MC(6)MN(4) C(13)MC(14)MC(15) C(15)MN(5)MC(16) C(16)MC(17)MC(13) O(18)MC(20)M(21)i bond angle (°) 127.1(2) 108.4(2) 119.5(2) 120.7(2) 119.5(2) 134.5(2) 135.3(2) 135.3(2) 110.4(2) O(19)MC(21)MC(20) C(20)MC(21)MC(20)i O(22)MC(23)MC(24)iii a(i ) Symmetry operation; x:-1, 1-y, 1-z: (iii) Symmetry operation; 1-x, 1-y, z.ON+ ON+ NON+ Fig. 6 View of the crystal structure of p-PYNN2 SA diox [symmetry operation: (ii ) x:-1, y:, z:-1] the pyridyl ring. The features of the hydrogen bonds in the three are shown in Scheme 1. The acidic hydrogen of HQ attached to site (a) (OMH O), while FA and SA selected site (b).In addition, the hydrogen bond in p-PYNN p-PYNN2 SA diox is ionic (O- H+MN). The distance between the two atoms connected by the hydrogen bond becomes longer in the order p-PYNN2 HQ, p-PYNN2 FA, p-PYNN2 SA diox. The nature of the hydrogen bond [AMH B] can be expressed on the whole by the following five configurations:20 4 A- H+MB 5 A H-MB+ 2 A-MH+ B 1 AMH B 3 A+MH- B Structures 1, 2 and 3 produce the electrostatic stabilization energy EEL of the hydrogen bond, while structures 4 and 5 cause the charge transfer stabilization ECT.Since HQ is a very weak acid, electrostatic stabilization terms 1, 2 and 3 play a dominant role in the hydrogen bonds of HQ, and the contributions of 4 and 5 which are given by the dissociation of the AMH bond must be small.Therefore, the more electronegative oxygen in the NO group of p-PYNN would be chosen as the hydrogen-bond acceptor in the crystal of p-PYNN2HQ. On the other hand, FA and SA are much stronger acids than HQ, and the ECT in their hydrogen bonds which is produced by 2 FA is neutral (OMH N), while that in configurations 4 and 5 must be larger than that in the hydrogen bond of HQ.Here, the binding energies of the HMB bonds in the CT states govern the hydrogen bonds. With regard to the of the H+MN bond at site (b) would be larger than that of two hydrogen-bond acceptors in p-PYNN, the binding energy the HMON bond at (a). Therefore strong acids are considered to prefer site (b) to (a) as a hydrogen bond acceptor.This is why site (b) was chosen in the crystals of p-PYNN2 FA and p-PYNN2 SA diox. The hydrogen bond in p-PYNN2 FA is neutral and the acidic hydrogen remains in FA. This indicates that EEL is still eVective in p-PYNN2 FA, in addition to ECT . The hydrogen bond in p-PYNN2 SA diox is ionic, indicating the superiority of ECT over EEL .The pKa diVerence between the pyridinium ions and the carboxylic acids in aqueous solution, which is denoted as DpKa , was used to analyze the hydrogen bonds in various pyridine–carboxylic acid complexes in solution or even in the solid state.18 The hydrogen bond would be ionic when DpKa>3.75, and would be neutral when it is less than that value.The selectivity and features of the hydrogen bonds in the three molecular compounds of p-PYNN Scheme 1 J. Mater. Chem., 1998, 8(5), 1157–1163 1.353(2) 1.385(3) 1.335(3) 1.275(3) 1.459(3) 1.333(3) 1.241(3) 1.492(3) 1.503(3) 1.400(3) 1.433(3) 1.417(3) N(3)MC(6) C(13)MC(14) N(5)MC(16) O(18)MC(20) C(20)MC(21)i C(23)MC(24)iii 126.2(2) 118.1(2) 121.3(2) 120.9(2) 134.1(2) 91.4(2) O(2)MN(4)MC(6) C(14)MC(13)MC(17) N(5)MC(15)MC(14) N(5)MC(16)MC(17) O(18)MC(20)MC(21) C(21)MC(20)MC(21)i 136.1(2) 109.6(2) 111.0(2) O(19)MC(21)MC(20)i C(23)MO(22)MC(24) O(22)MC(24)MC(23)iii N N HO OH •O O• N N N HO O O O N N OH N+ OONH+ O O N O 2- O N O O +HN N+ ON+ O- 1161EL can be qualitatively explained in terms of the competition between E and ECT in the hydrogen bonds, which depends on the acidity of the organic acids and on the binding energy of hydrogen to the two hydrogen bond accepting sites in p-PYNN.(1) 0+a1x+a2x2 1+a3x+a4x2+a5x3 2 FA. The between the protonated p-PYNNs in p-PYNN2 SA diox is As mentioned previously, the intermolecular arrangement similar to that of p-MPYNN in p-MPYNN I.The meta derivative (m-MPYNN) exhibits a strong ferromagnetic intermolecular interaction on an unusual lattice named Kagome.23 Research on protonated m-PYNN is now in progress. Magnetic properties The temperature dependences of the magnetic susceptibilities of the three compounds were examined in the temperature range 3–280 K.The correction for the diamagnetic contribution was performed by using the diamagnetic susceptibilities that were evaluated assuming that the paramagnetic component follows the Curie law at high temperatures. The paramagnetic susceptibilities, xp , obtained are shown in Fig. 7, where the molar unit is defined as half of the p-PYNN2 X unit and a logarithmic scale was used in order to clarify the lowtemperature behavior.The open circles in Fig. 7 show the temperature dependence p p of x for p-PYNN2 HQ. The value of xp increases with a decrease in temperature to 5 K and, after reaching a maximum, it decreases with a further decrease in temperature. Below 5 K, x approaches a non-zero value at absolute zero.The behavior can be interpreted in terms of an antiferromagnetic onedimensional chain,21 using eqn. (1); x= 4C a Twith x=|J |/2kBT , B constants a0–a5 have been defined elsewhere,22 |J | is the ferromagnetic spin-coupler in the molecular compound of searchers found that phenylboronic acid acts as a magnitude of intrachain magnetic coupling, C the Curie con- (phenylboronic acid) (phenyl nitronylnitroxide) through an stant and k the Boltzmann constant.The solid curve in Fig. 7 NO HOMBMOH ON pathway.15 However, there is no which goes through the plots for p-PYNN2 HQ is the best suggestion of a magnetic interaction through the hydrogen theoretical fit for eqn. (1) with parameters |J |/kB=4.7 K and bonds in the three compounds, even though HQ bridges the C=0.376 emu mol-1 (fixed).As described in the previous NO groups in p-PYNN HQ. This could be responsible for section, the p-PYNN radicals form a one-dimensional stacking the fact that the distances between the acidic hydrogen atoms column along the b axis in p-PYNN2 HQ (see Fig. 2). The are much longer in the three acids than in the boronic acid.stack should be assigned to the antiferromagnetic chain. The squares in Fig. 7 show the results of p-PYNN value of xp gradually increases with a decrease in temperature in the temperature range studied. This behavior can be interpreted in terms of the Curie–Weiss law. The solid curve which Fig. 7 Temperature dependences of the paramagnetic susceptibilities xp in a log scale for (#) p-PYNN2 HQ, (%) p-PYNN2 FA and ($) p-PYNN2 SA diox. The solid curves are theoretical ones (see the text).J. Mater. Chem., 1998, 8(5), 1157–1163 1162 was fitted to the plots for p-PYNN2 FA is the best theoretical fit of the Curie–Weiss law with a Curie constant of C=0.376 emu (fixed) and a Weiss constant of h=-0.68 K.The weak magnetic interaction would be caused by the cancellation between the ferromagnetic and antiferromagentic contributions in the arrangement shown in Fig. 4. The closed circles in Fig. 7 show xp for p-PYNN2 SA diox. The value of xp increases with a decrease in temperature from 280 to 22 K; below that it shows a decrease. The increase of xp below 4 K would be caused by Curie spins on the lattice defects. Since p-PYNN exists as a dimer in the crystal of p- PYNN2 SA diox, the temperature dependence of xp can be interpreted, as follows, based on the singlet–triplet model, eqn.(2); Cdef (2) x= 4C exp(2J/kBT ) T 1+3 exp(2J/kBT ) + T where J is the intradimer antiferromagnetic coupling constant and Cdef is the Curie constant for the lattice defect.The solid curve that was fitted to the plots for p-PYNN2 SA diox in Fig. 7 is the best theoretical fit of eqn. (2) whose parameters are J/kB=-18.5 K, C=0.376 emu K mol-1 (fixed) and Cdef= 0.015 emu K mol-1. The theoretical curve can explain the observed behavior. The three molecular compounds exhibited diVerent magnetic properties. This reflects the diVerence in the molecular arrangements of p-PYNN in these compounds. Their intermolecular magnetic interactions can be understood in terms of the McConnell’s spin polarization mechanism. Other re- 2 Conclusion We analyzed the crystal structures and the magnetic properties of the three acid–base molecular complexes, p-PYNN2 HQ, p-PYNN2 FA and p-PYNN2S diox. The organic acids formed selective hydrogen bonds to the two kinds of hydrogenbond accepting sites in p-PYNN. The acidic hydrogen of HQ attached to the oxygen (OMO), while FA and SA selected the nitrogen on the pyridyl ring of p-PYNN. The hydrogen bond in p-PYNN2 FA was neutral (OMHN), while that in p-PYNN2 SA diox was ionic (O-H+MN). The hydrogen bonding patterns that we observed in the three crystals were qualitatively interpreted, in terms of the competition between the electrostatic stabilization and the charge-transfer stabilization in the hydrogen bond. This depends on the acidity of the organic acids and on the proton accepting abilities of the two sites in p-PYNN. The possibility of selective, controllable hydrogen-bond production is suggested. The three molecular compounds exhibit diVerent antiferromagnetic properties, which are dependent on the intermolecular arrangement of p-PYNN in the crystals. Their magnetic couplings are explained, based on the McConnell’s spin polarization mechanism. This work was supported by a Grant-in-aid for ScientificResearch from the Ministry of Education, Science, and Culture, of the Japanese government. References

ISSN:0959-9428    

DOI:10.1039/a708121i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Two spin-containing fragments connected by a two-electron one-center heteroatom p spacer. A new open-shell organic molecule with a singlet ground state Ll. Viadel,a J. Carilla,a E. Brillas,b A. Labartac and L. Julia�*a aDepartament de Quý�mica Orga`nica Biolo`gica, Centre d’Investigacio� i Desenvolupament (CISC), Jordi Girona 18–26, 08034 Barcelona, Spain bDepartament de Quý�mica Fý�sica, Universitat de Barcelona, Avgda. Diagonal 647, 08028 Barcelona, Spain cDepartament de Fý�sica Fonamental, Universitat de Barcelona, Avgda.Diagonal 647, 08028 Barcelona, Spain The synthesis of 4,4-iminobis(2,2¾,2,4¾,4,6,6¾,6-octachlorotriphenylmethyl) diradical 3, a stable organic magnetic molecule consisting of two spin-containing fragments linked by a nitrogen atom, is reported.Electron paramagnetic resonance (EPR) analysis in methyltetrahydrofuran solution (~10-3 M) at low temperatures showed a typical fine structure (gxx=2.0042; gyy=2.0048; gzz=2.0027) of Dms=±1 transition (|D/hc|=0.0071 cm-1; |E/hc|=0.0006 cm-1) as well as a broad (DHpp=7.5 G) and weak signal of Dms=±2 transition (g=4.124), due to an asymmetric and excited triplet state corresponding to an intramolecular spin–spin interaction which diminishes with decreasing temperature.It also showed a pair of small peaks, that might be associated with a weaker dipole–dipole interaction which diminishes with increasing temperature, emerging at both sides of a central and single peak due to a doublet state resonance corresponding to 2,2¾,2,4¾,4,6,6¾,6-octachloro-4-{3,5-dichloro-4- [bis(2,4,6-trichlorophenyl)methylene]cyclohexa-2,5-dienylideneamino}triphenylmethyl radical 4, obtained by smooth oxidation of 3.From magnetic susceptibility measurements of the sample in the solid, a linear four-spin model was applied to establish that the singlet is the ground state of the molecule and that two triplets (Jintra=-286±30 K, J¾inter=-160±50 K) were the low-lying excited states.Organic solutions of 3 in air slowly oxidize to give 4, a much more persistent monoradical which is also obtained by a smooth oxidation of 3 with AgNO3 in CHCl3. Cyclic voltammograms for the reduction of 3 and 4 in dimethylformamide (DMF) with tetra-n-butylammonium perchlorate exhibited three consecutive redox couples with standard potentials of -0.23,-0.58 and -0.74 V vs.SCE, indicating a reasonable stability of anions 3 - and 32- in DMF solution. There is great current interest in the preparation of organic molecular materials with new magnetic properties.1 Organic molecules with paramagnetic behavior are those with openshell electronic structures where one or more electrons are unpaired.These molecules are called radicals or polyradicals, and they are normally transient and very reactive to air, moisture and, in general, to their environment. Thus, if free radicals are to be good candidates for magnetic materials, it has to be possible to prepare, handle and store them without diYculty. The stability of the carbon-centered radicals is mainly achieved by steric protection.2,3 In highly chlorinated triphenylmethyl radicals, this protection is mainly accomplished by the six aromatic chlorines in the ortho-positions surrounding the trivalent carbon atom.3 Thus, this kind of very stable free radical is completely unassociated in crystalline solids with no appreciable decomposition either in solid or in solution. The synthesis of new polyradical molecules of great persistence and their physical properties involving magnetic behavior have recently been published.4,5 The preparation of radical amino 1,6 a new polychlorotriphenylmethyl radical of the TTM [tris (2,4,6-trichlorophenyl)- C• Cl Cl Cl Cl Cl Cl Cl Cl Cl TTM C• NH2 Cl Cl Cl Cl Cl Cl Cl Cl 1 C+ Cl Cl Cl Cl Cl Cl Cl Cl Cl 2 SbCl6 – methyl] series, as a potential radical intermediate in the synthesis of many new polyradicals which use the characteras a diradical of the TTM series, the amino-diradical 3, whose istics and extensive reactivity of the amino group, has also two spin-bearing moieties, the triphenylmethyl radicals, are recently been published. The isolation of a secondary reaction held together by the amine function, bonded in the para- product which could be identified, from preliminary analysis position of a phenyl of each moiety.The radical 3 is easily results, as a secondary amine, resulting from the condensation oxidized in solution to a new and very persistent paramagnet, of two molecules of the hydrocarbon salt 25a with ammonia the imino-radical 4. followed by reduction with SnCl2, was also mentioned.6 It is now possible to fully describe this new secondary amine Lahti et al.have carried out semi-empirical calculations to J. Mater. Chem., 1998, 8(5), 1165–1172 1165predict the ground state spin multiplicity of a large number of Cyclic voltammetry (CV) systems composed of two doublets, organic oxyl radicals, or A cyclic voltammogram for the reduction of a solution of two triplets, methylenes or organic nitrenes, connected by a 0.5 mM amino-diradical 3 in dimethylformamide (DMF) with spacer consisting of a magnetic coupling unit.7 When the 0.1 M tetra-n-butylammonium perchlorate (TBAP) is presented spacer is a heteroatom,7b oxygen or nitrogen, they predicted in Fig. 1. In the potential range between 0 and -1.2 V three an antiferromagnetic coupling in the para,para¾ connectivity, consecutive redox couples, O1/R1, O2/R2 and O3/R3, with that was stronger with a nitrogen atom as spacer than with respective standard potentials E0 of-0.23,-0.58 and-0.74 V an oxygen atom.In non-planar geometries, this interaction vs. SCE (NaCl-saturated calomel electrode) can be observed. dropped substantially to give nearly degenerate high-spin and No more peaks were found for 3 at potentials higher than low-spin in the ground-state. -1.2 V.The above redox couples were also recorded in the In Lahti’s terminology, the magnetic material 3 consists of cyclic voltammograms of a saturated solution of the iminotwo spin-containing (SC) fragments, two carbon-centered radradical 4 in DMF (Fig. 2), along with a further irreversible icals, connected by a two-electron one-center heteroatom peak R4.The diVerent height of the peaks in Fig. 1 and 2 is p spacer, a nitrogen atom. Due to the relative stability of 3, due to the lower concentration of 4 than 3, whereas the described below, its properties could be tested and the predicpresence of the additional peak R4 in Fig. 2 can be ascribed tions regarding the multiplicity of its electronic ground-state to reaction of 4 with electrogenerated radicals at the electrode corroborated.reaction layer. Fig. 1 also shows that O2/R2 and O3/R3 couples partially overlapped, and for this reason the height of peaks Results R2, R3 and O2 cannot be accurately determined. In fact, the O1R1, O2/R2 and O3/R3 couples behaved as reversible one- The reaction of the hydrocarbon salt 25a with an excess of electron systems controlled by diVusion.So the diVerences ammonia in CH2Cl2 followed by treatment with SnCl2 gave between the anodic and cathodic peak potentials (Epa-Epc) the amino-radical 16 (58%), the diradical 3 (17%) and a low for each of these three couples was close to 60 mV in all scan yield of the TTM radical8 (9%) as a direct reduction of salt 2 rates (n) considered, whereas the height of peaks R1, R2+R3, (Scheme 1).The amino-diradical 3 is a green microcrystalline solid with a visible spectrum in cyclohexane as follows: l/nm (e/dm3 mol-1 cm-1), 375 (40 600), 440 (15 200), 633 (17 700). It is stable in the solid state (its decomposition in 13 d in air is practically nil, checked by electronic spectroscopy), and it oxidizes in solution to the more persistent imino-radical 4.A smooth oxidative treatment of 3 with a basic aqueous solution of silver nitrate in chloroform gave 4 quantitatively, which, by the action of SnCl2 in tetrahydrofuran, reverted to 3. Radical 4 is an extremely persistent dark brown solid, even in solution ark. Its visible spectrum in cyclohexane is as follows; l/nm (e/dm3 mol-1 cm-1), 377 (37 350), 409 (29 400), 573 (15 100), 619 (12 700).Fig. 1 Cyclic voltammogram of a 0.5 mM amino-radical 3 solution in 0.1 M TBAP+DMF. Scan rate 50 mV s-1 and temperature 25 °C. Starting and final potential 0 V; reverse potential -1.2 V. Fig. 2 Cyclic voltammogram of a saturated imino-radical 4 solution in 0.1 M TBAP+DMF under the same experimental conditions as NH Cl Cl (C6H2Cl3)2C• + 1 + TTM 2 3 2 (1) NH3, CH2Cl2 (2) SnCl2, THF Cl Cl C6H2Cl3 = Cl C • Cl Cl Cl Cl NH Cl 2 2 3 AgNO3, NaOH, HCl3 SnCl2, THF C Cl Cl Cl Cl Cl C Cl Cl Cl Cl N Cl • 2 2 4 Scheme 1 indicated in Fig. 1 1166 J. Mater. Chem., 1998, 8(5), 1165–1172O1 and O2+O3 increased linearly with the square root of the from coplanarity, due to the presence of the six ortho-chlorines in the phenyl rings. The stability of 32- is then mainly scan rate.9 Note that the height of peaks R2+R3 was approxiattributed to steric protection.mately equal to that of peaks O2+O3 and twice that of peak As shown in Fig. 2, a saturated solution of 4 in DMF with R1. However, the |Ipa|/Ipc ratio (Ipa=anodic peak current, TBAP (0.1 M) displayed the same O1/R1, O2/R2 and O3/R3 Ipc=cathodic peak current) for the O1/R1 pair was ca. 0.6 pairs as 3. In this case, the height of peaks R2+R3 is only 1.4 (Fig. 1). times that of peak R1. In addition, the |Ipa|/Ipc ratio for the The CV behavior for 3 described above helps to establish corresponding O1/R1 couple was ca. 1 in all n tested, as that the O1/R1 couple corresponds to the equilibrium reaction expected if all amino-diradical 3 formed in peak R1 is also between the imino-radical 4 and the amino-diradical 3, i.e.oxidized to imino-radical 4 in peak O1. The height of peaks eqn. (1), R1 and O1 for compound 4 in a given n value was similar to 4+H++1 e-P3 (1) that of peak O1 found for compound 3. Since these peaks are diVusion-controlled, their heights must be proportional to the where H+ proceeds from a proton donor such as water, always solubility of 4, i.e.its concentration in the saturated solution. present in small amounts in DMF. The O2/R2 pair can then This suggests that the |Ipa|/Ipc ratio of ca. 0.6 found for the be ascribed to the reversible conversion of 3 into its radical- O1/R1 couple of compound 3 (Fig. 1) is due to the loss of anion 3 -: eqn.(2), compound 4 near the electrode towards the bulk solution 3+1 e-P3·- (2) during the oxidation of 3 in peak O1 until reaching its saturation in the reaction layer. So, by comparing the height and the O3/R3 couple to the equilibrium (3) between 3 - and of the diVusion-controlled peak R1 for compounds 3 and 4, its dianion 32-. which must be directly proportional to their concentrations, 3 -+1 e-P32- (3) the solubility of 4 in DMF was found to be 0.31 mM.The presence of peak R4 in Fig. 2 is more diYcult to explain. The presence of three consecutive reversible one-electron redox This irreversible peak has a height similar to that of peak R1, pairs for compound 3 (Scheme 2) indicates a good stability of which means it is diVusion-controlled.In addition, the diVeranions 3 - and 32- in DMF, without the existence of any chemience between its cathodic half-peak and peak potentials, cal reaction involving their disappearance from the medium. (Ep/2c-Epc), was 70–80 mV, whereas its Epc value varies lin- In addition, the small diVerence between the second and early with -log n with a slope close to 30 mV per decade. All third cathodic peaks (160 mV) in 3 is a measure of the small these parameters agree with the behavior expected for a firstinteractions between the two negative charges in the dianion order one-electron EC mechanism [theoretical values at 32-, which must be situated apart from each other to prevent 25.0 °C:9 (Ep/2c-Epc)=59.6 mV, slope of Epc vs.-log n plot= Coulombic repulsions between them.By analogy with the 29.6 mV per decade]. electronic structure in the neutral radical, in 32- the charges The fact that the height of peaks R2+R3 in Fig. 2 is will be located mainly in the aliphatic carbon atoms of each significantly lower than twice that of peak R1, indicates that triphenylmethyl moiety adopting a stable conformation far not all of the compound 3 formed in this last peak is completely converted into 3 - and 32-, i.e.part of these ions disappears at the reaction layer. This phenomenon is not observed in cyclic voltammograms of 3 (Fig. 1) and suggests a reaction of 3 - and 32- with 4, present in the reaction layer by its diVusion from bulk solution, yielding the electroactive species of peak R4. A reversible one-electron reduction of this species, followed by an irreversible chemical decomposition of the resulting compound, could explain the EC process found for this peak.Electron paramagnetic resonance (EPR) Recently, the X-band EPR spectrum of the amino-radical 1 recorded in CH2Cl2 solution at 173 K was reported.6 It displayed an overlapping triplet of septets, centered at g= 2.0030, corresponding to the hyperfine splitting of the free electron with the nitrogen atom (aN=1.10 G) and the six aromatic meta-hydrogens (aH=1.10 G).The magnetic interaction with the a-amino hydrogen ones gave negligible splitting and most probably contributes to line broadening. The spectrum found for the isotropic solution (~10-3 M) of amino-diradical 3 in 2-methyltetrahydrofuran (MTHF) at room temperature contained a single broad line centered at g=2.0036 with a peak-to-peak linewidth of the derivative line, DHpp=6.2 G.This large linewidth value and the existence of abnormally intense tails in the derivative line, which increase with decreasing temperature, are accounted for by the modulation of the energies of the triplet spin levels due to the anisotropic part of the intramolecular electron–electron magnetic interaction.These large absorptions probably hamper the observation of satellite lines corresponding to the coupling with 13C nuclear spins of carbons in the molecule, mainly those from a-carbons where the majority of the spin density resides,10 and preclude any information in fluid solution about the strong or weak electron–electron exchange coupling (the scalar part of the magnetic interaction between two unpaired electrons) which will be expressed by a normal or a half value C Cl Cl Cl Cl Cl C Cl Cl Cl Cl N Cl • 2 2 4 C Cl Cl Cl Cl Cl C Cl Cl Cl Cl NH Cl • 2 2 3 • C Cl Cl Cl Cl Cl C Cl Cl Cl Cl NH Cl • 2 2 3–• C Cl Cl Cl Cl Cl C Cl Cl Cl Cl NH Cl 2 2 32– – – – +1e– +1e– +1e– +1H+ Scheme 2 of those coupling constants, respectively.11 J.Mater. Chem., 1998, 8(5), 1165–1172 1167At low temperatures (~150 K), in a very viscous solution near to glassy MTHF, the spectrum showed three pairs of lines in the Dms=±1 region (Fig. 3), typical of a randomly oriented ensemble of immobilized triplet species without axial symmetry, described by the zero-field splitting parameters |D/hc|=0.0071 cm-1 and |E/hc|=0.0006 cm-1, with the principal values of the g tensor being gxx=2.0032, gyy=2.0037 and gzz=2.0029.Further confirmation of the triplet state configuration was provided by the observation of the Dms=±2 region of a broad line centered at g=4.124, with a peak-to-peak spacing, DHpp=7.5 G (Fig. 3). Although the fine structure in the Dms=±1 remains at lower temperatures in the rigid glass MTHF, the intensity rapidly decreases with decreasing temperature, being hardly detected at temperatures lower than 70 K, which is consistent with the fact that the triplet is an excited state.In addition, an intense central line corresponding to S=1/2 species (g=2.0032) appears, which can be ascribed to the imino-radical 4 always present in the sample as an impurity, resulting from the smooth oxidation of aminodiradical 3.From parameter D, the average distance between the two unpaired electrons has been estimated12 as 7.15 A° , a smaller value than the theoretical one of 9.1 A ° .13 At lower temperatures and in conditions of microwave saturation of the doublet state resonance (power: 5.02 mW), a pair of signals (g=2.0034) emerging from the edges of the central line in the region Dms=±1 appears.In Fig. 4, the Fig. 5 (a) A series of EPR spectra of a solution of 3 in MTHF glass spectrum recorded at 90 K shows the presence of both inter- from 4 to 90 K (microwave power, 0.2 mW), showing the intensity dependence of the weak dipole–dipole interaction as explained in the actions, the strong one with a fine structure of three pairs of text, and (b) the EPR spectrum at 4 K lines of low intensity and the weak one with a closer pair of lines emerging from the wings of the strong single line.In Fig. 5, a series of spectra recorded from 4 to 90 K, irradiating ance. At much lower microwave power (10-3 mW), the intenthe sample at low microwave power (0.2 mW) in conditions sity of the central line gradually decreases from 4 K upwards, of non-saturation of these lateral signals is displayed.In this following Curie’s law in the temperature range 37–90 K, where series, while the intensity of the lateral signals diminishes from the signal amplitude is inversely proportional to the tempera- 4 K upwards, in such a way that they practically disappear at ture (Fig. 6). So, both signals, the doublet and the central 59 K, the intensity of the central signal increases from 4 to single line, must correspond to diVerent species, as shown by 90 K, due to microwave saturation of the doublet state resonselective microwave saturation, and the idea that the doublet might correspond to a weak ferromagnetic interaction in the ground state between pairs of molecules, since its intensity increases with decreasing temperature is not discarded.The EPR spectrum of imino-radical 4 in tetrachloroethylene solution at room temperature consisted of a single line, DHpp= 2.6 G, centered at g=2.0037 [Fig. 7(a)]. At higher gain, the isotropic coupling with the 13C nuclear spins of the a-carbon atoms in the molecule appeared in the spectrum with a coupling constant, a#15 G.This value is practically half the value corresponding to the 13C hyperfine coupling in radicals of the TTM series5a,c,6 (a#29.5 G), which indicates that the spin density on these carbons is also half the normal value and, consequently, the electronic structure of 4 can be depicted Fig. 3 EPR spectrum of 3; Dms=±1 transition in MTHF glass at 150 K. Insert shows the signal corresponding to Dms=±2 forbidden transition Fig. 6 A series of EPR spectra of a solution of 3 in MTHF glass from Fig. 4 EPR spectrum of 3; Dms=±1 transition in MTHF glass at 90 K, showing the presence of the two dipole–dipole interactions, as 4 to 90 K (microwave power, 10-3 mW), showing the normal intensity dependence of the doublet state resonance, as explained in the text explained in the text 1168 J.Mater. Chem., 1998, 8(5), 1165–1172Fig. 8 Thermal variation of meff/mB for amino-diradical 3 ($) from sample measured in a Faraday balance operating with a field-strength of 17 kOe and (#) from sample measured in a SQUID magnetometer operating with a field-strength of 20 kOe. The solid lines are theoretical ones, as described in the text. As shown in Fig. 8, when the temperature decreases from 300 K, the meff value of both microcrystalline samples decreases continuously. This behavior is associated with a strong antiferromagnetic interaction. In the range 12–75 K, there is a plateau of meff=0.73 and meff=1.04 mB for the two samples, respectively, which suggests that some monoradical impurities exist in greater proportions in one of the samples.After applying diVerent models to account for these results, the model which best fits the experimental data is of a system composed of a couple of diradical molecules with an intramolecular interaction characterized by J, interacting with each other at a strength given by J¾ (Fig. 9).14 In such a system, Fig. 7 EPR spectrum of 4 (a) in tetrachloroethylene at room temperature and (b) in CH2Cl2 at 213 K there is a proportion of monoradical impurities, most probably the oxidized imino-radical 4, which diVers from one sample to the next.as a structure in resonance between the two canonical structures shown in Scheme 3. A hyperfine splitting of an overlapping multiplet of lines appeared in the spectrum when recorded in CH2Cl2 at low temperatures (213 K and lower) [Fig. 7(b)]. Magnetic susceptiblity Fig. 9 Model system for diradical interaction The molar magnetic susceptibility (xS) of diradical 3 was The spin Hamiltonian for such a system is given by eqn. (4), measured in two diVerent samples in the temperature range 4–300 K, one of them with a SQUID magnetometer and the H=-2JS1S2-2J¾S2S3-2JS3S4 (4) other one with a Faraday balance operating in a field-strength where Si corresponds to the spin angular momentum vector of 20 and 17 kOe, respectively.The data (x¾S =xS-xdia- for the single electron in each center. xholder) were corrected for the magnetization of the sample The total spin states and energies, li, corresponding to this holder and for the diamagnetic susceptibility of the molecule system are obtained from the diagonalization of the (-608.7×10-6 cm3 mol-1, using Pascal’s constants).The ther- Hamiltonian [eqn. (5)] mal variation of the molar eVective magnetic moment in Bohr magnetons shown in Fig. 8 is given by meff=2.828(x¾ST )1/2. Quintuplet (S=2) l1=-J- J¾ 2 Triplet (S=1) l2=J- J¾ 2 Triplet (S=1) l3= J¾ 2 +EJ¾2+J2 Triplet (S=1) l4= J¾ 2 -EJ¾2+J2 Singlet (S=0) l5= J¾ 2 +J+2SAJ¾ 2 B2 - J¾ 2 J+J2 Singlet (S=0) l6= J¾ 2 +J-2SAJ¾ 2 B2 - J¾ 2 J+J2 (5) C Cl Cl Cl Cl Cl C Cl Cl Cl Cl N Cl • 2 2 C Cl Cl Cl Cl Cl C Cl Cl Cl Cl N Cl 2 2 • Scheme 3 The expression for the susceptibility, using the van Vleck J.Mater. Chem., 1998, 8(5), 1165–1172 1169states of the molecule into a ground state singlet and an excited triplet. On the other hand, weaker interactions either in the glassy solution or in the solid state are also predicted by EPR and susceptibility measurements, respectively.At present, we are not able to attribute the first one which increases with decreasing temperature, but the second one is ascribed to an intermolecular antiferromagnetic interaction. Fig. 10 Diagram of levels for the singlet ground state and two triplet Concerning the intramolecular interaction, Lahti et al.preexcited states dicted, by using AM1-CI semi-empirical procedures, a strongly antiferromagnetic coupling in the para,para¾ connectivity in this kind of system in their planar conformation, with a formula,15 is as in eqn. (6), dominant closed-shell configuration in their ground state, best described by a pair of equivalent zwitterionic Kekule� resonance xd= xD 2 = Nm2Bg2 6kBT structures.All these predictions are confirmed in amino-diradical 3. Results from EPR analysis and susceptibility measurements, × 30 e-b1+6 e-b2+6 e-b3+6 e-b4 5 e-b1+3 e-b2+3 e-b3+3 e-b4+e-b5+e-b6 (6) as shown above, established the singlet character of the ground state of 3, which is best described as a resonance of the where: bi=li/kBT , N is the Avogadro number, mB is the Bohr canonical structures shown in Scheme 4.magnetron, g is the Lande� factor, kB is the Boltzmann constant, However, the remarkable persistence of polychlorotriphenylxD is the susceptibility of a cluster compound of two diradical methyl radicals is mainly attributed to steric shielding by the molecules and xd is the susceptibility per molecule.six chlorines surrounding the trivalent carbon, which leads to The expression for the susceptibility of the monoradical a torsion of the phenyl rings around their bond with the impurity is eqn. (7). central carbon. As a result, these radicals adopt a stable propeller-like conformation with a significant inhibition of the xM= Nm2B g2 4kBT (7) delocalization of the free electron into the three rings.In the stable non-planar conformation most of the spin density is in Then, the thermal dependence of meff for the whole system the central carbon. becomes as in eqn. (8hese findings suggest that in amino-diradical 3, the diradical structure plays an important role in the configuration of meff/mB=2.828 its ground state if the twisted geometry is the most stable conformation, with the free electron mainly confined to the ×S TFm T-hm 3 8 +(1-Fm) T T-hd central carbon atom of each triphenylmethyl moiety.In such a case, the dipolar spin–spin interaction is much weaker than × 15 eb1+3 e-b2+3 e-b3+3 e-b4 10 e-b1+6 e-b2+6 e-b3+6 e-b4+2 e-b5+2 e-b6 (8) in the planar conformation, as also predicted by Lahti et al.,7b and the triplet–singlet energy gap is not very high, 1.38 kcal mol-1 (1 cal=4.184 J) as stated above.assuming g=2, where: Fm is the fraction of monoradical impurity and (1-Fm)=Fd is the fraction of diradical molecules On the other hand, the fact that the average distance between the unpaired electrons is smaller than the theoretical one, as and hm and hd account for the eVect of residual path interactions among molecules which are not considered in the model.described in the EPR section, favours the closed-shell electronic structures, where the molecule is forced to adopt a more planar This equation was fitted to the experimental data obtained for both samples to give the following parameters: (a) from conformation between the two a-carbons. These conformations make the delocalization of the electronic spin on the phenylene sample analyzed in the SQUID: Fm=0.19±0.02; Fd= 0.81±0.02; hm=-1.50±0.5 K; hd=-1±1 K; J= rings easier than on the four extreme phenyls.Concerning the intermolecular interaction in the solid state, -290±20 K; J¾=-203±40 K; (b) from sample analyzed in the Faraday balance: Fm=0.37±0.02; Fd=0.63±0.02; hm= it is obvious that the proposed model of a weak interacting dimer from magnetic susceptibility measurements can only -1.1±0.8 K; hd=-1±1 K; J=-296±30 K; J¾= -160±50 K.The values of J and J¾ are quite similar for both provide a simplified picture of the real situation, but it does involve enough radical centers and interactions among them samples although they display diVerent impurity content.The diagram of levels for the singlet ground state, l6, and to reproduce the low lying energy terms with suYcient accuracy. If the detailed treatment of the interactions with other the first two triplet excited states of the system, the lowest triplet l4 and the next l2 considering the above values for J radical centers (e.g. the tendency to form a linear chain) is and J¾ and their intervals of error, can be established as shown in Fig. 10. The highest excited states, one singlet, one triplet and one quintuplet, the three of energy too high to be significantly populated in the normal range of temperatures, are not considered. The low negative values for hm and hd indicate the existence of small residual antiferromagnetic interactions among molecules. Discussion Amino-diradical 3 is a clear and stable example of a system composed of two spin-bearing units linked by a two-electron one-center heteroatom p spacer.Both the EPR analysis and the results from magnetic susceptibility measurements predict a strong dipole–dipole interaction, either in dilute solution (EPR) or in the solid (susceptibility), which is attributed to the C Cl Cl R R C H N Cl Cl R R + C Cl Cl R R C H N Cl Cl R R + C Cl Cl R R C H N Cl Cl R R – • • – Scheme 4 intramolecular electron spin–spin interaction, splitting the spin 1170 J.Mater. Chem., 1998, 8(5), 1165–1172included in the model, neither the spin multiplicity of the three 4-Amino-2,2=,2==,4=,4==,6,6=,6==-octachlorotriphenylmethyl radical 1 and 4,4-iminobis(2,2=,2==,4=,4==,6,6=,6==- low-lying levels varies nor the energy values change significantly.octachlorotriphenylmethyl ) diradical 3 So, it can be concluded that a ground singlet state with a Dry NH3 was passed slowly in the dark, through a solution total pairing of the spins and, at least, two triplets as the of salt 2 (2.12 g) in CH2Cl2 (500 ml) until the blue color of nearest excited states, is the low-lying energy diagram which the solution suddenly changed to red.Then argon was passed achieves a good fit of the experimental data for amino-diradical through to eliminate the NH3 and the resulting mixture was 3 in the solid state. filtered. The filtrate was evaporated to dryness and the red residue was dissolved in THF (100 ml). Anhydrous SnCl2 (0.56 g) was added to the solution, and the mixture was stirred in the dark at room temperature for 30 min.The resulting Experimental mixture was filtered and evaporated to dryness. The residue General procedures in diethyl ether (100 ml), washed with aqueous NaHCO3 and with water, then dried and evaporated, gave a new residue All melting points are uncorrected. Solvents were dried and which was chromatographed (silica gel flash chromatography, purified before use.THF was freshly distilled from sodium CCl4–CHCl3, 151) to give the following: (a) radical 1 (0.26 g; benzophenone ketyl. Magnetic susceptibility data for microcry- 9%) identified by mp and IR. (b) Amino-diradical 3 (0.14 g; stalline samples of amino-diradical 3 were measured from 4 to 17%), mp 268–271 °C; n/cm-1 (KBr) 3400 (w), 3100 (w), 1565 298 K with a Manics DSM8 susceptometer operating with a (s), 1525 (m), 1370 (m), 1310 (m), 1180 (m), 1130 (m), 1075 (w), field strength of 17 kOe and with a SQUID magnetometer 1055 (w), 980 (w), 920 (w), 850 (m), 820 (m), 805 (m), 790 (m); operating with a field strength of 20 kOe.UV–VIS (cyclohexane) lmax/nm (e/dm3 mol-1 cm-1) 375 (40 600), 440 (15 200), 633 (13 700).Anal. Calc. for C38H13Cl16N: 43.4; H, 1.25; N, 1.3; Cl, 54.0. Found: C, 43.9; Electrochemical measurements H, 1.4; N, 1.3; Cl, 53.9%. (c) Radical TTM (0.74 g; 58%), identified by its mp and IR. The cyclic voltammetric experiments were carried out in a three-electrode cell under an argon atmosphere. A platinum Oxidation of 3. Synthesis of 2,2=,2==,4=,4==,6,6=,6==-octachloro-4- sphere with a surface area of 0.093 cm2 was used as the working {3,5-dichloro-4-[bis(2,4,6-trichlorophenyl )methylene]cyclo- electrode and a Pt wire as the counter electrode.The reference hexa-2,5-dienylidenamino}triphenylmethyl radical 4 electrode was an SCE (NaCl-saturated aqueous solution) connected to the cell through a salt bridge containing a 0.1 M To a solution of 3 (20 mg) in CHCl3 (5 ml) at room temperature TBAP–DMF solution.The temperature of test solutions and was added a basic aqueous solution of AgNO3 (5 ml, AgNO3 of the SCE was kept at 25 °C. In all experiments, the cell 2%, NaOH 2%) and the resulting mixture was vigorously was maintained in darkness to avoid the photochemical stirred for 5 min in the dark. The organic solution was washed decomposition of substrates in solution.with water, dried and evaporated to dryness, giving a residue CV measurements were performed with standard equipment which was chromatographed (silica gel, CHCl3) to give 4 consisting of a PAR 175 universal programmer, an Amel 551 (18 mg; 90%), mp>350 °C; n/cm-1 (KBr) 3080 (w), 1550 (s), potentiostat and a Philips 8043 X-Y recorder. Cyclic voltam- 1530 (s), 1370 (s), 1285 (w), 1180 (m), 1130 (s), 1075 (w), 960 mograms of all solutions were recorded at a scan rate (n) of (w), 920 (w), 885 (w), 850 (s), 820 (m), 800 (s), 785 (s); UV–VIS 20–200 mV s-1.(cyclohexane) lmax/nm (e/dm2 mol-1 cm-1) 210 (128 000), 376 A solution of amino-diradical 3 (0.5 mM) in DMF containing (37 000), 413 (31 000), 573 (15 000), 621 (12 000).Anal. Calc. TBAP (0.1 M) as the background electrolyte was studied. Since for C38H12Cl16N: C, 43.5; H, 1.1; N, 1.3; Cl, 54.0. Found: C, imino-radical 4 showed lower solubility in DMF, its CV 43.0; H, 1.1; N, 1.3; Cl, 54.3%. measurements were carried out using a saturated solution in DMF with TBAP (0.1 M). The volume of all test solutions Reduction of 4 to give 3 was 25 ml.Anhydrous SnCl2 (5 mg) was added to a solution of 4 (20 mg) in CHCl3 (5 ml) and the mixture was vigorously stirred at room temperature and in the dark (30 min). Then, the solvent EPR experiments was evaporated oV and the residue in CHCl3 was filtered (silica EPR spectra were recorded with a Varian E-109 spectrometer gel ) to give 3 (19 mg; 97%), identified by IR and UV–VIS working in the X band and using a Varian E-257 temperature- spectra.controller to obtain spectra at temperatures as low as 130 K. A Bruker ESP 300 spectrometer with a Bruker ER 4112 HV Support of this research by DGICYT of MEC (Spain) through continuous-flow liquid helium cryostat and an Oxford project PB92-0031 is acknowledged. The authors express their Instruments temperature-controller system was used to obtain gratitude to the EPR services of the Centre d’Investigacio� i EPR spectra at lower temperatures (4 K).Samples of amino- Desenvolupament (CSIC) and the Universitat de Barcelona. diradical 3 and imino-radical 4 were prepared in quartz EPR tubes and degassed by three freeze–pump–thaw cycles before References being inserted into the EPR cavity. Handling of radicals in solution was performed in the dark. 1 For reviews see: J. S. Miller, A. J. Epstein and W. M. ReiV, Chem. Rev., 1988, 88, 201; Acc. Chem. Res., 1988, 21, 114; H. Iwamura, Adv. Phys. Org. Chem., 1990, 26, 179; D. A. Dougherty, Acc. Chem. Res., 1991, 24, 88; H. Iwamura and N. Koga, Acc. Chem. Res., 1993, Tris(2,4,6-trichlorophenyl )carbenium hexachloroantimonate 2 26, 346; H.Kurreck, Angew. Chem., Int. Ed. Engl., 1993, 32, 1409; J. S. Miller and A. J. Epstein, Angew. Chem., Int. Ed. Engl., 1994, SbCl5 (1.5 ml) was slowly added to a solution of tris(2,4,6- 33, 385; A. Rajca, Chem. Rev., 1994, 94, 871. trichlorophenyl)methyl radical8 (1.80 g) in CCl4 (240 ml), and 2 D. Griller and K. U. Ingold, Acc. Chem. Res., 1976, 9, 13. the mixture was left at room temperature under an argon 3 M.Ballester, Acc. Chem. Res., 1985, 18, 380 and references cited atmosphere for 24 h. The precipitate was filtered, washed with therein; M. Ballester, Adv. Phys. Org. Chem., 1989, 25, 267 and CCl4 and dried, and identified as salt 2 (2.78 g; 96%), dark references cited therein. 4 J. Veciana, C. Rovira, O. Armet, V. M. Domingo, M. I. Crespo and blue crystals mp 183–185 °C ( lit.5a mp 180–182 °C).J. Mater. Chem., 1998, 8(5), 1165–1172 1171F. Palacio, Mol. Cryst. L iq. Cryst., 1989, 176, 77; J. Veciana, T. Kaneko, Y. Kuzumaki, E. Tsuchida and H. Nishida, J. Org. Chem., 1994, 59, 4272. C. Rovira, M. I. Crespo, O. Armet, V. M. Domingo and F. Palacio, J. Am. Chem. Soc., 1991, 113, 2552; J. Carilla, L. Julia�, J. Riera, 8 O. Armet, J. Veciana, C.Rovira, J. Riera, J. Castan� er, E. Molins, J. Rius, C. Miravitlles, S. Olivella and J. Brichfeus, J. Phys. Chem., E. Brillas, J. A. Garrido, A. Labarta and R. Alcala� , J. Am. Chem. Soc., 1991, 113, 8281; J. Veciana, C. Rovira, N. Ventosa, 1989, 91, 5608. 9 Z. Galus, Fundamentals of Electrochemical Analysis, Harwood, M. I. Crespo and F. Palacio, J. Am. Chem. Soc., 1993, 115, 57; V. M. Domingo, J. Castan� er, J. Riera and A. Labarta, J. Org. Chichester, 1976, ch. 7, p. 9; H. Lund and M. M. Baizer, Organic Electrochemistry. An Introduction and a Guide, Marcel Dekker, Chem., 1994, 59, 2604; R. Chaler, J. Carilla, E. Brillas, A. Labarta, New York, ch. 2, p. 3. Ll. Fajarý�, J. Riera and L. Julia�, J. Org. Chem., 1994, 59, 4107; 10 H. R. Falle, G. R. Lukhurst, A. Horsefield and M. Ballester, M. Ballester, I. Pascual, C. Carreras and J. Vidal-Gancedo, J. Am. J. Chem. Phys., 1969, 50, 258. Chem. Soc., 1994, 116, 4205. 11 D. C. Reitz and S. I.Weissman, J. Chem. Phys., 1960, 33, 700. 5 (a) J. Carilla, Ll. Fajarý�, L. Julia� , J. Riera and Ll. Viadel, 12 The distance between the two a-carbons has been calculated from T etrahedron L ett., 1994, 35, 6529; (b) S. Lo� pez, J. Carilla, Ll. Fajarý�, standard angles and bond lengths, and assuming that the CMN L. Julia� , E. Brillas and A. Labarta, T etrahedron, 1995, 51, 7301; bond length is 1.426 A ° and the CMNMC angle is 108.0°. (c) J. Carilla, Ll. Fajarý�, L. Julia� , J. San� e� and J. Rius, T etrahedron, 13 A. M. Trozzolo, R. W. Murray and E. Wasserman, J. Am. Chem. 1996, 52, 7013. Soc., 1962, 84, 4990. 6 L. Teruel, Ll. Viadel, J. Carilla, Ll. Fajarý�, E. Brillas, J. San�e� , J. Rius 14 T. Mitsumori, K. Inoue, N. Koga and H. Iwamura, J. Am. Chem. and L. Julia�, J. Org. Chem., 1996, 61, 6063. Soc., 1995, 117, 2467. 7 (a) P. M. Lahti, A. S. Ichimura and J. A. Berson, J. Org. Chem., 15 R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, 1989, 54 958; (b) J. Org. Chem., 1991, 56, 3030; (c) C. Ling, Heidelberg, 1986, p. 21. M. Minato, P. M. Lahti and H. van Willigen, J. Am. Chem. Soc., 1992, 114, 9959; (d) M. Minato, P. M. Lahti and H. van Willigen, J. Am. Chem. Soc., 1993, 115, 4523; (e) N. Yoshioka, P. M. Lahti, Paper 7/07993A; Received 6th November, 1997 1172 J. M

ISSN:0959-9428    

DOI:10.1039/a707993a

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials New 1,3-dithiol-2-ylidene donor–p–acceptor chromophores with intramolecular charge-transfer properties, and related donor–p–donor molecules: synthesis, electrochemistry, X-ray crystal structures, non-linear optical properties and theoretical calculations Adrian J. Moore,a Martin R. Bryce,*,a Andrei S. Batsanov,a Andrew Green,a Judith A. K. Howard,a M.Anthony McKervey,b Peter McGuigan,b Isabelle Ledoux,c Enrique Ortý�,d Rafael Viruela,d Pedro M. Viruelad and Brian Tarbite,† aDepartment of Chemistry, University of Durham, Durham, UK DH1 3L E bSchool of Chemistry, T he Queen’s University, Belfast, N. Ireland, UK BT 9 5AG cCNET-France T e� le�com, 196, Avenue Henri Ravera BP 107, 92225 Bagneux, France dDepartamento de Quý�mica Fý�sica, Universidad de Valencia, E-46100 Burjassot, Valencia, Spain eGreat L akes Chemical (Europe) L td, AycliVe Industrial Estate, Newton AycliVe, Co.Durham, UK DL 5 5HA New donor–p–acceptor chromophores 5a–c, 7a–c, 8a–c, 13a–c and 14b–c have been synthesised: substituted 1,3-dithiole derivatives span a range of donor abilities [viz. 4,5-dimethyl.4,5-bis(methylsulfanyl).4,5-bis(methoxycarbonyl)], a conjugated ethylenic or oligoethylenic linker varies the central p-electron unit (one, two and four conjugated double bonds) and dicyanomethylene and N-cyanoimine groups are the acceptor units.Extended tetrathiafulvalene derivatives 15a–c have also been synthesised. The electronic absorption spectra of compounds 5, 7, 8 and 14 reveal a broad low-energy intramolecular chargetransfer band [lmax(MeCN) 354–533 nm] which shifts bathochromically with increasing donor strength of the dithiole ring, and with increasing length of the conjugative pathway.The solution redox properties of 5, 7, 8 and 14, studied by cyclic voltammetry, reveal a reversible one-electron oxidation wave, attributed to the formation of the radical cation of the 1,3-dithiol-2-ylidene moiety, and an irreversible one-electron reduction to form the radical anion located on the dicyanomethylene or N-cyanoimine groups.For the bis(dithiole) donors 15a–c a single two-electron redox wave is observed. The non-linear optical (NLO) properties of 7a–c and 14b have been determined using the EFISH technique: moderate NLO properties are observed for compounds 7a–c [m.b(0) 85–112×10-48 esu] whereas for the more extensively conjugated compound 14b, the value is increased to m.b(0) 1170×10-48 esu.The molecular structure and electronic properties of the unsubstituted (R=H) compounds 7, 8, 14 and 15 have been calculated within the density functional theory approach. The minimum energy conformation corresponds to the trans orientation of the side chain for 7, and the cis orientation for 8, in agreement with X-ray crystal structures and solution NMR data.The redox properties and electronic spectra are discussed on the basis of molecular orbital energies and topologies. The X-ray crystal structures of compounds 7b, 8b and 15b are reported. In 7b the 1,3-dithiol-2-ylidene and dicyanopropene systems are planar and form an angle of 3° between each other; the ‘butadiene’ unit has a trans configuration.Molecule 8b is planar (with the exception of the methyl groups) and the imine nitrogen atom is in a syn orientation towards the dithiole group, forming a short intramolecular S · · · N contact [2.719(6) A ° ]. For both 7b and 8b p-delocalisation is observed within the central conjugated spacer unit.Molecule 15b has a predominantly planar structure, with the central tetraene unit in an all-trans configuration. Asymmetric conjugated molecules containing electron donor the field of organic molecular metals, as it is a constituent part of the well known p-donor tetrathiafulvalene (TTF) 1, and the and electron acceptor substituents (D–p–A) have been thoroughly explored in the design of materials having highly synthesis and electrochemistry of 1,3-dithiole derivatives is well developed and understood.2 The use of the 1,3-dithiol-2-ylidene eYcient second-order non-linear optical (NLO) chromophores. 1 A prototypical example is 4-nitroaniline. Molecular group as an electron donor has been reported previously by Gompper et al.,3 and by Katz et al.4 in their investigations of non-linearity (bm) of such compounds is dependent on the eVective length of p-conjugation and the strength of the donor benzenoid type non-linear optical chromophores.Lehn and co-workers5 have also employed the 1,3-benzodithiol-2-ylidene and acceptor substituents. Whilst a wide variety of acceptor groups have been examined for their role in influencing the group in their studies on push–pull carotenoids.Jen et al.6 have discussed the role of a number of 1,3-dithiol-2-ylidene molecular NLO properties, relatively few electron donor moieties have continued to receive the most attention (e.g. dialkyl- derivatives in thiophene derived chromophores. Baudy-Floc’h and co-workers7 have studied the NLO properties of some 2- amino and alkoxy groups).In the search for other electron donating groups we focus in this paper on derivatives of the imino-4-amino-1,3-dithioles and Wegner and co-workers8 have 1,3-dithiole heterocycle. This ring system has, to date, received limited attention as a donor component in D–p–A materials. This is surprising since it has been the centre of studies within *E-mail m.r.bryce@durham.ac.uk †Present address: Seal Sands Chemicals Ltd., Seal Sands Road, Seal Sands, Middlesbrough, UK TS2 1UB.S S S S S S CN CN 1 2 J. Mater. Chem., 1998, 8(5), 1173–1184 1173incorporated a substituted benzo-1,3-dithiol-2-ylidenedicyano- the reaction of aldehydes 6a–c with N,N-bis(trimethylsilyl)- carbodiimide and titanium tetrachloride (according to the methylene unit into the backbone of a main-chain polymer.During the preparation of this manuscript, other groups have conditions developed by Aumu� ller and Hu� nig19) in dichloromethane at room temperature resulted in the formation of the reported new 1,3-dithiole–p–A systems.9 To date, very little attention has been given to the potentially corresponding N-cyanoimine derivatives 8a–c (78–85%). Malealdehyde 9, which can be prepared in a high state of important interplay that functionality on the 1,3-dithiole ring may have in modulating the degree of intramolecular charge- purity by the oxidation of furan with distilled dimethyldioxirane (DMD) in acetone,20 has been eYciently intercepted transfer in D–p–A materials.With this in mind, we have synthesised a range of novel D–p–A structures, varying the D, in Wittig reactions.21 In particular, in situ reaction with one equivalent of triphenylphosphoranylideneacetaldehyde p and A fragments: substituted 1,3-dithiol-2-ylidene derivatives span a range of donor abilities [viz. 4,5-dimethyl.4,5- aVorded, after work-up and isomerisation (induced either thermally or by treatment with iodine), (E,E)-mucondialdehyde bis(methylsulfanyl).4,5-bis(methoxycarbonyl)], a conjugated ethylenic or oligoethylenic linker varies the central p-electron 1022 (62%) (Scheme 3).Compounds 14b and 14c were conveniently prepared in a two-step procedure from compound unit (one, two and four conjugated double bonds) and the dicyanomethylene and N-cyanoimine groups have provided 10. Compound 10 was first condensed with ylides 12a–c (generated in situ from phosphonium salts 11a,17 11b18 and the acceptor functionality.10 11c23 in tetrahydrofuran by addition of triethylamine) to aVord compounds 13a–c (54–79% yields). Compounds 13a and 13b Results and Discussion were the only isolated products, even when an excess of ylides 12a and 12b was used in this reaction, whereas the extended Synthesis of 5a–c, 7a–c, 8a–c, 13a–c and 14b–c bis(1,3-dithiole) donor 15c (14%) was isolated along with The first, and one of the simplest, D–p–A compounds utilising compound 13c (54%) whent of ylide 12c was a 1,3-dithiol-2-ylidene donor, compound 2,11 was prepared by employed (see below).Subsequent reaction of compounds 13b Mayer et al. during early pioneering investigations of the and 13c with Lehnert’s reagent (as described above) aVorded chemistry of the 1,3-dithiolium cation.12 Using a similar procompounds 14b and 14c (43 and 87% yield, respectively).cedure, we have now synthesised derivatives 5a–c (Scheme 1). Surprisingly, compound 14a could not be obtained by this Thus, methylation of 1,3-dithiole-2-thiones 3a,13 3b14 and 3c15 procedure. Attempts at reacting compounds 13a–c with N,Nwith methyl trifluoromethanesulfonate aVorded 1,3-dithiolium bis(trimethylsilyl )carbodiimide and titanium tetrachloride in cations 4a–c (93–97%), which on reaction with malononitrile dichloromethane (as above for compounds 6a–c) gave only using pyridine as base gave, after spontaneous elimination of unchanged starting aldehydes.methanethiol, compounds 5a–c (61–67% yields).We next targeted compounds 7a–c with an additional double bond in Synthesis of bis(1,3-dithiol-2-ylidene)hexa-2,4-diene derivatives the spacer unit. These were readily prepared in 64–71% yields 15a–c by reaction of Lehnert’s reagent (malononitrile, titanium tetrachloride and pyridine)16 with the known aldehydes 6a,17 6b18 The incorporation of conjugated linking groups between the 1,3-dithiole rings of TTF has been widely explored and 6c17 in refluxing dichloromethane (Scheme 2).Similarly, as a structural modification of the p-donor unit. In parti- S S SMe R R S S CN CN R R S S S R R (ii) 4a 4b 4c 5a 5b 5c CF3SO3 R = Me R = MeS R = CO2Me R = Me R = MeS R = CO2Me 3a 3b 3c (i) R = Me R = MeS R = CO2Me Scheme 1 Reagents and conditions: (i ) CF3SO3Me, CH2Cl2, 20°C, 2 h; (ii) H2C(CN)2, pyridine, PriOH, 20 °C, 3 h S S O R R S R R CN S CN O O O O O HA HB HC HD HE HA HB HC HD HE HF HF S S R R PR'3 H S S R R PR'3 (iv) 14b 14c (i) 13a 13b 13c R = Me R = MeS R = CO2Me R = MeS R = CO2Me (ii), (iii) 9 10 BF4 – 11a 11b 11c R = Me, R' = Bu R = MeS, R' = Ph R = CO2Me, R' = Bu 12a 12b 12c R = Me, R' = Bu R = MeS, R' = Ph R = CO2Me, R' = Bu (v) Scheme 3 Reagents and conditions: (i) DMD, acetone, 0 °C, 0.5 h; S S R R S S R R S S R R CN CN O N CN HA HB HA HB (ii) (i) 8a 8b 8c 6a 6b 6c 7a 7b 7c R = Me R = MeS R = CO2Me R = Me R = MeS R = CO2Me R = Me R = MeS R = CO2Me Scheme 2 Reagents and conditions: (i) CH2(CN)2, TiCl4, pyridine, (ii) Ph3PCHCHO, CH2Cl2, 0�20 °C, 3 h; (iii) I2, CH2 Cl2, 20°C, 0.5 h; (iv) 10, NEt3, THF, 20 °C, 24 h; (v) CH2(CN)2, TiCl4, pyridine, CH2Cl2, reflux, 24 h; (ii) Me3SiNCNSiMe3, TiCl4, pyridine, CH2Cl2, 20 °C, 48 h CH2Cl2, reflux, 24 h 1174 J. Mater.Chem., 1998, 8(5), 1173–1184S S R R PBu3 H S S S S R R R R BF4 15a 15b 15c (i) 11a R = Me 11c R = CO2Me 11d R = MeS R = Me R = MeS R = CO2Me Scheme 4 Reagents and conditions: (i ) (a) For compound 15a: LDA, S S O R R 16a R = Me 16b R = CO2Me 16c R-R = (CH=CH)2 16d R-R = SCH2CH2S 13a, THF, -78�20 °C, 16 h; (b) for compounds 15b and 15c: 10, NEt3, THF, 20 °C, 24 h for an (ABC)2 spin system were simulated using LAOCOON software and good agreement with the experimental data was cular, olefinic,24 quinonoid25 and heterocyclic26 spacers have found.32 Definitive confirmation of the all trans stereochemistry attracted considerable attention and extensively conjugated of compound 15b was provided by X-ray analysis (see below).derivatives are of interest in the context of organic molecular wires.27 The rationale behind the design of TTF derivatives X-Ray molecular structures of compounds 7b, 8b and 15b with extended conjugation is that the oxidised states respon- The single crystal structures of compounds 7b, 8b and 15b sible for conduction in charge-transfer complexes and radical have been determined by X-ray diVraction (Table 1).In mol- cation salts should be stabilised by decreased intramolecular ecule 7b (Fig. 1) the dithiol-2-ylidene and dicyanopropene Coulombic repulsion. As a continuation of our interest in systems are planar and form an angle of 3° between each extended p-donors24d,f,j,25a and having a ready supply of other.The torsion angles around the C(2)–S(3) and C(3)–S(4) dialdehyde 10, we were attracted to the target compounds bonds are 7 and 86°, respectively. Thus all the non-hydrogen 15a–c. As noted above, reaction of equimolar amounts of the atoms, except C(10), are approximately coplanar and all the ylide derived from phosphonium salt 11c and dialdehyde 10 multiple bonds and sulfur atoms [except S(4)] can participate aVorded both the desired aldehyde 13c and the bis(1,3-dithiole) in p-conjugation. The ‘butadiene’ moiety has a trans-configur- derivative 15c (54 and 14% yields, respectively).Reaction of ation; the formally single C(4)–C(5) bond is only 0.016 A ° (4s) 2.5 equivalents of phosphorane 12c with 10 increased the yield longer than the formally double bonds.Thus, the system is of 15c (66%, aldehyde 13c was also isolated in 14% yield). much closer to a cyanine (bond-equivalent) structure, than to Similar reactions of dialdehyde 10 with up to 4 equivalents of genuine all-trans polyenes with the mean alternation (D) phosphoranes 12a and 12b gave only aldehydes 13a and 13b between single and double bond lengths of 0.10–0.12 A ° .33 Such as the isolated products (45 and 70% yields, respectively).Using the more reactive ylide derived from tributylphosphon- Table 1 Crystal data ium salt 11d28 (2.5 equivalents) in this reaction gave extended donor derivative 15b in 68% yield (along with aldehyde 13b, compound 7b 8b 15b 18%).The tetramethyl analogue 15a was obtained (40%) by formula C10H8N2S4 C8H8N2S4 C16H18S8 the deprotonation of Wittig reagent 11a in THF at -78 °C M 284.42 260.40 466.78 symmetry triclinic orthorhombic monoclinic using LDA as base, following the known literature proa/ A ° 5.062(1) 15.791(1) 9.808(2) cedure,17,24a in the presence of aldehyde 13a (Scheme 4). b/A ° 9.144(3) 8.140(1) 7.575(2) c/A ° 14.051(5) 8.878(1) 14.090(3) 1H NMR Spectra of compounds 7, 8, 14 and 15 a (°) 85.75(3) 90 90 b (°) 83.24(3) 90 93.92(2) Previous structural studies on 1,3-dithiole derivatives,29 1,2- c (°) 87.92(2) 90 90 dithiole derivatives30 and trithiapentalene analogues31 bearing U/A ° 3 643.8(3) 1141.2(2) 1044.4(4) substituents capable of strong intramolecular S · · ·X (X=O, S) T/K 150 150 150 interactions have shown they exist in a favoured s-cis confor- radiation Mo-Ka Mo-Ka Cu-Ka l/A ° 0.71073 0.71073 1.54184 mation.Comparison of the 1H NMR spectra for compounds Space group P1 : (No. 2) Pca21 (No. 29) P21/c (No. 14) 7a–c and 8a–c suggested that, in solution, compounds 7a–c Z 2 4 2 adopt very diVerent conformations from compounds 8a–c. In m/cm-1 7.1 7.9 78.9 the former series, the presence of large 3JAB coupling Dc/g cm-3 1.47 1.52 1.48 (12.5–12.8 Hz) is indicative of an s-trans conformation; in crystal size/mm 0.1×0.4×0.4 0.35×0.16×0.015 0.05×0.3×0.5 contrast, compounds 8a–c exhibited a significantly smaller 3JAB scan mode v/2h v v 2hmax (°) 60 51.2 150 coupling (4.8–4.9 Hz) suggesting an s-cis conformation which data total 3753 5636 2132 could be stabilised by a close S · · ·N intramolecular contact data unique 3185 1855 1888 (for the solid-state structures of 7b and 8b determined by Xdata observed, ray analysis, see below).In solution, the ethylenic chain in I.2s(I ) 2336 1491 1459 compounds 13a–c and 14a–c retains an all s-trans confor- Rint 0.039 0.074 0.019 mation; this was established by analysis of the coupling absorption correction empiricala numerical empiricala constants 3JBC, 3JDE=13.9–15.1 Hz and 3JAB, 3JCD, 3JEF= transmission 8.0–11.6 Hz.COSEY (1H , 1H) spectra for compounds 13a–c min5max 0.9451.00 0.69050.988 0.3251.00 and 14a–c allowed definitive identification of all the ethylenic no. efined protons. After completion of our work, a similar synthesis of variables 177 160 113 analogues 16a–d was described by Gorgues and co-workers,24k weighting scheme, for which comparable 1H NMR data were obtained, and they A, Bb 0.046, 0.75 0, 2.66 0.108, 3.21 wR(F2), all data 0.073 0.149 0.191 too concluded an all trans configuration in solution.goodness-of-fit 1.05 1.36 1.11 Confirmation of the all s-trans configuration was obtained by R(F), obs.data 0.038 0.056 0.072 X-ray analysis of compound 16a.24k Evidence for the retention Drmax/e A° -3 0.55 0.44 0.89 of the all trans stereochemistry of dialdehyde 10 in the product Drmin/e A° -3 -0.54 -0.37 -0.52 15b obtained therefrom was provided by 1H NMR simulation. The absolute values of proton shifts were determined by a72 y-scans of 2 reflections, TEXSAN software.43 bw-1=s2(F2)+ (AP)2+BP, where P=(Fo2+2Fc2)/3 (1H, 13C) HETCOR and, using literature J values, the spectra J.Mater. Chem., 1998, 8(5), 1173–1184 1175Fig. 1 Molecular structure of 7b showing overlap of adjacent molecules in a stack. Bond distances (A ° ): C(1)–C(4) 1.387, C(4)–C(5) 1.402, C(5)–C(6) 1.384, C(1)–S(1) 1.743, C(1)–S(2) 1.727, S(1)–C(2) 1.757, S(2)–C(3) 1.753, C(2)–C(3) 1.343, mean C–S(Me) 1.813, C(6)–C(N) 1.430, C–N 1.149 (e.s.d. 0.004, for C–S 0.003). a degree of p-delocalisation (D0.02 A ° ) is usual for polyene Fig. 3 (a) Molecular structure of 15b (primed atoms are inversionrelated). Bond distances (A° ): C(1)–C(6) 1.348(9), C(6)–C(7) 1.430(10), chains with an electron-withdrawing dicyanomethylene group C(7)–C(8) 1.369(9), C(8)–C(8¾) 1.417(13), C(1)–S(1) 1.749(7), of one end and an electron-releasing (e.g.amino) substituent C(1)–S(2) 1.769(6), S(1)–C(2) 1.770(6), S(2)–C(3) 1.771(6), at the other end (e.g. compounds 17 and 18).34 1,2-Dithiole C(2)–C(3) 1.332(8). (b) Molecular structure of 15b, side-view, and 1,3-dithiole heterocycles have been shown to produce a showing planarity. similar eVect, e.g. compounds 19 (D=0.02 A ° )35 and 20,36 the latter having the same conjugated path and the same acceptor group as 7b, with the same D value (0.016 A ° ).Molecules in the tron transfer) of adjacent molecules are nearly overlapping crystal of 7b, related via an x translation, form a stack with (Fig. 1). an interplanar separation of ca. 3.4 A ° and a lateral shift of In molecule 8b (Fig. 2) all non-hydrogen atoms lie in one 3.5 A ° , such that the oppositely charged dithiole and dicyanoplane within 0.03 A ° , except the methyl atoms C(4) and C(5) methylene moieties (arising as a result of intramolecular elecwhich are situated at 1.24 and 1.67 A ° , respectively, from this plane (on the same side).The N(1) atom, which is in a synorientation towards the dithiole group, forms a short intramolecular contact of 2.719(6) A ° with S(1) which is substantially less than the sum of their respective van der Waals radii (3.35 A° ).37 This fact, together with p-delocalisation along the C(1)C(6)C(7)N(1) chain, suggests some degree of intramolecular sulfur · · · nitrogen bonding interaction. The only noteworthy intermolecular contact N(2) · · · S(2) (x-1/2, 2-y, z) which is nearly coplanar with the ring and trans to the S(2)–C(3) bond, is not particularly short (3.28 A ° ).The central tetraene moiety of compound 15b adopts an alltrans configuration [Fig. 3(a)]. It is notable that the alternation of bond lengths is smaller (D=0.07 A ° ) than in non-substituted octatetraene (D=0.12 A ° ).33a Molecule 15b lies on a crystallographic inversion centre and has a predominantly planar structure [Fig. 3(b)], distorted by: (i) small twists (5°) around the C(6)–C(7) bond; (ii) folding of the dithiole rings along the N CN NC CN NC O O O N O S S CN CN Ph S S Ph Me S S CN NC 17 20 19 18 S(1) · · · S(2) vectors by 8°; and (iii ) out-of-plane conformation of the methyl groups, i.e. twists around the C(2)–S(3) and C(3)–S(4) bonds by 18 and 64°, respectively.Molecules in the crystal contact in a perpendicular edge-to-face fashion and thus no stacks exist (cf. extended donor 21 which stacks in uniform fashion along the x-axis24j). Fig. 2 Molecular structure of 8b. Bond distances (A° ): S(1)–C(1) 1.739(7), S(1)–C(2) 1.751(7), S(1) · · ·N(1) 2.719(6), S(2)–C(1) 1.741(7), S(2)–C(3) 1.743(8), N(1)–C(8) 1.340(9), C(1)–C(6) 1.376(10), C(6)–C(7) 1.398(10), N(1)–C(7) 1.313(9), C(8)–N(2) 1.148(9); angles (°): C(2)S(1)N(1) 171.4(2), C(7)N(1)C(8) 119.8(6).S S S S R R R R S S S S MeS MeS SMe SMe S S S S 21 R = MeS 22 R = H 24 23 1176 J. Mater. Chem., 1998, 8(5), 1173–1184Fig. 5 Cyclic voltammograms of compounds 7b (- ·-·-·) and 14b (¢¢) an irreversible one-electron reduction wave, to form the radical anion located on the dicyanomethylene or N-cyanoimine group.Within each series of D–p–A systems studied (e.g. compounds 7a–c) there is a small cathodic shift of both the oxidation and the reduction peaks with increasing donor Fig. 4 UV–Visible absorption spectra for compound 14b in various solvents, at 20 °C, demonstrating solvatochromism. Solvents: strength. Similarly, when series 5, 7 and 14 are compared, there CF3CH2OH (¢¢) lmax 556 nm, DMSO (······) lmax 553 nm, CH2Cl2 (- is a significant cathodic shift in the oxidation wave and an ··- ··) lmax 555 nm, MeCN (-- -- -) lmax 533 nm, Et2O (¢¢¢) lmax anodic shift in the reduction wave on increasing the conju- 528 nm, hexane (-·- ·-·- ·) lmax 526 nm.gation length (Fig. 5). The UV and CV data are entirely consistent with an increase in electron delocalisation with Electronic absorption spectra of compounds 5, 7, 8 and 14 increasing conjugated chain length.Furthermore, they confirm that the relative donor and acceptor strenths follow the series: The electronic absorption spectra of compounds 5, 7, 8 and 4,5-dimethyl . 4,5-bis(methylsufanyl) . 4,5-bis(methoxy- 14 are dominated by a broad low-energy band [lmax(MeCN) carbonyl) and dicyanomethylene.N-cyanoimine. 354–533 nm, dependent on substituents and conjugative length The solution redox properties of the bis(1,3-dithiole) donors (Table 2)]. Following precedents for other D–p–A systems, 15a–c are collated in Table 3, along with selected model this band is attributed to a photoinduced intramolecular compounds 21–24 for comparison.For all the new extended electron transfer from the 1,3-dithiol-2-ylidene moiety to the donors, only one redox couple involving a two-electron transfer acceptor fragment. For each series of compounds 5, 7, 8 and is observed [this redox couple could not be resolved into two 14, the variation of donor substitution has a small, but separate couples by: (i) lowering the polarity of the solvent; significant, eVect on the position of the charge-transfer band.(ii ) reducing the scan rate; (iii) lowering the temperature to In all cases, the absorption maxima in the 1,3-dithiole series -78 °C; or (iv) diVerential pulse voltammetry]. It is unclear shift bathochromically with increased donor strength [e.g. whether this wave is the result of two inseparable one-electron lmax(MeCN) 7a 489; 7b 475; 7c 439 nm].Similarly, a comparioxidations, or a concomitant two-electron transfer. In either son of absorption spectra for compounds 5b, 7b and 14b shows case, these data are entirely consistent with previous work that the maxima shift bathochromically with increasing number with vinylogous TTF systems17,24 which has established the of conjugated double bonds [lmax(MeCN) 5b 364; 7b 475; 14b following general trends in the redox properties with increasing 533 nm].The absorption spectra of compounds 14b and 14c conjugative length. There is: (i) a lowering of the first oxidation exhibit marked solvatochromism (exemplified in Fig. 4 for potential (E1) due to the increased electron delocalisation; and, compound 14b).(ii ) a smaller diVerence (DE) between E11/2 and E21/2 (tending to zero as the conjugation length increases), indicative of Cyclic voltammetry of compounds 5, 7, 8, 14 and 15 increased stabilisation of the dicationic state as a result of increased charge separation (and thus reduced on-site The solution redox properties of D–p–A compounds 5, 7, 8 Coulombic repulsion). These observations on the influence of and 14 have been studied by cyclic voltammetry and the results conjugative chain length are shown clearly in a comparison are collated in Table 2.All the new compounds display a of the cyclic voltammograms of compounds 156, 21 and 24 reversible one-electron oxidation wave, attributed to the forma- (Fig. 6). Predictably, compound 15a is the best donor in the tion of the radical cation of the 1,3-dithiole donor moiety, and series due to the presence of the electron releasing methyl substituents on the 1,3-dithiole ring.Table 2 Cyclic voltammetric dataa and electronic absorption maximab for D–p–A compounds 5a–c, 7a–c, 8a–c and 14b–c Table 3 Cyclic voltammetric dataa for extended TTF vinylogues 15a–c, with the data for compounds 1 and 21–24 for comparison Eox/V Ered/V lmax/nm 5a 1.70 -1.67 387 E11/2/V E21/2/V E21/2-E11/2/V 5b 1.76 -1.52 364 5c 2.15 -1.24 354 TTF 1 0.34 0.71 0.37 2217 0.20 0.36 0.16 7a 1.09 -1.18 489 7b 1.14 -1.06 475 2317 0.217 0.223 0.006 24 0.53 0.78 0.25 7c 1.49 -1.01 439 8a 1.25 -1.37 450 2118,24j 0.50 0.63 0.12 15a 0.18b — — 8b 1.17 -1.22 448 8c 1.65 -1.14 426 15b 0.36b — — 15c 0.56b — — 14b 0.73 -0.84 533 14c 0.97 -0.81 492 a10-5 M compound in dry MeCN under argon vs.Ag/AgCl, Pt working and counter electrodes, 20 °C, 100 mV s-1 scan rate. bTwo a10-5 M compound in dry MeCN under argon vs. Ag/AgCl, Pt working and counter electrodes, 20 °C, 100 mV s-1 scan rate. bIn electron redox couple with peaks observed as a single wave, Eox-Ered=56 mV, indicative of two non-interacting redox centres MeCN solution, 20 °C.J. Mater. Chem., 1998, 8(5), 1173–1184 1177Theoretical calculations To gain a deeper understanding of the experimental trends reported above, the molecular structure and electronic properties of the unsubstituted (R=H) compounds 7, 8, 14 and 15 were calculated within the density functional theory (DFT) approach.40 Compared to Hartree–Fock (HF) methods, DFTbased calculations have the advantage of including electron correlation eVects and have been shown to provide more accurate optimised geometries and energetic data.41 All calculations were performed using the B3P86 density functional and the polarised 6-31G* basis set.Molecular structure of 7, 8, 14 and 15 (R=H). The molecular Fig. 6 Cyclic voltammograms of compounds 15b (¢¢), 21 (-- -- -) and 24 (-·- ·) structures of 7 and 8 were optimised both in cis and trans conformations.The minimum energy conformation corre- Table 4 Dipole moment and non-linear optical dataa sponds to the trans orientation for 7 and to the cis structure for 8 in agreement with NMR and X-ray observations. The b(0)/ m.b(0)/ optimised bond lengths and bond angles calculated for these compound l0/nm m/D b/10-30 esu 10-30 esu 10-48 esu structures are shown in Fig. 7. In order to compare the optimised structures with those obtained experimentally, the 7a 489 8.8 31 13 112 average deviations between the experimental X-ray data 7b 475 6.9 37 15 105 7c 439 6.8 24 12 85 reported for 7b and 8b and the theoretical structures obtained 14b 556 — m.b=4554 — 1170 for unsubstituted 7 and 8 were calculated for the bond lengths, d : (R), and the bond angles, d : (a). The deviations were found to aMeasured in CHCl3.Relative errors: m,3%; b,10%; b(0),10%. be very small both for 7 [d : (R)=0.012 A ° , d : (a)=0.7°] and 8 [d : (R)=0.009 A ° , d : (a)=0.5°], demonstrating the agreement Non-linear optical properties between theory and experiment.The cis conformer of 7 was found to be destabilised by The non-linear optical properties of compounds 7a–c and 14b 7.91 kcal mol-1 with respect to the trans structure due to the were determined using the EFISH technique performed at short S(2) · · · C(7) and S(2) · · ·N(1) contacts resulting from the 1.34 mm and the data are presented in Table 4. From experimenrotation around C(4)–C(5) [see Fig. 7(a)]. To alleviate these tal b values at 1.34 mm it is possible to infer ‘static’ b(0) values contacts, the S(2)–C(1)–C(4), C(1)–C(4)–C(5), C(4)–C(5)– using a two-level dispersion model,38 which can be considered C(6) and C(5)–C(6)–C(7) bond angles widen to 129.0, 134.9, as valid in the present case of unidimensional electronic charge- 136.9 and 128.5°, respectively.These values are very much transfer molecules:39 larger than those found for the trans conformer [see Fig. 7(b)] indicating the strain present in the cis conformer. b= 3b2 2mW 3 W 4 (W 2-b2v2)(W2-4b2v2) fDm In contrast to 7, the cis conformer of 8 is calculated to be more stable than the trans orientation by 3.85 kcal mol-1. The optimised distance between S(1) and N(1) in the cis = W 4 (W 2-b2v2)(W2-4b2v2) b(0) (1) orientation is 2.722 A° , in very good agreement with the observed X-ray value of 2.719(6) A ° .This short intramolecular where contact is stabilised by the opposite charges borne by S(1) and N(1) (see Fig. 8), which give rise to a bonding electrostatic- b(0)=b0= 3b2 2m fDm W 3 (2) type interaction. For the trans conformer, both sulfur atoms present net atomic charges of +0.34e.For the preferred cis W being the energy of the charge transfer electronic transition, conformer, the S(1) atom augments its charge to +0.43e and f the corresponding oscillator strength, Dm=m1-m0 (where m1 is the dipole moment of the first excited state). Compounds 7a–c exhibit moderate non-linear optical properties [cf. the relevant application parameter is m.b(0), the standard value for the ‘classical’ NLO dye DR1 is ca. 500×10-48 esu] (Table 4). The dependence of b(0) upon the nature of R substitution is weak, m.b(0) being slightly smaller for the weakly electron donating CO2Me substituent. The b(0) values are comparable to those of p-nitroaniline derivatives. The quadratic hyperpolarisability dramatically increases when adding two double bonds, leading to m.b(0) values that are double those of the standard dye DR1.Although the dipole moment of 14b could not be measured (due to a moderate solubility in non-polar solvents), m was estimated to be ca. 7 D. This enhancement of m.b(0) is strongly correlated with the increase in electron delocalisation with increasing the conjugated length. The strong red-shift of the maximum absorption wavelength lmax corresponds to a significant decrease of W.The large solvatochromism of compound 14b indicates a high Dm value, and the strong hyperchromic eVect observed when increasing the number of double bonds corresponds to a high oscillator strength f. All these factors result in the observed enhancement of m.b(0) (by a factor of two) for Fig. 7 B3P86/6-31G*-optimised minimum energy structures of 7 (trans) and 8 (cis). (a) Bond lengths in A° . ( b) Bond angles in degrees compound 14b. 1178 J. Mater. Chem., 1998, 8(5), 1173–1184consequence of the magnitude of the electron transfer between the donor and the acceptor units. Mulliken population analysis based on B3P86/6-31G* calculations predicts that the net charge of the dithiole ring decreases in passing from 2 (+0.28e) to 7 (+0.17e) and to 14 (+0.11e).The charge transfer thus decreases as the length of the conjugated spacer increases, justifying the increase of the C(1)–S bond lengths and of the single–double bond alternation along the series 2,7,14. However, it should be noted that although the charge transfer decreases along this series, the dipole moment increases due to the separation of the donor and the acceptor moieties. The dipole moments calculated at the B3P86/6-31G* level are 7.9 D (2),10.2 D (7),13.7 D (14).Although these values overestimate the experimental data for compounds 7 (see Table 4), they can be used as a good estimate of the variation of the dipole moment as the length of the conjugated spacer Fig. 8 B3P86/6-31G* net atomic charges (in e) for cis and trans increases. conformations of 8 (top) and for trans-7 (bottom) Compound 15 presents mean C(1)–S bond lengths of 1.771 A ° and a mean alternation in the octatetraene spacer of 0.067 A ° . These values are in good agreement with the experimental Xray values (1.759 and 0.07 A° , respectively) and are larger than those theoretically obtained for 14 (1.760 and 0.047 A ° ).Despite the absence of charge transfer, the alternation of the conjugated spacer in 15 is significantly shorter than that calculated for the octatetraene molecule (0.101 A ° ) using the same theoretical approach. The terminal C(1)–C(6) and C(6)–C(7) bonds of 15 present the largest diVerences with the equivalent bonds of octatetraene (see Fig. 9). Electronic structure. We turn now to discuss the redox properties on the basis of molecular orbital energies and topologies. Table 5 summarises the energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of 7, 8, 14 and 15 and of selected compounds TTF (1), 2, 22 and 23 for comparison. Table 5 B3P86/6-31G* molecular orbital energies e eHOMO/ eLUMO/ eHOMO/ eLUMO/ compound eV eV compound eV eV 2 -7.07 -2.94 TTF 1 -5.09 -1.54 7 -6.63 -3.37 22 -4.99 -1.35 7a -6.37 -3.20 23 -4.93 -1.82 7c -6.92 -3.53 15 -4.89 -2.12 8 -6.60 -2.95 14 -6.11 -3.60 Fig. 9 B3P86/6-31G*-optimised bond lengths (in A ° ) of 2, 14, 15 and octatetraene. 2 exhibits C2v symmetry. 15 and octatetraene exhibit C2h symmetry. faces the negatively charged N(1) atom (-0.51e). The adoption of a cis orientation by compounds 8 thus results not only in an attractive coulombic interaction, but also determines a more eVective charge transfer between the donor dithiole ring and the acceptor cyanoimine unit. It should be also stressed that, for 8, the adoption of the cis conformation causes no special distortion of the bond angles [see Fig. 7(b)] as was the case for cis-7. Fig. 9 shows the bond lengths calculated for unsubstituted 14 and 15 in their most stable all-trans conformation; the values obtained for 2 and for octatetraene are included for comparison. As the length of the conjugated linker along the series 2, 7, 14 increases (see Fig. 7 and 9), the mean length of the C(1)–S bonds becomes longer passing from 1.743 A ° (2) to 1.754 A ° (7) and to 1.760 A °(14).This evolution is accompanied by an increase of the mean alternation between single and double bonds in the spacer unit which varies from Fig. 10 Electronic density contours of the HOMO and LUMO of 7 0.039 A° for 7 to 0.047 A° for 14. Both geometrical trends are a J. Mater. Chem., 1998, 8(5), 1173–1184 1179The topology of these orbitals is exemplified in Fig. 10 for Conclusions compound 7. The HOMO resides mainly on the 1,3-dithiol-2- A series of novel highly-conjugated donor–p–acceptor chromo- ylidene group while the LUMO spreads over the phores 5a–c, 7a–c, 8a–c, 13a–c and 14b–c have been syn- CnC–CnC(CN)2 unit. Similar atomic orbital compositions thesised, in which the donor units (substituted 1,3-dithioles) are found for compounds 2, 8 and 14.are separated from dicyanomethylene and N-cyanoimine From a MO standpoint, oxidation implies the extraction of acceptor groups by an ethylenic or oligoethylenic linker (one, an electron from the HOMO, and reduction implies the two and four conjugated double bonds). Extended tetrathiaful- introduction of an electron into the LUMO. More positive valene derivatives 15a–c have also been synthesised.The oxidation potentials are therefore to be expected for comelectronic spectra, redox properties, non-linear optical proper- pounds with lower energy HOMOs and more negative ties and X-ray crystal structures of representative derivatives reduction potentials for compounds with higher energy have been studied. These experimental data are supported by LUMOs.This trend is observed when comparing the calculated theoretical calculations. A broad low-energy intramolecular MO energies (Table 5) with the redox potentials obtained charge-transfer band observed for compounds 5, 7, 8 and 14 experimentally by CV (Tables 2 and 3). For the D–p–A shifts bathochromically with increasing donor strength of the compounds, the HOMO increases in energy and the LUMO dithiole ring, and with increasing length of conjugation between decreases in energy as the length of the conjugated p spacer the donor and acceptor moieties. Cyclic voltammetric data increases along the series 2, 7, 14.The destabilisation of the establish that compounds 5, 7, 8 and 14 undergo a reversible HOMO accounts for the cathodic shift of the oxidation one-electron oxidation, and an irreversible one-electron potential and the stabilisation of the LUMO justifies the reduction, to form the radical cation and radical anion species, anodic shift of the reduction potential along that series.The respectively. For the bis(dithiole) donors 15a–c a single two- eVect of substituents has been studied for compound 7.As electron redox wave is observed. Moderate NLO properties the donor strength of the substituent increases [7c (R= are observed for compounds 7a–c [m.b(0) 85–112×10-48 esu] CO2Me),7 (R=H),7a (R=Me)], both the energy of the whereas for the more extensively conjugated compound 14b, HOMO [-6.92 eV,-6.63 eV,-6.37 eV] and the LUMO the value is increased to m.b(0) 1170×10-48 esu.The minimum [-3.53 eV,-3.37 eV,-3.20 eV] increase accounting for energy conformations predicted for 7 and 8 are in agreement the cathodic shift of the oxidation and reduction potentials with X-ray crystal structures and solution NMR data. These along this series. The destabilisation eVect is more important results should stimulate further studies on the use of 1,3- for the HOMO in agreement with the larger cathodic shifts dithiol-2-ylidene units as electron donor components in D–p–A observed for the oxidation potential (see Table 2). materials, which by virtue of intramolecular charge-transfer The relative energies of the LUMO of 7 (-3.37 eV) and 8 will possess interesting electronic, optical, non-linear optical (-2.95 eV) confirm the higher acceptor capability of the diand structural properties.cyanomethylene group in accord with CV data. The almost identical energies obtained for the HOMO of 7 (-6.63 eV) and 8 (-6.60 eV) suggest, however, that similar donor properties should be expected for both compounds. This prediction Experimental contrasts with the lower oxidation potentials measured for General methods compounds 7. The additional factor that should be taken into account to explain the experimental trend is the diVerent 1H NMR Spectra were obtained on a Bruker AC 250 specconformations displayed by compounds 7 and 8.As mentioned trometer operating at 250.134 MHz. 13C NMR Spectra were above, the cis conformation adopted by 8 allows for a more obtained on a Varian 400 spectrometer operating at eVective charge transfer due to the S(1) · · · N(1) bonding 100.581 MHz.Mass spectra were recorded on a VG7070E interaction. The dithiole ring exhibits a net charge of +0.23e spectrometer operating at 70 eV. IR Spectra were recorded on in 8 compared to the charge of +0.17e calculated for 7. The a Perkin-Elmer 1615 FTIR spectrometer operated from a greater charge defect accumulated by that ring in 8 makes it Grams Analyst 1600.UV–VIS Spectra were obtained on a harder to extract an electron upon oxidation, since it is mainly Kontron Uvicon 930 spectrophotometer using quartz cells; removed from the dithiole moiety, thus leading to a higher extinction coeYcients (e) are quoted in M-1 cm-1. Melting oxidation potential. points were obtained on a Kofler hot-stage microscope appar- The atomic orbital composition of the HOMO and the atus and are uncorrected.Cyclic voltammetric data were LUMO of D–p–A compounds suggests that the lowest-energy obtained on a BAS 50W electrochemical analyser (1×10-5 M HOMO�LUMO electronic transition implies an electron solution of donor in acetonitrile under argon, 1×10-1 M transfer from the dithiole environment to the acceptor part of Bu4NClO4 supporting electrolyte, platinum working and counthe molecule.This supports the intramolecular electron transfer ter electrodes, Ag/AgCl reference electrode, 20 °C). Column character of the first absorption band observed in the electronic chromatography was performed on Merck silica gel (70–230 spectra. The HOMO–LUMO energy gap decreases with the mesh), unless otherwise stated, and solvents were distilled prior length of the conjugated spacer (2.7.14) and with the to use.All reagents were of commercial quality and used as donor strength of the substituents (7c.7.7a) (see Table 5). supplied unless otherwise stated; solvents were dried where These trends justify the bathochromic shifts observed expernecessary using standard procedures.imentally along those series (see Table 2). The smaller values of lmax measured for compounds 8 with respect to 7 are due to the higher energy of the LUMO of 8 which enlarges the General procedure for compounds 4a–c HOMO–LUMO gap. To a stirred solution of thiones 3a,13 3b14 or 3c15 (30 mmol) The HOMO of the bis(dithiole) compounds 22, 23 and 15 in dry dichloromethane (100 ml) was added methyl trifluoro- spreads over the whole molecule involving both dithiole moietmethanesulfonate (3.5 ml, 30 mmol).The resultant mixture ies and the central polyenic chain. This determines that its was stirred under an argon atmosphere for 2 h at 20 °C energy slightly increases with the length of the chain as is the whereupon addition of anhydrous diethyl ether (100 ml) pre- case for polyenes.As a consequence, the first oxidation potencipitated a solid, which was filtered, washed with anhydrous tial lowers with increasing the conjugate length (see Table 3 diethyl ether and dried to aVord the products. The products and Fig. 6). The LUMO decreases in energy more rapidly are moisture sensitive, but may be stored under argon for at along the series TTF, 22, 23, 15 as it is localised primarily on the conjugated chain. least 3 months.The following were obtained. 1180 J. Mater. Chem., 1998, 8(5), 1173–11844,5-Dimethyl-2-methylsulfanyl-1,3-dithiolium triflate 4a. m/z (CI) 221 (M++1, 25%), 238 (M++NH4, 100%); dH(CDCl3) 7.35 (HB, d, JAB 12.8), 6.54 (HA, d, JAB 12.8), 2.15 (9.65 g, 96%) White solid, mp 71 °C (Analysis found: C, 26.0; H, 2.9; C7H9F3O3S4 requires: C, 25.8; H, 2.8%); dH[(CD3)2CO] (3H, s), 2.13 (3H, s); dC(CDCl3) 167.3, 151.0, 127.5, 127.2, 116.0, 113.9, 106.1, 68.5, 13.7, 13.3; nmax(KBr)/cm-1 2208 and 2200 3.27 (3H, s), 2.72 (6H, s).(both CoN), 1540 (CnC); lmax(MeCN)/nm (e) 489 (4.2×104), 467 (3.5×104), 249 (7.4×103). 2,4,5-Tris(methylsulfanyl )-1,3-dithiolium triflate 4b. (11.68 g, 97%) Yellow solid, mp 75 °C (Analysis found: C, 21.5; H, 2.4; 1-[4,5-Bis(methylsulfanyl )-1,3-dithiol-2-ylidene]-3,3- C7H9F3O3S6 requires: C, 21.5; H, 2.3%); dH[(CD3)2CO] 3.34 dicyanoprop-2-ene 7b.(504 mg, 71%) Red solid, mp 149–150 °C (3H, s), 2.83 (6H, s). (Analysis found: C, 42.2; H, 2.8; N, 9.8; C10H8N2S4 requires: C, 42.2; H, 2.8; N, 9.9%); m/z (CI) 285 (M++1, 100%), 302 4,5-Bis(methoxycarbonyl )-2-methylsulfanyl-1,3-dithiolium (M++NH4, 12%); dH(CDCl3) 7.30 (HB, d, JAB 12.7), 6.65 (HA, triflate 4c.(11.88 g, 93%) White solid, mp 97 °C (Analysis d, JAB 12.7), 2.47 (s, 3H), 2.46 (s, 3H); dC(CDCl3) 164.2, 150.8, found: C, 26.0; H, 2.2; C9H9F3O7S4 requires: C, 26.1; H, 2.2%); 130.8, 130.3, 115.1, 113.1, 108.0, 71.7, 19.2, 19.1; nmax(KBr)/cm-1 dH[(CD3)2CO] 4.04 (6H, s), 3.44 (3H, s). 2210 (CoN), 2198 (CoN), 1554 (CnC); lmax(MeCN)/nm (e) 475 (5.3×104), 318 (1.0×104), 244 (1.0×104). A crystal suitable General procedure for compounds 5a–c for X-ray analysis was grown by slow evaporation of its To a stirred suspension of salt 4 (15 mmol) in dry propan-2- CH2Cl2 solution. ol (25 ml ) at 20 °C under argon was first added malononitrile (1.1 g, 16.8 mmol) followed by dry pyridine (3 ml, excess).After 1-[4,5-Bis(methoxycarbonyl )-1,3-dithiol-2-ylidene]-3,3- stirring for 3 h, water (150 ml) was added and the mixture dicyanoprop-2-ene 7c. (492 mg, 64%) Orange solid, mp extracted into CH2Cl2 (3×75 ml) and the organic phase 202–203 °C (sublimes from ca. 150 °C) (Analysis found: C, 46.9; washed with water (2×200 ml).After drying (MgSO4) and H, 2.7; N, 9.0; C12H8N2O4S2 requires: C, 46.8; H, 2.6; N, evaporation in vacuo, column chromatography eluting with 9.1%); m/z (CI) 309 (M++1, 80%), 326 (M++NH4, 100%); CH2Cl2, and, if necessary, recrystallisation from CHCl3 the dH(CDCl3) 7.32 (HB, d, JAB 12.5), 6.60 (HA, d, JAB 12.5), 3.92 following were obtained. (6H, s); nmax(KBr)/cm-1 2218 (CoN), 2208 (CoN), 1707 [C(nO)–O–]; lmax(MeCN)/nm (e) 439 (2.5×104), 241 (4,5-Dimethyl-1,3-dithiol-2-ylidene)dicyanomethane 5a.(5.8×103). (2.04 g, 67%) Tan needles, mp 228–229 °C (sublimes from ca. 150 °C) (Analysis found: C, 50.2; H, 2.9; N, 14.2; C8H6N2S2 General procedure for compounds 8a–c requires: C, 49.5; H, 3.1; N, 14.4%); m/z (EI) 194 (M+, 100%); To a stirred solution of aldehyde 6a17, 6b18 or 6c17 (3 mmol) m/z (CI) 195 (M++1, 25%), 212 (M++NH4, 100%); in dry CH2Cl2 (25 ml ) under argon at 20 °C were added dH(CDCl3) 2.21 (6H, s); dC[(CDCl2)2] 180.9, 129.8, 114.4, 60.7, sequentially (i) titanium tetrachloride (3.3 ml, 3.3 mmol, 1 M in 14.0; nmax(KBr)/cm-1 2205 (CoN); lmax(MeCN)/nm (e) 387 CH2Cl2), (ii) N,N-bis(trimethylsilyl)carbodiimide (0.75 ml, (1.3×104), 370 (1.5×404), 233 (4.8×104). 3.3 mmol) and (iii) dry pyridine (1 ml, excess) and the mixture was stirred for a further 48 h. After dilution with CH2Cl2 [4,5-Bis(methylsufanyl )-1,3-dithiol-2-ylidene]dicyano- (250 ml) the mixture was washed with water (3×100 ml). After methane 5b. (2.36 g, 61%) Pale yellow solid, mp 100–101 °C drying (MgSO4), the solvent was evaporated in vacuo and the (Analysis found: C, 37.4; H, 2.4; N, 11.0; C8H6N2S4 requires: residue was chromatographed eluting with ethyl acetate to C, 37.2; H, 2.3; N, 10.8%); m/z (EI) 258 (M+, 100%); m/z (CI) aVord the products.The following were thus obtained. 259 (M++1, 50%), 276 (M++NH4, 100%); dH(CDCl3) 2.52 (6H, s); nmax(KBr)/cm-1 2207; lmax(MeCN)/nm (e) 364 1-(N-Cyanoimino)-2-(4,5-dimethyl-1,3-dithiol-2- (1.3×104), 353 (1.6×104), 214 (9.2×103).ylidene)ethane 8a. (459 mg, 78%) Orange solid, mp 181–182 °C (sublimes from ca. 130 °C) (Analysis found: C, 48.8; H, 3.8; N, [4,5-Bis(methoxycarbonyl )-1,3-dithiol-2-ylidene]dicyano- 14.3; C8H8N2S2 requires: C, 49.0; H, 4.1; N, 14.3%); m/z (CI) methane 5c. (2.34 g, 65%) Cream solid, mp 104–105 °C 197 (M++1, 100%); dH(CDCl3) 8.24 (HB, d, JAB 4.9), 6.39 (Analysis found: C, 42.7; H, 2.1; N, 10.0; C10H6N2O4S2 requires: (HA, d, JAB 4.9), 2.23 (3H, s), 2.22 ((3H, s); dC(CDCl3) 167.6, C, 42.5; H, 2.1; N, 9.9%); m/z (EI) 282 (M+, 100%); m/z (CI) 166.3, 131.9, 126.9, 118.8, 103.4, 13.5, 13.0; nmax(KBr)/cm-1 283 (M++1, 40%); dH(CDCl3) 3.96 (6H, s); dC[(CD3)2CO] 2155 (CoN), 1542 (CnC), 1457 (CnN); lmax(MeCN)/nm (e) 182.4, 161.6, 138.2, 116.7, 67.4, 59.4, 57.3; nmax(KBr)/cm-1 2207 450 (5.0×104), 432 (3.7×104), 236 (9.7×103).(CoN), 1710 [C(nO)–O–]; lmax(MeCN)/nm (e) 354 (2.3×104), 214 (1.5×104). 1-(N-Cyanoimino)-2-[4,5-bis(methylsufanyl )-1,3-dithiol-2- ylidene]ethane 8b. (660 mg, 85%) Orange solid, mp 127–128 °C General procedure for compounds 7a–c (Analysis found: C, 37.0; H, 2.9; N, 10.9; C8H8N2S4 requires: To a stirred solution of aldehyde 6a,17 6b18 or 6c17 (2.5 mmol) C, 36.9; H, 3.1; N, 10.7%); m/z (CI) 261 (M++1, 100%); in dry CH2Cl2 (50 ml ) der argon at 20 °C were added dH(CDCl3) 8.32 (HB, d, JAB 4.8), 6.48 (HA, d, JAB 4.8), 2.56 sequentially: (i) malononitrile (248 mg, 3.75 mmol), (ii) tit- (3H, s), 2.51 (3H, s); dC(CDCl3) 167.3, 166.1, 134.9, 129.5, 117.9, anium tetrachloride (3.75 ml, 3.75 mol, 1 M in CH2Cl2) and 105.4, 19.2, 19.0; nmax(KBr)/cm-1 2161 (CoN), 1540 (CnC), (iii ) dry pyridine (1 ml, excess) and the mixture was then 1455 (CnN); lmax(MeCN)/nm (e) 448 (1.3×104), 307 refluxed for 24 h.After cooling, the mixture was diluted with (2.5×103), 201 (8.1×103). A crystal suitable for X-ray analysis CH2Cl2 (250 cm3) and washed with water (3×100 ml).After was grown by slow evaporation of its CH2Cl2 solution. drying (MgSO4), the solvent was evaporated in vacuo and the residue was chromatographed eluting with CH2Cl2 to aVord 1-(N-Cyanoimino)-2-[4,5-Bis(methoxycarbonyl )-1,3-dithiolthe products. The following were obtained. 2-ylidene]ethane 8c. (681 mg, 80%) Bright yellow solid, mp 156–157 °C (Analysis found: C, 42.0; H, 2.7; N, 10.2; C10H8N2O4S2 requires: C, 42.2; H, 2.8; N, 9.9%); m/z (CI) 261 1-(4,5-Dimethyl-1,3-dithiol-2-ylidene)-3,3-dicyanoprop-2-ene 7a.(358 mg, 65%) Red solid, mp 222–223 °C (sublimes from (M++1, 100%); dH(CDCl3) 8.45 (HB, d, JAB 4.9), 6.59 (HA, d, JAB 4.9), 3.95 (3H, s), 3.93 (3H, s); nmax(KBr)/cm-1 2189 ca. 185 °C) (Analysis found: C, 54.2; H, 3.6; N, 12.9; C10H8N2S2 requires: C, 54.5; H, 3.7; N, 12.7%); m/z (EI) 220 (M+, 100%); (CoN), 2169 (CoN), 1733 and 1710 [both C(nO)–O], 1575 J.Mater. Chem., 1998, 8(5), 1173–1184 1181and 1559 (both CnC), 1471 (CnN); lmax(MeCN)/nm (e) 426 14.1), 6.65 (HE, dd, JED 14.1, JEF 11.9), 6.55 (HB, dd, JBA 11.6, JBC 13.9), 6.24 (HA, d, JAB 11.6), 6.18 (HC, dd, JCB 13.9, JCD (3.5×104), 414 (3.6×104), 227 (1.3×104). 11.5), 2.45 (3H, s), 2.43 (3H, s); nmax(KBr)/cm-1 2215 (CoN), General procedure for compounds 13a–c 1581 (CnC); lmax(MeCN)/nm (e) 533 (2.3×104), 326 (6.8×103), 264 (6.2×103). To a stirred solution of Wittig reagent 11a,17 11b18 or 11c23 (1.5 mmol) and dialdehyde 1021 (1.5 mmol) in dry THF (50 ml ) (E,E)-1-[4,5-Bis(methoxycarbonyl )-1,3-dithiol-2-ylidene]- under argon at 20 °C was added dry triethylamine (1 ml, 7,7-dicyanohepta-2,4,6-triene 14c.Eluting with CH2Cl2 excess) and stirring was continued for 16 h. After evaporation (219 mg, 87%) as a deep red solid, mp 213–214 °C (Analysis of the solvent in vacuo, the residue was extracted with CH2Cl2 found: C, 53.4; H, 3.5; N, 7.6; C16H12N2O4S2 requires: C, 53.3; (250 ml) and washed with water (3×100 ml). The organic H, 3.3; N, 7.7%); m/z (CI) 361 (M++1, 100%); dH(CDCl3) layer was dried (MgSO4) and the solvent evaporated in vacuo. 7.39 (HF, d, JEF 12.0), 6.92 (HD, dd, JDC 11.6, JDE 14.1), 6.67 Purification of the products was achieved by column chroma- (HE, dd, JED 14.1, JEF 12.0), 6.50 (HB, dd, JBA 11.5, JBC 13.9), tography. The following were thus obtained. 6.22 (HA, d, JAB 11.5), 6.21 (HC, dd, JCB 13.9, JCD 11.6), 3.87 (6H, s); dC(CDCl3) 159.1, 159.0, 158.8, 147.9, 142.8, 138.8, 133.0, (E,E)-6-(4,5-Dimethyl-1,3-dithiol-2-ylidene)hexa-2,4-dienal 131.1, 127.3, 125.1, 114.0, 112.1, 109.7, 79.8, 53.8, 53.7; 13a.Elution with CH2Cl2 (150 mg, 45%) as a red solid, mp nmax(KBr)/cm-1 2217 (CoN), 1717 and 1700 [both 108–110 °C (Analysis found: C, 59.0; H, 5.4; C11H12OS2 C(nO)–O], 1566 (CnC); lmax(MeCN)/nm (e) 492 (7.5×104), requires: C, 58.8; H, 5.4%); m/z (DCI) 225 (M++1, 100%); 302 (1.0×104), 252 (1.0×104). dH(CDCl3), 9.50 (HF, d, JEF 8.1), 7.14 (HD, dd, JDC 11.5, JDE 15.0), 6.57 (HB, dd, JBA 12.0, JBC 11.2)., 6.21–6.02 (HA, HC, (E,E)-1,6-Bis(4,5-dimethyl-1,3-dithiol-2-ylidene)hexa-2,4- HE, m); nmax(KBr)/cm-1 1667 (CnO) 1603, 1567, 1501 (all diene 15a CnC); lmax(MeCN)/nm (e) 451 (1.5×104), 280 (9.9×103), 229 (6.4×104).To a solution of Wittig reagent 11a17 (410 mg, 0.9 mmol) and aldehyde 13a (50 mg, 0.23 mmol) in dry THF (50 ml ) at (E,E)-[4,5-Bis(methylsulfanyl )-1,3-dithiol-2-ylidene]hexa- -78 °C was added LDA (1 M in cyclohexane, 0.6 ml, 0.9 mmol) 2,4-dienal 13b. Elution with CH2Cl2 (341 mg, 79%) as a deep and the solution allowed to attain room temperature over red solid, mp 95–96 °C (Analysis found: C, 45.8; H, 4.4; 16 h.The solvent was evaporated and the residue extracted C11H12OS4 requires: C, 45.8; H, 4.2%); m/z (CI) 289 (M++1, into toluene (100 ml), washed with water (100 ml) and the 100%); dH(CDCl3) 9.52 (HF, d, JEF 8.1), 7.12 (HD, dd, JDC organic phase dried (MgSO4). After evaporation of the solvent, 11.1, JDE 15.0), 6.52 (HB, dd, JBA 11.6, JBC 14.1), 6.20 (HC, dd, the residue was chromatographed (neutral alumina, 70–230 JCB 14.1, JCD 11.1), 6.13 (HA, d, JAB 11.6), 6.09 (HE, dd, JED mesh) eluting with hexane–toluene (651 v/v) to aVord com- 15.0, JEF 8.1), 2.41 (3H, s), 2.40 (3H, s); dC(CDCl3) 193.2, 152.2, pound 15a as a black solid (30 mg, 40%); mp 170–173 °C 143.3, 137.5, 129.6, 127.8, 126.7, 125.4, 113.2, 19.0, 18.9; (Analysis found: C, 57.0; H, 5.3; C14H18S4 requires: C, 56.8; H, nmax(KBr)/cm-1 1670 (CnO), 1595 and 1573 (both CnC); 5.3%); m/z (DCI) 339 (M++1, 100%); dH(CDCl3) 6.00–5.98 lmax(MeCN)/nm (e) 438 (2.1×104), 293 (7.6×103), 229 (6H, m), 1.92 (6H, s) 1.89 (6H, s); lmax(MeCN)/nm (e) 476 (4.4×103).(2.9×104), 452 (2.0×104), 270 (9.9×103), 215 (6.4×103).(E,E)-6-[4,5-Bis(methoxycarbonyl )-1,3-dithiol-2-ylidene]- General procedure for compounds 15b–c hexa-2,4-dienal 13c. Initial elution with CH2Cl2 aVorded compound 15c (108 mg, 14%); continued elution with To a stirred solution of Wittig reagent 11c23 or 11d28 (2.0 mmol) CH2Cl2–acetone mixture (1051 v/v) aVorded the product 13c and dialdehyde 1021 (0.9 mmol) in dry THF (50 ml ) under (252 mg, 54%) as an orange solid, mp 147–148 °C (Analysis argon at 20 °C was added dry triethylamine (1.5 ml, excess) found: C, 51.3; H, 3.7; C13H12O5S2 requires: C, 50.0; H, 3.9%); and stirring was continued for 16 h.After evaporation of the m/z (CI) 313 (M++1, 100%); dH(CDCl3) 9.55 (HF, d, JEF 8.0), solvent in vacuo the residue was chromatographed to aVord 7.11 (HD, dd, JDE 15.1, JDC 11.1), 6.47 (HB, dd, JBA 11.2, JBC the products.The following were thus obtained. 14.3), 6.25 (HC, dd, JCB 14.3, JCD 11.1), 6.16 (HA, d, JAB 11.2), 6.10 (HE, dd, JED 15.1, JEF 8.0), 3.86 (6H, s); nmax(KBr)/cm-1 (E,E)-1,6-Bis[4,5-bis(methylsulfanyl )-1,3-dithiol-2- 1730 and 1702 [both C(nO)–O], 1664 (CnO), 1603 (CnC), ylidene]hexa-2,4-diene 15b. Elution with CH2Cl2–hexane (151 1581 (CnC); lmax(MeCN)/nm (e) 410 (2.9×104), 264 v/v) (285 mg, 68%) as a dark orange solid, mp 165–167 °C (8.2×103), 229 (7.8×103).(Analysis found: C, 41.0; H, 4.0; C16H18S8 requires: C, 41.2; H, 3.9%); m/z (CI) 467 (M++1, 100%); dH(CDCl3) 6.05–5.85 General procedure for compounds 14b–c (6H, m), 2.34 (6H, s), 2.32 (6H, s); dC(CDCl3) 132.1, 129.5, 129.0, 127.8, 126.6, 125.7, 125.5, 124.4, 124.3, 115.3, 115.1, 111.1, To a stirred solution of aldehyde 13b–c (0.7 mmol) in dry 18.9, 18.8; lmax(MeCN)/nm (e) 456 (2.6×104), 430 (2.2×104), CH2Cl2 (50 ml ) under argon at 20 °C were added sequentially: 273 (8.5×103), 213 (8.6×103). A crystal suitable for X-ray (i) malononitrile (66 mg, 1 mmol), (ii ) titanium tetrachloride analysis was grown by slow evaporation of its MeCN solution. (1.0 ml, 0.75 mol, 1 M in CH2Cl2) and (iii) dry pyridine (1 ml, Continued elution with CH2Cl2 aVorded compound 13b excess) and the mixture was then refluxed for 24 h.After (47 mg, 18%). cooling, the mixture was diluted with CH2Cl2 (250 ml) and washed with water (3×100 ml). After drying (MgSO4), the (E,E)-1,6-Bis[4,5-bis(methoxycarbonyl )-1,3-dithiol-2- solvent was evaporated in vacuo and the residue was chromatoylidene] hexa-2,4-diene 15c.Elution with CH2Cl2 (310 mg, graphed to aVord the products. The following were thus 66%) as a dark orange solid, mp 186–188 °C (Analysis found: obtained. C, 46.5; H, 3.6; C20H18O8S4 requires: C, 46.7; H, 3.5%); m/z (CI) 515 (M++1, 100%); dH(CDCl3) 6.05–5.97 (6H, m), 3.83 (E,E)-1-[4,5-Bis(methylsulfanyl )-1,3-dithiol-2-ylidene]-7,7- dicyanohepta-2,4,6-triene 14b.Eluting with CH2Cl2–hexane (6H, s) 3.81 (6H, s); nmax(KBr)/cm-1 1749, 1730 and 1702 [all C(nO)–O], 1598 and 1563 (both CnC); lmax(MeCN)/nm (e) (251 v/v) (101 mg, 43%) as a deep red solid, mp 160–162 °C (Analysis found: C, 50.1; H, 3.7; N, 8.2; C14H12N2S4 requires: 433 (9.6×104), 410 (8.5×104), 388 (5.0×104), 239 (1.5×104).Continued elution with CH2Cl2–acetone (1051 v/v) aVorded C, 50.0; H, 3.6; N, 8.3%); m/z (CI) 337 (M++1, 100%; dH(CDCl3) 7.42 (HF, d, JEF 11.9), 6.95 (HD, dd, JDC 11.5, JDE compound 13c (40 mg, 14%). 1182 J. Mater. Chem., 1998, 8(5), 1173–1184Chem., 1995; 5, 365; (e) T. J. Marks and M. A. Ratner, Angew. X-Ray crystallography Chem., Int. Ed. Engl., 1995, 34, 155.Single-crystal X-ray diVraction experiments were carried out 2 Reviews: (a) M. Narita and C. V. Pittman, Synthesis, 1976, 489; (b) A. Krief, T etrahedron, 1986, 42, 1237; (c) G. Schukat, A. M. on a Rigaku AFC6S 4-circle diVractometer (7b, 15b) or a Richter and E. Fangha�nel, Sulfur Rep., 1987, 7, 155; (d) G. Schukat Siemens 3-circle SMART diVractometer with a CCD area and E.Fangha�nel, Sulfur Rep., 1993, 13, 254; (e) T. K. Hansen and detector (8b), using graphite monochromators and Oxford J. Becher, Adv. Mater., 1993, 5, 288. Cryosystems open-flow N2 gas cooling devices. The structures 3 R. Gompper, H.-U. Wagner and E. Kutter, Chem. Ber., 1968, 101, were solved by direct methods and refined by full-matrix least 4123. squares against F2 on all data, using SHELXTL software.42 4 H.E. Katz, K. D. Singer, J. E. Sohn, C. W. Dirk, L. A. King and H. M. Gordon, J. Am. Chem. Soc., 1987, 109, 6561. Non-H atoms were refined anisotropically; all H atoms in 7b 5 (a) M. Blanchard-Desce, I. Ledoux, J.-M. Lehn, J. Malthete and 15b were refined isotropically; in 8b methyl groups were and J. Zyss, J. Chem. Soc., Chem. Commun., 1988, 737; refined as rigid bodies, other H atoms were treated as ‘riding’.(b) M. Barzoukas, M. Blanchard-Desce, D. Josse, J.-M. Lehn and Highest peaks of the residual electron density in all structures J. Zyss, Chem. Phys., 1989, 133, 323. occur near sulfur atoms. Crystal data and experimental details 6 A. K.-Y. Jen, V. P. Rao, K. J. Drost, K. Y. Wong and M. P. Cava, are listed in Table 1; atomic coordinates and thermal param- J.Chem. Soc., Chem. Commun., 1994, 2057. 7 M. Guillemet, J. M. Raoul, F. Pelle�, A. Robert and eters, bond distances and angles have been deposited at the M. Baudy-Floc’h, J.Mater. Chem., 1995, 5, 35. Cambridge Crystallographic Data Centre (CCDC). See 8 C.-S. Kang, C. Heldmann, H.-J. Winkelhahn, M. Schulze, Information for Authors, J. Mater.Chem., 1998, Issue 1. Any D. Neher, G. Wegner, R. Wortmann, C. Glania and P. 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Gebhardt, Chem. Ber., 1964, 97, 1298. mined in chloroform solution with a WTW dipole meter 12 Reviews: (a) H.Prinzbach and E. Futterer, Adv. Heterocycl. Chem., coupled with an Abbe refractometer, in order to measure the 1966, 7, 39; (b) N. Lozac’h and M. Stavaux, Adv. Heterocycl. Chem., relative permittivity and the refractive index of the solutions. 1980, 27, 151. 13 J. P. Ferraris, T. O. Poehler, A. N. Bloch and D. O. Cowan, From these experimental data the dipole moment was deduced T etrahedron L ett., 1973, 2553.using the Guggenheim model.44 Static b(0) values were deduced 14 G. Steimecke, H. Sieler, R. Kirmse and E. Hoyer, Phosphorus from the experimental values using a two-level dispersion Sulfur Relat. Elem., 1979, 7, 49. model [eqn. (3)] 15 L. R. Melby, H. D. Hartzler and W. A. Sheppard, J. Org. Chem., 1974, 39, 3608.b(0)=b(l)[1-(2l0/2l)2][1-(l0/l)2] (3) 16 (a) W. Lehnert, T etrahedron L ett., 1970, 4723; (b) W. Lehnert, Synthesis, 1974, 667. (l being the fundamental wavelength and l0 the first maximum 17 T. Sugimoto, H. Awaji, I. Sugimoto, Y. Misaki, T. Kawase, absorption wavelength). S. Yoneda, Z. Yoshida, T. Kobayashi and H. Anzai, Chem. Mater., 1989, 1, 535. Computational details 18 A.J. Moore and M. R. Bryce, T etrahedron L ett., 1992, 33, 1373. 19 A. Aumu� ller and S. Hu� nig, Angew. Chem., Int. Ed. Engl., 1984, The calculations were performed using the GAUSSIAN 9445 23, 447. system of programs on IBM RS/6000 workstations and on a 20 B. J. Adger, C. Barrett, J. Brennan, M. A. McKervey and SGI Power Challenge L R8000 computer at the Department R. W. Murray, J.Chem. Soc., Chem. Commun., 1991, 1553. of Quý�mica Fý�sica of the University of Valencia. All the 21 B. J. Adger, C. Barrett, J. Brennan, P. McGuigan, M. A. McKervey calculations were carried out at the DFT level using the hybrid and B. Tarbit, J. Chem. Soc., Chem. Commun., 1993, 1220. 22 B. Golding, G. Kennedy and W. P. Watson, T etrahedron L ett., gradient-corrected B3P86 density functional46 and the 6-31G* 1988, 29, 5991.basis set,47 which includes polarisation d functions on sulfur, 23 N. C. Gonella and M. P. Cava, J. Org. Chem., 1979, 44, 930. nitrogen and carbon atoms. The Berny analytical gradient 24 (a) Z. Yoshida, T. Kawase, H. Awaji, I. Sugimoto, T. Sugimoto and method48 was used in all the geometry optimisations. The S. Yoneda, T etrahedron L ett., 1983, 24, 3469; (b) Z.Yoshida, requested convergence on the density matrix was 10-8 and the H. Awaji and T. Sugimoto, T etrahedron L ett., 1984, 25, 4227; threshold values for the maximum force and the maximum (c) T. K. Hansen, M. V. Lakshmikantham, M. P. Cava, R. M. displacement were 0.00045 and 0.0018 atomic units, respect- Metzger and J. Becher, J. Org. Chem., 1991, 56, 2720; (d) A. J.Moore, M. R. Bryce, D. J. Ando and M. B. Hursthouse, J. Chem. ively. All the molecules were restricted to be planar during Soc., Chem. Commun., 1991, 329; (e) T. K. Hansen, M. V. geometry optimisation. Lakshmikantham, M. P. Cava and J. Becher, J. Chem. Soc., Perkin T rans. 1, 1991, 2873; ( f ) M. R. Bryce, M. A. CoYn and W. Clegg, We thank the EPSRC and Great Lakes Chemicals (Europe) J.Org. Chem., 1992, 57, 1696; (g) D. Lorcy, R. Carlier, A. Robert, for funding the work in Durham and Belfast. The work in A. Tallec, P. Le Magueres and L. Ouahab, J. Org. Chem., 1995, 60, Valencia was supported by the CICYT Grant PB95-0428-C02- 2443; (h) Y. Misaki, T. Ohta, N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and S. Tanaka, J. Mater. Chem., 1995, 5, 1571; 02.We are grateful to the Leverhulme Trust for a scholarship (i) Review; M. R. Bryce, J. Mater. Chem., 1995, 5, 1481; ( j ) M. R. (to A.S.B.) and the Royal Society for Leverhulme Senior Bryce, A. J. Moore, B. K. Tanner, R. Whitehead, W. Clegg, Research Fellowship (to J.A.K.H.). F. Gerson and A. Lamprecht, Chem. Mater., 1996, 8, 1182; (k)T.-T. Nguyen, Y. Gouriou, M.Salle�, P. Fre` re, M. Jubault, A. Gorgues, L. Youpet and A. Riou, Bull. Soc. Chim. Fr., 1996, 133, 301. References 25 (a) M. R. Bryce, A. J. Moore, M. Hasan, G. J. Ashwell, A. T. Fraser, W. Clegg, M. B. Hursthouse and A. I. Karaulov, Angew. Chem., 1 Reviews: (a) Nonlinear Optical Properties of Organic Molec0, 29, 1450; (b) J. Dong, K. Yakushi and Crystals, ed.D. S. Chemla and J. Zyss, Academic Press, Boston, Y. Yamashita, J.Mater. Chem., 1995, 5, 1735. 1987; (b) P. N. Prasad and D. J. Williams, Introduction to Nonlinear 26 (a) U. Scho� berl, J. Salbeck and J. Daub, Adv. Mater., 1992, 4, 41; Optical EVects in Molecules and Polymers, Wiley, New York, 1991; (b) T. K. Hansen, M. V. Lakshmikantham, M. P. Cava, R. E. (c) Molecular Nonlinear Optics: Materials, Physics and Devices, ed.J. Zyss, Academic Press, Boston, 1994; (d) R. G. Denning, J.Mater. Niziurski-Mann, F. Jensen and J. Becher, J. Am. Chem. Soc., 1992, J. Mater. Chem., 1998, 8(5), 1173–1184 1183114, 5035; (c) A. S. Benahmed-Gasmi, P. Fre` re, B. Garrigues, 37 (a) A. Gavezzotti, J. Am. Chem. Soc., 1983, 105, 5220; (b) G. Filippini and A. Gavezzotti, Acta Crystallogr., Sect.B, 1993, A. Gorgues, M. Jubault, R. Carlier and F. Texier, T etrahedron 49, 868. L ett., 1992, 33, 6457; (d) A. Benahmed-Gasmi, P. Fre` re, 38 J. L. Oudar, J. Chem. Phys., 1977, 67, 446. E. H. Elandaloussi, J. Roncali, J. Orduna, J. Garý�n, M. Jubault, 39 S. Brasselet and J. Zyss, Int. J. Nonlinear Opt. Phys., 1996, 5, 671. A. Riou and A. Gorgues, Chem.Mater., 1996, 8, 2291. 40 (a) R. G. Parr and W. Yang, Density-Functional T heory of Atoms 27 S. Kugimiya, T. Lazarak, M. Blanchard-Desce and J.-M. Lehn, and Molecules, Oxford University Press, New York, 1989; J. Chem. Soc., Chem. Commun., 1991, 1179. (b) M. Levy, Proc. Natl. Acad. Sci. USA, 1979, 76, 6062; 28 Compound 11d was prepared by modification of the literature (c) T.Ziegler, Chem. Rev., 1991, 91, 651; (d) R. O. Jones and preparation for compound 11b, ref. 18, using tributylphosphine O. Gunnarsson, Rev. Mod. Phys., 1990, 61, 689. instead of triphenylphosphine. 41 (a) J. Andzelm, C. Sosa and R. A. Eades, J. Phys. Chem., 1993, 97, 29 (a) P. Fre` re, A. Belyasmine, A. Gorgues, G. Duguay, K. Boubekeur 4664; (b) C. W. Bauschlicher Jr., Chem. Phys. L ett., 1995, 246, 40; and P.Batail, T etrahedron L ett., 1993, 34, 4519; (b) P. Fre`re, (c) G. Rauhut and P. Pulay, J. Phys. Chem., 1995; 99, 3093; (d) J. S. A. Belyasmine, Y. Gouriou, M. Jubault, A. Gorgues, G. Duguay, Kwiatkowski and J. Leszczynski, J. Phys. Chem., 1996, 100, 941; S. Wood, C. D. Reynolds and M. R. Bryce, Bull. Soc. Chim. Fr., (e) J. A. C. Scheiner, J. Baker and J. W. Andzelm, J. Comput. Chem., 1995, 132, 975; (c) M. R. Bryce, M. Chalton, A. S. Batsanov, C. W. 1997, 18, 775; ( f ) V. Barone, C. Adamo and F. Mele, Chem. Phys. Lehmann and J. A. K. Howard, J. Chem. Soc., Perkin T rans. 2, L ett., 1996, 246, 290. 1996, 2367; (d) P. Leriche, A. Belyasmine, M. Salle�, P. Fre` re, 42 G. M. Sheldrick, SHELXTL, Version 5, Siemens Analytical X-Ray A. Gorgues, A. Riou, M. Jubault, J. Orduna and J. Garý�n, Instruments Inc., Madison, USA, 1995. T etrahedron L ett., 1996, 37, 8861. 43 TEXSAN: Single Crystal Structure Analysis Software, Version 5.0, 30 (a) Y. Mollier, F. Terrier and N. Lozach, Bull. Soc. Chim. Fr., 1964, Molecular Structure Corporation, TX, USA, 1989. 1778; (b) R. Pinel and Y. Mollier, Bull. Soc. Chim. Fr., 1972, 1385; 44 E. A. Guggenheim, T rans. Faraday Soc., 1949, 45, 203. (c) R. Pinel, Y. Mollier, J. P. de Barbeyarac and G. Pfister- 45 M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Guillouzo, C. R. Seances Acad. Sci., Ser. C, 1972, 275, 909; Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, (d) R. Pinel, Y. Mollier, E. C. Liaguno and I. C. Paul, J. Chem. J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Soc., Chem. Commun., 1971, 1352. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. 31 (a) S. Bezzi, M. 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B, 1972, 28, 214. local and gradient-corrected exchange and correlation terms, with 34 S. R. Marder, J. W. Perry, B. G. Tieman, C. B. Gorman, the nonlocal correlation provided by the ‘Perdew 86’ 46b S. Gilmour, S. L. Biddle and G. Bourhill, J. Am. Chem. Soc., 1993, expression. (a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648; 115, 2524. (b) J. P. Perdew, Phys. Rev. B, 1986, 33, 8822. 35 N.-H. Dung and J. Etienne, Acta Crystallogr., Sect. B, 1978, 34, 47 P. C. Hariharan and J. A. Pople, Chem. Phys. L ett., 1972, 16, 217. 48 H. B. Schlegel, J. Comput. Chem., 1982, 3, 214. 683. 36 H. Hopf, M. Kreutzer and P. G. Jones, Angew. Chem., Int. Ed. Engl., 1991, 30, 1127. Paper 7/08078F; Received 10th November, 1997 1184 J. Mater. Chem., 1998, 8(5), 1173&

ISSN:0959-9428    

DOI:10.1039/a708078f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Functionalized polyolefinic nonlinear optic chromophores incorporating the 1,3-dithiol-2-ylidene moiety as the electrondonating part T. T. Nguyen,a M. Salle�,*a† J. Delaunay,a A. Riou,a P. Richomme,a J. M. Raimundo,a A. Gorgues,*a I. Ledoux,b C. Dhenaut,b J. Zyss,b J. Ordunac and J. Garý�nc aL aboratoire Inge�nierie Mole�culaire et Mate�riaux Organiques, UMR CNRS 6501, Universite� d’Angers, 2 Bd L avoisier, F-49045 Angers, France bCentre National d’Etudes des T e�le�communications, France T e�le�com, 196 Av Henri Ravera, F-92220 Bagneux, France cDepartamento de Quý�mica Orga�nica, ICMA, Universidad de Zaragoza, CSIC, E-50009 Zaragoza, Spain The synthesis of a series of push-pull systems [donor (D)–acceptor (A)], associating the 1,3-dithiol-2-ylidene moiety (D) to various (A) fragments through polyolefinic linkages of various lengths, is described.Design optimization of these NLO phores is via systematic determination of the molecular first hyperpolarizabilities b by the EFISH method. Selected compounds of this series, displaying the highest b values, are then chemically functionalized in order to promote their covalent grafting to polymeric backbones.The quest for new chromophores possessing large molecular second-order nonlinearity is of current interest because of their potential applications in electro-optic devices. In this context, the design and synthesis of new D–p–A systems, where the electron-donor (D) and electron-acceptor (A) groups are separated by a p-conjugated linker, are presently a major focus.Moreover, a growing eVort is devoted to the preparation of polymers covalently functionalized with such chromophores, in order to produce long-term stable nonlinear optical (NLO) systems.1 The 1,3-dithiol-2-ylidene moiety is well known for its electron- donating properties, and has been extensively used as such, notably in the synthesis of p-donating molecules of the tetrathiafulvalene family.2 This donating ability has also been explored in the design of NLO chromophores.3 Nevertheless, very few examples of push-pull chromophores possessing the 1,3-dithiol-2-ylidene moiety have been designed to further incorporate main-chain or side-chain polymers.In this paper, we report on the synthesis of new push-pull conjugated polyenic systems incorporating the 1,3-dithiol-2- ylidene fragment as the donor part and various acceptor moities.A careful structural optimization of this class of S S NO2 S NO2 CO2Et CO2Et CO2Et CHO CN CN CN R1 R2 R1 = R2 = Me R1–R2 = (CH=CH)2 R1–R2 = SCH2CH2S a b c A n 4a–c n = 2, A = 5a,b n = 2, A = n = 1, A = n = 2, A = n = 3, A = n = 1, A = n = 1, A = 6a,b 7a,b 8a,b 9a,b 10a,b chromophores has been carried out in order to reach high second-order hyperpolarizabilities as well as to introduce BuLi furnished chromophores 4 bearing the 4-nitrophenyl functionalities which could favour their subsequent incorpor- substituent as the acceptor part (only the E-configuration is ation into polymeric backbones.observed for the double-bond formed during the olefination step).On the other hand, compounds 5–8 were obtained via Wittig–Horner olefinations of 1 and 2 with a phosphonate Synthesis anion generated under basic conditions from the corresponding The access to chromophores 4–10 involves key precursors 2 phosphonate esters. and 3, whose syntheses were performed via adaptation of the All of these compounds were fully characterized using diVerpreviously described procedures.4 Taking advantage of the ent spectroscopic methods, a careful NMR study (1H NMR, great synthetic potential of the aldehyde functionality in 2 and 13C NMR, COSY, HMQC, HMBC) being often needed to 3, we prepared target compounds 4–10 either through Wittig fully assign the molecular structures of compounds 4–8.(–Horner) type olefinations or Knoevenagel condensations Whereas 4 and 5 were obtained as mixtures of Z and E (Scheme 1).isomers, the trans configuration of the double bond formed in Treatment of aldehydes 2 with the commercially available the synthesis of compounds 6–8 was fully ascertained by NMR 4-nitrobenzyl(triphenyl)phosphonium bromide in presence of studies, as well as the s-trans conformation adopted by 8a in [2H6]DMSO, assigned via an NOE experiment.Furthermore, methanol recrystallization of 8a produced † E-mail: marc.salle@univ-angers.fr J. Mater. Chem., 1998, 8(5), 1185–1192 1185O S S 123 R1 R2 4a–c m = 0 m = 1 m = 2 (57–71%) 5a,b (56–60%) 6a,b (53–60%) 7a,b (52–63%) 8a,b (28–33%) R1 = R2 = Me R1–R2 = (CH=CH)2 R1–R2 = SCH2CH2S a (78–85%) (69–81%) 9a,b 10a,b b c i ii vi iii iv v m Scheme 1 Reagents and conditions: i, 4-nitrobenzyl(triphenyl)phosphonium bromide, BuLi, THF, reflux; ii, dimethyl (5-nitro-2-thienyl)- methylphosphonate, BuLi, THF, reflux; iii, triethyl phosphonoacetate, BuLi, THF, 0 °C; iv, CH2(CN)2, Et3N, dioxane, 0 °C; v, NCCH2CHO, MeONa, THF, room temp.; vi, triethyl 4-phosphonocrotonate, BuLi, THF, 0 °C CN CN NC NC S S S CN CN NC NC CN CN S S S S CH2-P(O)(OMe)2 S S S NH 11 + 2a + (81%) 11 12 (84%) ii [2+4] i Scheme 2 Reagents and conditions: i, Bu t OK, THF, room temp.; ii, DMF, room temp.contribution from the charge-separated resonance form to the ground-state structure. In our quest to synthesize new push-pull systems, we also attempted to graft the 2-(tricyanovinyl )thiophene fragment as the acceptor (A) group.For this purpose, we first synthesized the unsubstituted 2-thienyl derivative 11 through a Wittig– Horner olefination of 2a with diethyl (2-thienyl)methylphosphonate (Scheme 2). Unfortunately this compound, when treated with tetracyanoethylene in DMF, did not give the required addition of the tricyanovinyl group to the terminal position of 2a, but to compound 12 thanks to a [4+2] cycloaddition of tetracyanoethylene to the central polyolefinic linkage, followed either by a [2+2] process or an intramolecular nucleophilic addition, with prototropy.This unexpected structure was confirmed via an X-ray structural determination using a single crystal of 12 (Fig. 2).8 Alternatively, new push-pull systems 9 and 10 were prepared using Knoevenagel type condensations between aldehydes 2 and either malononitrile or cyanoacetaldehyde.Fig. 1 ORTEP view of compound 8a crystals suitable for a X-ray structural determination5 (Fig. 1). The most noticeable features of this structure lie in the occurrence of a perfectly planar s-trans structure, with relatively low Dr values between single and double bond lengths (average rCNC=1.372 A ° ; average rCMC=1.454; Dr=0.08 A °), corresponding to an optimized bond alternation for enhancement of quadratic and cubic NLO properties.6 This Dr value has to be compared with the one encountered in the case of an unsubstituted polyene such as octa-1,3,5,7-tetraene, which displays a Dr value of 0.11 A ° (average rCNC=1.340 A ° ; average rCMC=1.445 A ° ).7 This comparison provides direct evidence for Fig. 2 ORTEP view of compound 12 a low bond-length alternation in 8a, associated to an important 1186 J. Mater. Chem., 1998, 8(5), 1185–1192selected among structures 4–10 as the best candidates to be NLO properties structurally modified due to easy chemical accessibility and The second-order hyperpolarizabilities b of chromophores 1–5, good hyperpolarizability values. 9 and 10 were determined using an the electric field induced Prior to the target NLO active monomers 14 and 23, we second harmonic (EFISH) generation experiment9 using a needed to synthesize mono- and bis-(2-hydroxyethylsulfanyl) laser source operating at 1.34 mm, the compounds being dis- derivatives 13 and 22. solved in chloroform (Table 1). The relevant parameter for In the case of 13, we took advantage of the specific ability electro-optic applications is mb, where m is the ground state of the ethane-1,2-diyldisulfanyl group to undergo a ring opendipole moment. Static mb(0) values are calculated from exper- ing under basic conditions11 (essive imental mb (1.34 mm) ones using a two-level dispersion model treatment of compound 4c with an excess of Bu4NF and for b.9 bromoethanol allowed the formation of the hydroxy intermedi- All of the NLO-phores studied present large mb and mb(0) ate 13 as a mixture of Z and E isomers, the hydroxyethyl and values.As expected for donor–acceptor substituted polyenes, vinyl groups being disposed in a random fashion with respect extension of the conjugation length from 1a to 3a results in a to the polyene part.Subsequent esterification of 13 with significant enhancement of the second-order nonlinearity methacryloyl chloride finally aVorded the required 14. [mb(0) values: 2a/1a=9.0, 3a/2a=1.3]. On the other hand, the two-fold introduction of the meth- Compounds 3a, 4a, 10a and 9a on the one hand, and 3b, acrylate moiety first involved the preparation of the 1,3- 4b, 10b and 9b on the other hand essentially display the same dithiolium salt 19a (scheme 4).This synthesis was achieved in qualitative increase of mb(0) values when increasing the acceptor character of the end group for both series, with confirmation of the superiority of the dicyanovinyl moiety over the aldehyde group, the mb(0) values being increased by a factor of 2.6 and 2.3 for the a and b series, respectively.Additionally, the introduction of the nitrothienyl substituent in compound 5b results in a strong increase of the nonlinearity when compared to 4b, which confirms the utility of this electron-attracting substituent in the designing of new D–p–A NLO-phores. Investigation of the donor part was limited to the study of the influence of the R groups at the 4,5-positions of the 1,3- dithiol-2-ylidene electron donating moiety.Of course, varying the R groups leads to smaller diVerences in mb(0) than in the preceding study on the acceptor part, where the whole A fragment was changed. The superiority of the methyl group as a donating substituent (3a, 4a, 9a, 10a) over the benzo-fused fragment (3b, 4b, 9b, 10b) was established in all cases, with as expected a very small increase in mb(0) [mb(0) values: 3a/3b= 1.02, 4a/4b=1.18, 9a/9b=1.18, 10a/10b=1.01].Moreover, the 4,5-(ethane-1,2-diyldisulfanyl) substituted derivative 4c displays a mb(0) value between those of 4a and 4b, as expected from previous studies of its electron-donating behavior.3b Synthesis of polymer precursors In order to obtain long-term stable nonlinear systems, these chromophores have been functionalized to allow further polymerization and to reach side-chain polymers bearing pendant active NLO moieties.This was achieved by introducing methyl methacrylate fragments10 on the donor extremity of the push- S S S S S S S S HO S S S S O C O -14 4c (77%) (84%) iii -13 ( E / Z ) ( E / Z ) i,ii NO2 NO2 NO2 pull system. Scheme 3 Reagents and conditions: i, Bu4 NF, THF, room temp.; ii, Addition of the methyl methacrylate fragment was carried BrCH2CH2OH (1.1 equiv.), THF, room temp.; iii, methacryloyl chloride, pyridine, THF, reflux out at the periphery of chromophores of type 4, which were Table 1 Experimental data: lmax, ground state dipole moment m, mb measured at 1.34 mm and static mb(0) values deduced from experimental mb ones using a two-level dispersion model for b compound lmax(CH2Cl2)/nma m/D mb/10-48 esu mb(0)/10-48 esu 1a 397 (4.26) 6.9 25 16 2a 432 (4.43) 8.2 273 144 3a 463 (4.24) 8.4 436 193 3b 431 (4.36) 6.1 369 189 4a 499 (4.50) 8.1 1130 464 4b 465 (4.40) 8.0 860 392 4c 479 (4.05) 8.6 981 403 5b 521 (4.27) 8.1 2540 850 9a 541 (4.37) 9.4 1870 508 9b 502 (4.81) 7.9 1200 431 10a 550 (4.56) 9.2 1590 401 10b 507 (4.44) 8.2 1147 397 aValues in parentheses are log e.J. Mater. Chem., 1998, 8(5), 1185–1192 1187several steps from thioxo derivative 15,12 whose hydroxy functionalities are first reacted with benzoyl chloride to produce 16a. This compound could be further S-methylated with methyl trifluoromethanesulfonate to aVord 17a; no reaction was observed when using methyl iodide or dimethyl sulfate as alkylating agents.Reduction of the latter with sodium borohydride and subsequent treatment with hexafluorophosphoric acid furnished the required dithiolium intermediate 19a. Formation of the corresponding phosphonate ester by addition of trimethyl phosphite was followed by Wittig–Horner olefination with fumaraldehyde mono(diethyl acetal ).Further hydrolysis led to aldehyde 20a, which was converted to the push-pull system 21 thanks to a Wittig olefination with 4-nitrobenzyl(triphenyl) phosphonium bromide. Deprotection of the alcohol functionalities and two-fold esterification of 22 with methacryloyl chloride aVorded the expected polymer precursor 23. Attempts to copolymerise monomers 14 or 23 with methyl methacrylate in the presence of AIBN all resulted in chemical evolution of the NLO active part, as evidenced by extinction of the absorption bands related to the individual chromophores in the electronic spectra.This observation strongly suggests a lack of stability of the conjugated backbone under these polymerisation conditions. Alternatively, we attempted to prepare polyesters, containing the same optimized optically active group, by polycondensation between diol 22 and terephthaloyl chloride.Using various experimental conditions, we have been unable to isolate the target polymer, finding only short oligomers beside the [2+2] cyclocondensation product (m/z 1142). The introduction of these chromophores into other classes of polymers, notably polyimides, is underway.Conclusion We have synthesized a wide range of D–p–A systems incorporating 4,5-disubstituted 1,3-dithiol-2-ylidene moieties as the D part. EFISH measurements have shown these NLO phores to possess high second order nonlinearities, and have allowed us to evaluate the eVect of (i) the length of the p-conjugating spacer and (ii) the nature of the electron-withdrawing and electron-releasing substituents on the mb(0) values.Chemical modifications on one model chromophore allowed us to intro- S S S O Bz SMe TfO– S S S O H SMe S S S O Bz H S S S O Bz O S S R2S R2S S S S O Bz S S S S NO2 S S S S Bz 21 16a R1 = CH2CH2OBz (87%) b R1 = CH3 (78%) PF6 – + + 17a (96%) b (94%) 18a (94%) b 19a (67%) b (66%) 20a (78%) b (65%) R2 = CH2CH2OBz (65%) 22 R2 = CH2CH2OH (79%) 23 R2 = CH2CH2OCOCMe=CH2 (58%) R1S R1S R1S R1S R1S 20a 24 R2 = CH2CH2OBz (51%) 25 R2 = CH2CH2OH (60%) 20b 15 R1 = CH2CH2OH , 15' R1 = Me R1S HO NO2 x xi MeS R2S i ii iii iv v–viii ix xii duce polymerizable fragment(s) at the periphery of the D–p–A Scheme 4 Reagents and conditions: i, BzCl, pyridine, THF, room temp.; system.Considering the very attractive mb(0) value obtained ii, TfOMe, CH2Cl2, room temp.; iii, NaBH4, Pr i OH, MeCN, 0 °C; iv, with compound 5b possessing a nitrothienyl group as the HPF6, Ac2 O, 0 °C; v, NaI, P(OMe)3, MeCN, room temp.; vi, BuLi, acceptor part, chemical modification of this chromophore to -80 °C; vii, fumaraldehyde mono(dimethyl acetal ), THF, -80 °C�room temp.; viii, Amberlyst-15, H2O–acetone; ix, 4-nitro- hydroxy derivative 25 has been performed according to a benzyl(triphenyl )phosphonium bromide, BuLi, THF, reflux; x, KOH, similar synthetic strategy as for compound 22 (Scheme 4).THF–MeOH–H2O (105551), reflux; xi, methacryloyl chloride, pyri- Attempts to covalently graft this chromophore onto poly(imdine, THF, reflux; xii, dimethyl (5-nitro-2-thienyl )methylphosphonate, ide-co-siloxanes) are in progress.BuLi, THF, reflux; xiii, KOH, THF–MeOH–H2O (105551), reflux Syntheses of 4a–c Experimental 4-Nitrobenzyl(triphenyl)phosphonium bromide (2.2 mmol) Melting points were obtained using a Rechert-Jung hot-stage was dissolved in dried THF (10 ml ), and BunLi (1.6 M in microscope apparatus and are uncorrected. IR spectra were hexane; 2.2 mmol) was added at room temperature.The mixrecorded on a Perkin-Elmer model 841 spectrophotometer, ture was stirred for 15 min and aldehyde 2 (2 mmol) was added samples being embedded in KBr discs or Fluorolube mulls. dropwise. The reaction mixture was refluxed for 2 h. After 1H and 13C NMR spectra were recorded on a JEOL cooli, the solvents were removed under reduced pressure GSX270WB spectrometer operating respectively at 270 and and the residue was dissolved in CH2Cl2, washed with water 67.5 MHz or on a Bruker Avance DRX500 operating at 500 and dried (MgSO4). The crude material obtained after evaporand 125.7 MHz, respectively; d values are given in ppm (relative ation of CH2Cl2 was chromatographed over silica gel (CH2Cl2 to TMS) and coupling constants (J) in Hz.Mass spectra were as eluent) to produce 4a–c as brown powders. recorded in EI or FAB mode on a VG Autospec. UV–VIS spectra were recorded on a Perkin-Elmer Lambda 2 spec- 5-(4,5-Dimethyl-1,3-dithiol-2-ylidene)-1-(4- trometer. Elemental analyses were performed by the Service nitrophenyl )penta-1,3-diene 4a. Yield 71%, mp 173–174 °C; 1H central d’analyses du CNRS (Vernaison, France).Column NMR (CDCl3) 8.14 (d, 2H, 3J=8.5 Hz), 7.66 (d, 2H, 3J= chromatography separations and purifications were carried 8.7 Hz), 7.29 (dd, 1H, 3J=10.5, 15.5 Hz), 6.63 (d, 1H, 3J= 15.5 Hz), 6.38–6.20 (m, 3H), 1.94 (s, 6H); 13C NMR (CDCl3) out on Merck silica gel 60 (0.040–0.0063 nm). 1188 J. Mater. Chem., 1998, 8(5), 1185–1192145.4, 144.1, 139.5, 133.9, 132.7, 126.8, 125.9, 125.6, 123.7, 121.6, Ethyl 4-(4,5-dimethyl-1,3-dithiol-2-ylidene)but-2-enoate 6a.Yield 60%; 1H NMR (CDCl3) 7.37 (dd, 1H, 3J=11.8, 14.8 Hz), 110.9, 13.1, 12.8 (Calc. for C16H15NO2S2: C, 58.53; H, 4.06. Found: C, 58.10; H, 4.17%); m/z (EI) (%) 317 (M+, 100), 195 6,10 (d, 1H, 3J=11.75 Hz), 5.54 (d, 1H, 3J=14.8 Hz), 4.22 (q, 2H), 1.96 (s, 3H), 1.93 (s, 3H), 1.30 (t, 3H); m/z (EI) (%) 242 (18), 131 (22), 59 (18); nmax(KBr)/cm-1 1504, 1336 (NO2).(M+, 87), 197 (100), 170 (74), 116 (53), 71 (48), 59 (20). 5-(1,3-Benzodithiol-2-ylidene)-1-(4-nitrophenyl )penta-1,3- diene 4b. Yield 57%, mp 246–248 °C; 1H NMR (CDCl3) 8.16 Ethyl 4-(1,3-Benzodithiol-2-ylidene)but-2-enoate 6b. Yield (d, 2H, 3J=8.7 Hz), 7.49 (d, 2H, 3J=8.7 Hz), 7.20 (m, 4H), 7.03 53%, mp 80–82 °C; 1H NMR (CDCl3) 7.34 (dd, 1H, 3J=11.5, (dd, 1H, 3J=11.0, 15.5 Hz), 6.54 (d, 1H, 3J=15.5 Hz), 6.42 (dd, 14.8 Hz,), 7.22 (m, 4 H), 6.24 (d, 1H, 3J=11.5 Hz), 5.65 (d, 1H, 1H, 3J=11.3, 13.8 Hz), 6.26 (dd, 1H, 3J=11.0, 13.8 Hz), 6.22 3J=14.8Hz), 4.22 (q, 2H), 1.30 (t, 3H); 13C NMR (CDCl3) (d, 1H, 3J=11.3 Hz); 13C NMR (CDCl3) 151.5, 135.7, 133.9, 167.0, 145.6, 139.3, 135.2, 134.7, 125.7, 125.6, 121.4, 121.2, 115.4, 132.5, 128.2, 126.2, 126.0, 125.8, 125.5, 124.2, 121.7, 121.5, 114.1 110.9, 59.7, 13.9; m/z (EI) (%) 264 (M+, 98), 236 (8), 219 (70), (Calc.for C18H13NO2S2: C, 63.71; H, 3.83; N, 4.13; O, 9.44; S, 192 (100), 147 (28), 69 (12); nmax(KBr)/cm-1 1696 (CO). 18.88. Found: C, 63.83; H, 4.03; N, 4.23; O, 9.91; S, 18.58%); m/z (EI) (%) 339 (M+, 100), 292 (29), 153 (26), 140 (30), 77 Ethyl 6-(4,5-Dimethyl-1,3-dithiol-2-ylidene)hexa-2,4-dieno- (7); nmax(KBr)/cm-1 1565, 1335 (NO2).ate 7a. Yield 52%, mp 120–123 °C; 1H NMR (CDCl3) 7.31 (dd, 1H, 3J=11.5, 15.0 Hz), 6.43 (dd, 1H, 3J=11.5, 14.6 Hz), 5-[4,5-(Ethane-1,2-diyldisulfanyl)-1,3-dithiol-2-ylidene]-1- 6,06 (d, 1H, 3J=11.5 Hz), 6.03 (dd, 1H, 3J=11.5, 14.6 Hz), (4-nitrophenyl )penta-1,3-diene 4c.Yield 60%, mp 220–221 °C; 5.76(d, 1H, 3J=15.0 Hz), 4.17 (q, 2H), 1.96, (s, 3H), 1.93 (s, 1H NMR (CDCl3) 8.17 (d, 2H, 3J=8.9 Hz), 7.47 (d, 2H, 3J= 3H), 1.28 (t, 3H); 13C NMR (CDCl3) 168.0, 145.6, 143.7, 137.5, 8.9 Hz), 6.98 (dd, 1H, 3J=10.1, 15.5 Hz), 6.53 (d, 1H, 3J= 124.3, 122.7, 122.9, 118.2, 111.1, 60.5, 14.8, 14.0, 13.7; m/z (EI) 15.5 Hz), 6.41 (dd, 1H, 3J=10.3, 13.8 Hz), 6.23 (dd, 1H, 3J= (%) 268 (M+, 41), 223 (8), 195 (100), 59 (8); nmax(KBr)/cm-1 10.1, 13.8 Hz), 6.22 (d, 1H, 3J=10.3Hz), 3.33 (s, 4H); 13C NMR 1697 (CO).(CDCl3) 146.2, 144.2, 135.1, 133.8, 132.2, 128.7, 128.4, 127.5, 126.3, 124.2, 114.3, 29.7, 29.6 (Calc. for C16H13NO2S4: C, 50.66; Ethyl 6-(1,3-Benzodithiol-2-ylidene)hexa-2,4-dienoate 7b. H, 3.43; N, 3.69. Found: C, 50.46; H, 3.53; N, 3.49%); m/z (EI) Yield 63%, mp 103 °C; 1H NMR (CDCl3) 7.34 (dd, 1H, 3J= (%) 379 (M+, 100), 184 (92), 152 (34), 88 (35); nmax(KBr)/cm-1 11.5, 15 Hz), 7.19 (m, 4 H), 6.53 (dd, 1H, 3J=11.3, 14.3 Hz), 1526, 1332 (NO2). 6.21 (d, 1H, 3J=11.3 Hz), 6.13 (dd, 1H, 3J=11.5, 14.3 Hz), 5.83 (d, 1H, 3J=15 Hz), 4.20 (q, 2H), 1.29 (t, 3H); 13C NMR Syntheses of 5a,b (CDCl3) 167.3, 144.6, 140.4, 136.3, 135.7, 135.5, 126.1, 125.9, 121.8, 121.6, 125.8, 119.2, 113.4, 60.2, 14.3 (Calc. for Using a similar procedure as for 4a–c, aldehyde 2 was reacted C15H14O2S2: C, 62.02; H, 4.82; O, 11.03; S, 22.06.Found: C, with dimethyl (5-nitro-2-thienyl)methylphosphonate as 61.70; H, 4.90; O, 10.88; S, 21.63%); m/z (EI) (%) 290 (M+, Wittig–Horner reagent. 36), 245 (9), 217 (100), 184 (23), 69 (8); nmax(KBr)/cm-1 1711 (CO). 5-(4,5-Dimethyl-1,3-dithiol-2-ylidene)-1-(5-nitro-2- thienyl)penta-1,3-diene 5a. Yield 56%, black powder, mp Ethyl 8-(4,5-Dimethyl-1,3-dithiol-2-ylidene)octa-2,4-dienoate 179–180 °C; 1H NMR (CDCl3) 7.78 (d, 1H, 3J=4.2 Hz), 6.85 8a. Yield 33%, mp 135 °C; Chemical shifts of diVerent 1H and (dd, 1H, 3J=10.8, 15.3 Hz), 6.81 (d, 1H, 3J=4.0 Hz), 6.47 (d, 13C nuclei were assigned from COSY [1H,1H] and HMQC 1H, 3J=15.0 Hz), 6.35 (dd, 1H, 3J=11.3, 14.6 Hz), 6.09 (d, 1H, spectra.The all-trans configuration of the conjugated spacer 3J=11.5 Hz), 6.05 (dd, 1H, 3J=11.0, 14.6 Hz), 1.98 (s, 3H), was confirmed from NOE measurements and X-ray diVraction: 1.95 (s, 3H); 13C NMR (CDCl3) 151.9, 143.0, 141.8, 135.2, 1H NMR (CDCl3) 7.18 (dd, 1H, 3J=11.5, 15.2 Hz), 6.47 (dd, 134.2, 130.0, 125.3, 123.5, 122.5, 120.7, 111.3, 13.6, 13.2; m/z 1H, 3J=10.9, 14.7 Hz), 6.13 (m, 2H), 5.93 (d, 1H, 3J=11.9Hz), (EI) (%) 323 (M+, 100), 147 (67), 131 (26), 59 (24); 5.91 (dd, 1H, 3J=11.0, 16.2 Hz), 5.18 (d, 1H, 3J=15.2 Hz), 4.10 nmax(KBr)/cm-1 1520, 1317 (NO2).(q, 2H), 1.96 (s, 3H), 1.93 (s, 3H), 1.20 (t, 3H); 13C NMR (CDCl3) 166.4, 144.9, 141.9, 139.3, 133.6, 127.9, 126.7, 122.3, 5-(1,3-Benzodithiol-2-ylidene)-1-(5-nitro-2-thienyl )penta-1,3- 122.1, 118.6, 111.7, 59.6, 14.2, 13.3, 12.9 (Calc.for C15H18O2S2: diene 5b. Yield 60%, violet powder, mp 203–205 °C; 1H NMR C, 61.22; H, 6.12; O, 10.88; S, 21.76. Found: C, 61.29; H, 6.12; (CDCl3) 7.8 (d, 1H, 3J=4.2 Hz), 7.21 (m, 4H), 6.88 (dd, 1H, O, 10.89; S, 21.57%); m/z (EI) (%) 294 (M+, 35), 265 (10), 221 3J=10.6, 15.5 Hz), 6.85 (d, 1H, 3J=4.5 Hz), 6.54(d, 1H, 3J= (100), 157 (15), 91 (19); nmax(KBr)/cm-1 1702 (CO). 15.5 Hz), 6.44 (dd, 1H, 3J=11.3, 14.3 Hz), 6.23 (d, 1H, 3J= 11.3 Hz), 6.14 (dd, 1H, 3J=14.3 Hz); 13C NMR (CDCl3) 151.9, Ethyl 8-(1,3-Benzodithiol-2-ylidene)octa-2,4-dienoate 8b. 138.4, 135.3, 135.1, 134.1, 133, 129.5, 126.7, 125.7, 125.5, 121.5, Yield 28%, mp 135 °C; 1H NMR (CDCl3) 7.35 (m, 4H), 7.28 121.4, 123.5, 113.5 (Calc.for C16H11NO2S3: C, 55.63; H, 3.21; (dd, 1H, 3J=11.5, 15.0 Hz), 6.85 (dd, 1H, 3J=10.8, 14.6 Hz), N, 4.05; O, 9.26; S, 27.84. Found: C, 55.49; H, 3.13; N, 4.05; O, 6.50–6.21 (m, 4H), 5.93 (d, 1H, 3J=15.0 Hz), 4.11 (q, 2H), 1.21 9.57; S, 27.52%); m/z (EI) (%) 345 (M+, 100), 147 (77), 69 (t, 3H); 13C NMR (CDCl3) 166.3, 144.7, 141.5, 136.6, 134.8, (60); nmax(KBr)/cm-1 1526, 1324 (NO2). 133, 129, 128.6, 126.6, 126.4, 122.3, 122.2, 119.4, 114.6, 59.7, 14.3 (Calc. for C17H16O2S2: C, 64.55; H, 5.06; O, 10.12. Found: Syntheses of 6a,b, 7a,b and 8a,b C, 64.39; H, 5.03; O, 10.21%); m/z (EI) (%) 316 (M+, 35), 287 A solution of aldehyde 1 (1 mmol) and triethyl phosphonoacet- (11), 243 (100); nmax(KBr)/cm-1 1698 (CO).ate (1 mmol) (for 6a,b), aldehyde 2 (1 mmol) and triethyl phosphonoacetate (1 mmol) (for 7a,b) or aldehyde 2 (1 mmol) Syntheses of 9a,b with triethyl 4-phosphonocrotonate (1 mmol) (for 8a,b) in dried THF (10 ml ) was treated with BunLi (1.6 M in hexane, A mixture of aldehyde 2 (1 mmol), malononitrile (1.1 mmol) and triethylamine (1 ml) in dioxane (20 ml ) was stirred for 1.1 equiv.) at 0 °C.The reaction mixture was stirred for 2 h, the solvents were removed under reduced pressure and the 10 min at 0 °C. The reaction mixture was then diluted with CH2Cl2 (100 ml), washed with water and dried (MgSO4). The residue was dissolved in CH2Cl2, washed with water and dried (MgSO4). Evaporation of the solvent and silica gel chromatog- solvent was removed and the reaction product was purified by silica gel chromatography (CH2Cl2 as eluent) to produce 9a,b raphy (CH2Cl2 as eluent) produced 6a,b, 7a,b and 8a,b as yellow powders.as blue powders. J. Mater. Chem., 1998, 8(5), 1185–1192 11896-(4,5-Dimethyl-1,3-dithiol-2-ylidene)-2-cyanohexa-2,4- Synthesis of 12 dienenitrile 9a. Yield 78%, mp 227–232 °C; 1H NMR (CDCl3) Tetracyanoethylene (1.5 mmol) was added portionwise to a 7.33 (d, 1H, 3J=12.2 Hz), 6.88 (dd, 1H, 3J=12.0, 13.4 Hz), 6.46 solution of compound 11 (1 mmol) in DMF (10 ml ).The (dd, 1H, 3J=11.8, 13.4 Hz), 6.28 (d, 1H, 3J=11.8 Hz), 2.09 (s, homogeneous mixture was stirred for one day at room tempera- 6H); 13C NMR (CDCl3) 160.3, 159.1, 146.5, 126.3, 126.2, ture, and then diluted with CH2Cl2 (100 ml), washed with 118.9, 116.0, 114.0, 111.0, 74.4, 14.1, 13.7; m/z (EI) (%) 246 water and dried (MgSO4).Solvent was removed under reduced (M+, 100), 249 (12), 71 (22), 59 (22), 54 (35); nmax(KBr)/cm-1 pressure and the yellow solid residue was chromatographed 2211 (CN). over silica gel (CH2Cl2 as eluent). Crystals suitable for X-ray analysis were obtained from chloroform. 6-(1,3-Benzodithiol-2-ylidene)-2-cyanohexa-2,4-dienenitrile 9b.Yield 85%, mp 242 °C; 1H NMR (CDCl3) 7.42 (d, 1H, 3J= 1,8,8-Tricyano-2-(2-thienyl )-6-(4,5-dimethyl-1,3-dithiol-2- 12.7 Hz), 7.31 (m, 4H), 6.97 (dd, 1H, 3J=12.0, 13.9 Hz), 6.49 ylidene)-7-iminobicyclo[3.2.1]oct-3-ene 12. Yield 84%, yellow (dd, 1H, 3J=12.0, 13.9 Hz), 6.42 (d, 1H, 3Jab=12.0 Hz); 13C powder, mp 245 °C; 1H NMR (CDCl3) 9.08 (s, 1H), 7.31 (d, NMR (CDCl3) 159.4, 155.1, 144.9, 140.8, 135.8, 127.4, 122.7, 1H, 3J=4.9 Hz), 7.03 (d, 1H, 3J=3.7 Hz), 6.99 (m, 1H), 6.47 121.4, 114.8, 112.8 (Calc.for C14H8N2S2: C, 62.68; H, 2.98; N, (dd, 1H, 3J=6.5, 9.6 Hz), 5.90 (dd, 1H, 3J=2.8, 9.6 Hz), 4.61 10.44; S, 23.88. Found: C, 62.33; H, 3.00; N, 10.33; S, 23.97%); (t, 1H), 3.92 (d, 1H, 3J=6.5 Hz), 2.14 (s, 3H), 2.11 (s, 3H); m/z m/z (EI) (%) 268 (M+, 100), 242 (8), 152 (25), 108 (14), 69 (EI) (%) 406 (M+, 100), 297 (23), 160 (26), 233 (85), 208 (40), (11); nmax(KBr)/cm-1 2220, 2204 (CN). 131 (47); nmax(KBr)/cm-1 3267 (NH), 2247 (CN). Synthesis of 13 Syntheses of 10a,b To a solution of 4c (0.5 mmol) in THF (10 ml ) was added in A solution of aldehyde 2 (1 mmol), cyanoacetaldehyde diethyl one portion an excess (5 mmol) of Bu4NF (1 M solution in acetal (1 mmol) and sodium methoxide (2 mmol) in dried THF THF) at room temperature.The red solution was stirred for (10 ml ) was stirred at room temperature for three days (in the 15 min, the colour turning to violet, and 2-bromoethanol case of 10a) or one day (in the case of 10b). Instantaneous (0.55 mmol) was added.The reaction mixture was stirred for hydrolysis was carried out by adding 50 ml of THF and 50 ml 6 h. The THF was then evaporated and the residue was of HCl (2 M). The solution was diluted with CH2Cl2 and dissolved in CH2Cl2, washed with water and dried (MgSO4). successively washed with water, saturated NaHCO3 and brine. The CH2Cl2 was evaporated and the residue was chromato- The organic phase was dried, evaporated and the residue was graphed over silica gel (CH2Cl2 as eluent) to give 13 as a chromatographed on silica gel (CH2Cl2 as eluent) to give 10a,b brown powder (probably as a mixture of Z and E isomers as violet powders. which are spectroscopically indistinguishable). 6-(4,5-Dimethyl-1,3-dithiol-2-ylidene)-2-cyanohexa-2,4- 5-[4-Ethenylsulfanyl-5-(2-hydroxyethylsulfanyl)-1,3-dithioldienal 10a.Yield 69%, mp 231 °C; 1H NMR (CDCl3) 9.39 (s, 2-ylidene]-1-(4-nitrophenyl)penta-1,3-diene 13. Yield 77%; 1H 1H), 7.57 (d, 1H), 7.02 (dd, 1H), 6.48 (dd, 1H), 6.36 (d, 1H), NMR (CDCl3) 8.17 (d, 2H), 7.48 (d, 2H), 6.98 (dd, 1H, 3J= 2.11 (s, 3H), 2.09 (s, 3H); m/z (EI) (%) 249 (M+, 70), 220 9.8, 15.4 Hz), 6.55 (d, 1H, 3J=15.4 Hz), 6.40 (dd, 1H, 3J=9.4, (100), 170 (12), 144 (12), 116 (21), 71 (24), 59 (28); 15.6 Hz), 6.25 (m, 3H), 5.48 (m, 2H), 3.79 (m, 2H), 3.00, (t, nmax(KBr)/cm-1 2211 (CN), 1659 (CO). 2H), 2.17 (t, 1H); 13C NMR (CDCl3) 146.3, 144, 135.6, 133.6, 131.5, 128.9, 128.8, 128.7, 126.3, 126.1, 117.7, 117.6, 114.9, 60.2, 39.0 (Calc for C18H17NO3S4: C, 51.04; H, 4.04; N, 3.30; O, 6-(1,3-Benzodithiol-2-ylidene)-2-cyanohexa-2,4-dienal 10b. 11.33; S, 30.27. Found: C, 50.91; H, 4.02; N, 3.32; O, 11.04; S, Yield 81%, mp 218 °C; 1H NMR (CDCl3) 9.44 (s, 1H), 7.63 30.32%); m/z (EI) (%) 423 (M+, 100), 184 (84), 152 (43), 103 (d, 1H, 3J=12 Hz), 7.52 (m, 4 H), 7.09 (dd, 1H, 3J=12.0, (43), 71 (44), 59 (12); nmax(KBr)/cm-1 3337 (OH), 1524, 13.6 Hz), 6.63 (dd, 1H, 3J=12.0, 13.6 Hz), 6.49 (d, 1H, 3J= 1334 (NO2). 12Hz); 13C NMR (CDCl3) 185.7, 157.1, 153.6, 144.8, 134.9, 126.4, 126.3, 121.8, 121.4, 114.0, 112.5, 109.1, 76.1 (Calc. for Synthesis of 14 C14H9NOS2: C, 61.97; H, 3.34; O, 5.89. Found: C, 61.92; H, 3.25; O, 5.22%); m/z (EI) (%) 271 (M+, 85), 242 (100), 108 To a solution of 13 (0.5 mmol) and pyridine (0.1 ml) in dried (34), 69 (30); nmax(KBr)/cm-1 2216 (CN), 1681 (CO). THF (10 ml ) was added dropwise a solution of freshly distillated methacryloyl chloride (1 mmol) in dried THF (5 ml).The reaction mixture was refluxed for 3 h, THF was removed Synthesis of 11 under reduced pressure and the residue was dissolved in Potassium tert-butoxide (1.5 mmol) was slowly added at room CH2Cl2, washed with water and dried (MgSO4). After removtemperature to a solution of aldehyde 2a (1 mmol) and diethyl ing the solvent, the residue was chromatographed over silica (2-thienyl)methylphosphonate (1.5 mmol) in THF (10 ml ).The gel (CH2Cl2 as eluent) to give 14 as a brown powder. mixture was stirred for 30 min and diluted with CH2Cl2 5-[4-Ethenylsulfanyl-5-(2-methacryloyloxyethylsulfanyl)- (50 ml ), washed with water and dried (MgSO4). The solvent 1,3-dithiol-2-ylidene]-1-(4-nitrophenyl)penta-1,3-diene 14.Yield was evaporated and the solid product was recrystallized from 84%; 1H NMR (CDCl3) 8.17 (d, 2H), 7.49 (d, 2H), 6.99 (dd, methanol. 1H, 3J=9.9, 15.5 Hz), 6.54 (d, 1H, 3J=15.5 Hz), 6.36 (dd, 1H, 3J=9.4, 16.4 Hz), 6.20 (m, 4H), 5.62 (1H), 5.45 (2H), 4.37 (t, 5-(4,5-Dimethyl-1,3-dithiol-2-ylidene)-1-(2-thienyl )penta- 2H), 3.09 (m, 2H), 1.96 (s, 3H); m/z (EI) (%) 491 (M+, 14), 1,3-diene 11.Yield 81%, yellow powder; 1H NMR (CDCl3) 184 (19), 113 (100), 69 (67); nmax(KBr)/cm-1 1720 (CO), 1530, (chemical shifts of diVerent protons were assigned via a COSY 1335 (NO2). 45 1H,1H experiment) 7.12 (d, 1H, 3J=4.9 Hz), 6.94 (d, 1H, 3J=3.7 Hz), 6.91 (dd, 1H), 6.62 (m, 2H), 6.10 (m, 3H), 1.94 (s, Synthesis of 16a 3H), 1.91 (s, 3H); 13C NMR (CDCl3) 143.5, 136.2, 130.0, 129.5, 127.6, 127.0, 125.0, 123.7, 123.1, 121.7, 121.6, 111.9, 13.6, 13.25; To a solution of 1511 (10 mmol) and pyridine (3.2 ml, 40 mmol) in THF (20 ml ) was added dropwise benzoyl chloride m/z (EI) (%) 278 (M+, 100), 191 (20), 160 (26), 147 (48), 131 (42), 115 (33).(40 mmol) in dry THF (10 mL) at room temperature. After 1190 J.Mater. Chem., 1998, 8(5), 1185–1192stirring for 3 h, the THF was evaporated. The residue was 4,5-Bis(2-benzoyloxyethylsulfanyl)-1,3-dithiolium hexa- fluorophosphate 19a. Yield 67%, pinkish powder, mp 148 °C; dissolved in CH2Cl2, washed with water and dried over MgSO4. After removing the solvent, 16 was purified by chrom- 1H NMR (CDCl3) 8.20 (dd, 4H), 7.43 (m, 6H), 6.38 (s, 1H), 4.49 (t, 4H), 3.16 (t, 4H).atography over silica gel ( light petroleum–CH2Cl2 152 as eluent) and obtained as a yellow powder. 4-(2-Benzoyloxyethylsulfanyl)-5-methylsulfanyl-1,3- dithiolium hexafluorophosphate 19b. Yield 66%, violet powder, 4,5-Bis(2-benzoyloxyethylsulfanyl)-2-thioxo-1,3-dithiole 16a. mp 110 °C; m/z (DAB) (%) 329 (100, M-PF6). Yield 87%, mp 82–85 °C; 1H NMR (CDCl3) 8.10 (dd, 4H), 7.52 (m, 6H), 4.50 (t, 4H), 3.20 (t, 4H); m/z (EI) (%) 494 (M+, Synthesis of 20a,b 25), 149 (100), 105 (61), 77 (33).To a solution of 19a or 19b (1 mmol) in dry acetonitrile Synthesis of 16b (10 mL) were added successively potassium iodide (1 mmol) and trimethyl phosphite (1 mmol) at room temperature. The Using a similar procedure as for 16a, a solution of thione 15¾ mixture was stirred for 15 min, the solvent was evaporated (10 mmol) and pyridine (20 mmol) was reacted with benzoyl and the residue was immediately dissolved in dry THF (10 ml ).chloride (20 mmol) in dry THF. The phosphonate anion was generated from BunLi (=1.1 equiv., 1.6 M in hexane) at -80 °C. A stoichiometric amount 4-(2-Benzoyloxyethylsulfanyl)-5-methylsulfanyl-2-thioxoof fumaraldehyde mono(dimethyl acetal) in dry THF was then 1,3-dithiole 16b.Yield 78%, mp <50 °C; 1H NMR (CDCl3) added dropwise and the reaction was allowed to warm to 8.10 (dd, 2H), 7.50 (m, 3H), 4.57 (t, 2H), 3.23 (t, 2H), 2.43 (s, room temperature. THF was removed in vacuo, the residue 3H); m/z (EI) (%) 360 (M+, 40), 149 (100), 105 (65), 77 (35). was dissolved in CH2Cl2 and washed with water. The obtained acetal was hydrolyzed with Amberlyst-15 (0.4 g) in wet acetone. Synthesis of 17a,b The course of the reaction was monitored by TLC.After removing the solvent, the residue was purified by chromatogra- Methyl trifluoromethanesulfonate (15.3 mmol) was added phy over silica gel (CH2Cl2 as eluent) and 20a or 20b was dropwise to a solution of 16a,b (8.5 mmol) in dry CH2Cl2 obtained as a yellow oil.(30 ml ). The solution was stirred at room temperature for 4 h. After addition of diethyl ether (200 ml), a yellow precipitate 4-[4,5-Bis(2-benzoyloxyethylsulfanyl)-1,3-dithiol-2- was formed, filtered and rinsed with diethyl ether. ylidene]but-2-enal 20a. Yield 78%; 1H NMR (CDCl3) 9.49 (d, 1H, 3J=8 Hz), 8.02 (dd, 4H), 7.54, 7.41 (m, 6H), 6.87 (dd, 1H, 2-Methylsulfanyl-4,5-bis(2-benzoyloxyethylsulfanyl)-1,3- 3J=11.5, 14.5 Hz), 6.21 (d, 1H, 3J=11.5 Hz), 5.91 (dd, 1H, dithiolium trifluoromethanesulfonate 17a.Yield 96%, mp 3J=8.0, 14.5 Hz), 4.52 (t, 2H), 4.51 (t, 2H), 3.19 (t, 4H); 13C 102–103 °C; 1H NMR (CDCl3) 8.06 (dd, 4H), 7.46 (m, 6H), NMR (CDCl3) 192.9, 161.1, 148.6, 145.7, 133.3, 129.7, 128.4, 4.63 (t, 4H), 3.53 (t, 4H), 3.10 (s, 3H). 128.2, 126.6, 111.7, 63.4, 34.7; m/z (EI) (%) 530 (M+, 11), 149 (100), 105 (66), 77 (33); nmax(KBr)/cm-1 1718 (CO), 1667 (CO). 2,5-Dimethylsulfanyl-4-(2-benzoyloxyethylsulfanyl )-1,3- dithiolium trifluoromethanesulfonate 17b. Yield 94%, mp 4-[4-(2-Benzoyloxyethylsulfanyl)-5-methylsulfanyl-1,3- 92–93 °C; 1H NMR (CDCl3) 8.10 (dd, 2H), 7.50 (m, 3H), 4.60 dithiol-2-ylidene]but-2-enal 20b.Yield 65%; 1H NMR (CDCl3) (t, 2H), 3.50 (t, 2H), 3.16 (s, 3H), 2.76 (s, 3H). 9.50, 9.47 (2d, 1H, Z+E isomers), 8.02 (dd, 2H), 7.45 (m, 3H), 6.95 (m, 1H, 3J=11.5, 14.5 Hz), 6.25 (m, 1H, 3J=11.5 Hz), 5.93 Synthesis of 18a,b (m, 1H, 3J=8.0, 14.5 Hz), 4.55 (t, 2H), 3.20 (t, 2H), 2.42, 2.40 (2s, 3H); m/z (EI) (%) 396 (M+, 25), 149 (100), 105 (54), 77 (30).Compound 17a or 17b (8 mmol), dissolved in a minimal amount of acetonitrile, was added dropwise to a suspension Synthesis of 21 of sodium borohydride (8.8 mmol) in isopropyl alcohol (4 ml) cooled at 0 °C, the temperature of the reaction mixture being Using a similar procedure as for 4a–c, aldehyde 20a was maintained below 5 °C. The mixture was then stirred at room reacted with 4-nitrobenzyl(triphenyl)phosphonium bromide as temperature for h, extracted with diethyl ether, washed with the Wittig reagent.water and dried (MgSO4). The solvents were evaporated and the resulting pinkish oil was used without further purification 5-[4,5-Bis(2-benzoyloxyethylsulfanyl)-1,3-dithiol-2-ylidene]- for the next step. 1-(4-nitrophenyl )penta-1,3-diene 21. Yield 65%, brown powder, mp 95–99 °C; 1H NMR (CDCl3) 8.16 (d, 2H, 3J=8.9 Hz), 8.05 2-Methylsulfanyl-4,5-bis(2-benzoyloxyethylsulfanyl)-1,3- (m, 4H), 7.49 (m, 8H), 6.98 (dd, 1H, 3J=10.1, 15.5 Hz), 6.54 dithiole 18a.Yield 94%; 1H NMR (CDCl3) 8.10 (dd, 4H) 7.55 (d, 1H, 3J=15.5 Hz), 6.17 (m, 3H), 4.51 (t, 4H), 3.18 (t, 4H); (m, 6H), 5.83 (s, 1H), 4.53 (t, 4H), 3.20 (t, 4H), 2.30 (s, 3H). 13C NMR (CDCl3) 166.2, 146.2, 144.1, 135.6, 133.7, 133.2, 131.7, 129.6, 128.8, 128.6, 128.4, 126.4, 124.2, 114.8, 63.5, 34.4 2,5-Dimethylsulfanyl-4-(2-benzoyloxyethylsulfanyl )-1,3- (Calc.for C32H27NO6S4: C, 59.15; H, 4.19; N, 2.15; O, 14.77; dithiole 18b. Quantitative yield; the crude product was immedi- S, 19.73. Found: C, 59.02; H, 4.39; N, 2.26; O, 15.20; S, 19.87%); ately used in the subsequent step (synthesis of 19b) without m/z (EI) (%) 649 (M+, 11), 149 (100), 105 (93), 77 (47); further characterization.nmax(KBr)/cm-1 1731, 1719 (CO), 1537, 1333 (NO2). Synthesis of 22 Synthesis of 19a,b Hexafluorophosphoric acid solution (1.97 g, 8 mmol, 60%) was A solution of 21 (1.2 mmol) and KOH (12 mmol) in a mixture of THF (10 ml ), MeOH (5 ml) and H2O (1 ml ) was refluxed added dropwise at 0 °C to a solution of 18a or 18b in acetic anhydride (10 ml ).The mixture was stirred for 10 min and for 1 h. The solution was diluted in CH2Cl2, washed with water and dried (MgSO4). The solvent was evaporated and ethyl acetate (20 ml ) was added. Stirring was maintained for 15 min before adding diethyl ether (100 ml). The resulting the residue was chromatographed over silica gel (ethyl acetate–CH2Cl2 151 as eluent).Compound 22 was obtained precipitate was filtered and washed twice with anhydrous diethyl ether . as a black powder. J. Mater. Chem., 1998, 8(5), 1185–1192 11912 For a review about tetrathiafulvalene chemistry: J. Garin, Adv. 5-[4,5-Bis(2-hydroxyethylsulfanyl)-1,3-dithiol-2-ylidene]-1- Heterocyclo Chem., 1995, 62, 249.(4-nitrophenyl )penta-1,3-diene 22. Yield 79%, mp 137–141 °C; 3 See for instance: (a) H. E. Katz, K. D. Singer, J. E. Sohn, C. W. 1H NMR (CDCl3) 8.17 (d, 2H), 7.49 (d, 2H) 6.98 (d, 1H, 3J= Dirk, L. A. King and H. M. Gordon, J. Am. Chem. Soc., 1987, 109, 8.0, 15.5 Hz), 6.55 (d, 1H, 3J=15.5 Hz), 6.25 (m, 3H), 3.78 (t, 6561; b) M. Blanchard-Desce, I. Ledoux, J. M. Lehn, J.Malthe�te 4H), 3.00 (t, 4H), 2.81 (s, 2H); 13C NMR (CDCl3) 146.3, 144.0, and J. Zyss, J. Chem. Soc., Chem. Commun., 1988, 737; (c) M. Barzoukas, M. Blanchard, D. Josse, J. M. Lehn and J. Zyss, Chem. 135.2, 133.6, 131.5, 129.1, 128.9, 127.7, 126.4, 124.2 115.2, 59.9, Phys., 1989, 133, 323; (d) M. Blanchard-Desce, J. M. Lehn, 39.2 (Calc. for C18H19NO4S4: C, 48.96; H, 4.33; N, 3.17; O, M.Barzoukas, I. Ledoux and J. Zyss, Chem. Phys., 1994, 181, 281; 14.49; S, 29.04. Found: C, 48.44; H, 4.22; N, 3.29; O, 14.95; S, (e) A. K. Y. Jen, V. P. Rao, K. J. Drost, K. Y. Wong and M. P. 29.36%); m/z (EI) (%) 441 (M+, 100), 184 (75), 121 (35); Cava, J. Chem. Soc., Chem. Commun., 1994, 2057; ( f ) D. Lorcy, nmax(Fluorolube)/cm-1 3319 (OH), 1566, 1333 (NO2). A. Robert, S.Triki, L. Ouahab and P. Robin, T etrahedron L ett., 1994, 33, 7341. 4 T. T. Nguyen, Y. Gouriou, M. Salle�, P. Fre` re, M. Jubault, A. Synthesis of 23 Gorgues, L. Toupet and A. Riou, Bull. Soc. Chim. Fr., 1996, 133, Using a similar procedure as for 14, diol 22 was reacted with 301. methacryloyl chloride. Diester 23 was obtained as black 5 Crystal data for compound 8a: C15H18O2S2, M=294.43, triclinic, P19, Z=2, a=8.395(3), b=9.830(4), c=10.909(4) A ° , a=114.09(2), crystals.b=99.99(3), c=96.42(3), V=792.5(6) A ° 3, l=0.71073 A ° . Data collection was carried out by the zig-zag v/2h scan technique 5-[4,5-Bis(2-methacryloyloxyethylsulfanyl)-1,3-dithiol-2- (2<h<25°) on an Enraf–Nonius CAD4 diVractometer. ylidene]-1-(4-nitrophenyl)penta-1,3-diene 23.Yield 58%, mp Conditions of measurements were tmax=40 s, range h, k, l [h (0, 76–79 °C; 1H NMR (CDCl3) 8.17 (d, 2H), 7.48 (d, 2H), 6.98 10); k (-12, 12); l (-13, 13)]. Intensity control reflections were (dd, 1H, 3J=9.9 Hz), 5.48 (m, 2H), 5.61 (s, 1H), 4.35 (q, 4H), measured every 2 h without appreciable decay (0.15%). A total of 3098 independent reflections were collected from which 1153 3.10 (q, 4H), 1.96 (s, 6H); 13C NMR (CDCl3) 170, 146.2, 144.1, corresponded to I>3s(I).Structure refinement: after Lorentz 135.8, 135.6, 133.7, 131.7, 128.8, 128.6, 127.6, 126.6, 126.2, 124.2, polarisation corrections, the structure was solved by direct 114.8, 63.2, 34.3, 18.3; m/z (EI) (%) 577 (M+, 7), 184 (8), 113 methods using the general tangent phasing procedure (GENTAN), (100), 69 (29); nmax(KBr)/cm-1 1711 (CO), 1528, 1330 (.which revealed all the non-hydrogen atoms. After anisotropic refinement of S, O and C atoms, the coordinates of the H atoms Synthesis of 24 were generated from the molecular geometry. The whole structure was refined by full-matrix least-squares techniques (refinement on Using a similar procedure as for 5a,b, aldehyde 20b (1 mmol) F, x, y, z, Uij for S, O and C atoms, x, y, z, and U fixed for H was reacted with dimethyl (5-nitro-2-thienyl )methylphosphon- atoms). 172 variables for 1153 observations, with the resulting R= 0.073, Rw=0.078. All the calculations were performed using the ate (1.1 mmol) as the Wittig–Horner reagent in the presence XTAL 3.2 package. of BunLi (=1.1 equiv., 1.6 M in hexane). 6 (a) D. N. Beratan, ACS Symp. Ser., 1991, 455, 89; (b) S. R. Marder, C. B. Gorman, L. T. Cheng and B. G. Tiemann, Proc. SPIE, 1993, 5-[4-(2-Benzoyloxyethylsulfanyl)-5-methylsulfanyl-1,3- 1775, 19. dithiol-2-ylidene]-1-(5-nitro-2-thienyl )penta-1,3-diene 24. Yield 7 S. R. Marder, C. B. Gorman, B. G. Tiemann and L. Cheng, J. Am. 51%, black powder; m/z (EI) (%) 521 (M+, 20), 489 (10), 149 Chem. Soc., 1993, 115, 3006. 8 Crystal data for compound 12: C20H14S3N4, M=406.55, mono- (100), 105 (76), 77 (47). clinic, P21/c, Z=4, a=10.856(2), b=12.447(3), c=14.995(13) A ° , b=99.69(3)°, V=1997(2) A ° 3, l=0.71073 A ° . Data collection was Synthesis of 25 carried out by the zig-zag v/2h scan technique (2<h<30°) on an Enraf–Nonius Mach III diVractometer. Conditions of measure- Using a similar procedure as for 22, ester 24 (1.2 mmol) was ments were tmax=40 s, range h, k, l [h (0, 15); k (0, 17); l (-21, 21)].hydrolyzed to alcohol 25. Intensity controls without appreciable decay (0.2%) gave 3801 reflections from which 2069 were independent with I>3s(I). 5-[4-(2-Hydroxyethylsulfanyl)-5-methylsulfanyl-1,3-dithiol- Structure refinement: after Lorentz and polarisation corrections, 2-ylidene]-1-(5-nitro-2-thienyl )penta-1,3-diene 25.Yield 60%, the structure was solved by direct methods (SIR) which revealed all the non-hydrogen atoms. After anisotropic refinement of all the dark violet powder; 1H NMR (CDCl3) 7.79 (d, 1H, 3J=4.2 Hz), non-hydrogen atoms, the coordinates of the H atoms were deter- 6.85 (d, 1H, 3J=4.2 Hz), 6.83 (dd, 1H, 3J=10.6, 15.1 Hz), 6.53 mined from the HYDRO program.The whole structure was (d 1H, 3J=15.1 Hz), 6.28 (m, 1H), 6.15 (m, 2H), 3.74 (m, 2H), refined by full-matrix least-squares techniques (use of F magnitude; 2.96, 2.94 (2t, 2H), 2.48, 2.45 (2s, 3H), 2.37 (t, 1H); 13C NMR Uij for C, S and N atoms, x, y, z and B fixed for H); 244 variables (CDCl3) 151.1, 137.5, 134.4, 132.6, 129.9, 127.4, 124.1, 122.2, for 2069 observations, weighting v=1/s(F0)2=[s2(I)+(0.04 114.5, 59.9, 39.0, 19.0, 18.9; m/z (EI) (%) 417 (M+, 100), 385 F02)2]-1/2 with the resulting R=0.048, Rw=0.062.All the calculations were performed using the MOLEN package. Full (38), 249 (40), 204 (45), 190 (60), 147 (67), 135 (62), 103 (68); Crystallographic details, excluding structure factors, have been nmax(KBr)/cm-1 3419 (OH), 1525, 1320 (NO2). deposited at the Cambridge Crystallographic Data Centre (CCDC). See Information for Authors, J.Mater. Chem., 1998, Issue The authors thank S. Brasselet for her kind help in EFISH 1. Any request to the CCDC for this material should quote the full data processing, as well as Professor J. P. Busnel for polymer literature citation and the reference number 1145/91. characterization. This work was partially supported by the 9 J. L. Oudar, J. Chem. Phys., 1977, 67, 446. 10 For methacrylate NLO active polymers, see for instance: (a) C. Xu, grant ‘Marche� d’e�tudes’ CNET No. 926B040. Financial support B. Wu, O. Todorova and L. R. Dalton, Macromolecules, 1993, 26, from DGICYT (PB94–0577) is gratefully aknowledged. 5303; (b) J. Y. Lee and H. J. Lee, Polym. Bull., 1997, 38, 265; (c) D. W. Kim, S. Hong, S. Y. Park and N. Kim, Bull. Korean Chem. Soc., 1997, 18, 198. References 11 (a) V. Y. Khodorkovsky, J. Y. Becker and J. Y. Bernstein, Synthesis, 1992, 1071; (b) J. S. Zambounis and C. W. Mayer, T etrahedron 1 (a) Nonlinear Optical Properties of Organic Molecules and Crystals, L ett., 1991, 32, 2737. ed. D. S. Chemla and J. Zyss, Academic Press, Orlando, 1987; (b) 12 (a) T. K. Hansen, T. Jorgensen, F. Jensen, P. H. Thygesen, Molecular Nonlinear Optics : Materials, Physics and Devices, ed. K. Christiansen, M. B. Hursthouse, M. E Harman, M. A. Malik, J. Zyss, Academic Press, Boston, 1994; (c) Nonlinear Optics of B. Girmay, A. E. Underhill, M. Begtrup, J. D. Kilburn, K. Belmore, Organic Molecules and Polymers, ed. H. S. Nalwa and S. Miyata, P. RoepstorV and J. Becher, J. Org. Chem., 1993, 58, 1359; (b) CRC Press, 1994; (d) Introduction to Nonlinear Optical EVects in A. J. Moore and M. R. Bryce, J. Chem. Soc., Chem. Commun., Molecules and Polymers, ed. N. Prasad and D. J. Williams, Wiley, 1991, 1639. New York, 1991; (e) L. R. Dalton, A. W. Harper, R. Ghosn, W. H. Steier, M. Ziari, H. Fetterman, Y. Shi, R. V. Mustacich, K. Y. Jen and K. J. Shea, Chem.Mater., 1995, 7, 1060. Paper 7/09055B; Received 17th December, 1997 1192 J. Mater. Chem., 1998, 8(5), 1185–

ISSN:0959-9428    

DOI:10.1039/a709055b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials A new class of second-order non-linear optical material: stilbazolium benzimidazolate derived from alkylsulfonyl substituted stilbazole Nobukatsu Nemoto,a Jiro Abe,b Fusae Miyata,a Yasuo Shiraib and Yu Nagase*a aSagami Chemical Research Center, 4–4-1 Nishi-Ohnuma, Sagamihara, Kanagawa 229, Japan bDepartment of Photo-optical Engineering, Faculty of Engineering, T okyo Institute of Polytechnics, 1583 Iiyama, Atsugi, Kanagawa 243–02, Japan A novel stilbazolium benzimidazolate derivative, i.e. 2-(4-{2-[4-(octylsulfonyl )phenyl]ethenyl}pyridinio)benzimidazolate 4a, was prepared by the quaternization reaction of 4-{2-[4-(octylsulfonyl)phenyl]ethenyl}pyridine with 2-chlorobenzimidazole, followed by deprotonation with aqueous ammonia. Poly(methyl methacrylate) (PMMA) thin films containing 10 or 20 mass% of 4a were obtained by spin-coating from their THF solutions on an ordinary cover glass substrate.Second-harmonic generation (SHG) measurements of the obtained thin films were carried out by the Maker fringe method using a Q-switched Nd5YAG laser (1064 nm) as an exciting beam after corona-poling. A poled PMMA film containing 10 or 20 mass% of 4a exhibited a secondorder non-linear optical (NLO) coeYcient, d33, of 7.6 or 11 pm V-1, respectively, which was much larger than the d33 value of a PMMA thin film containing 10 mass% of 2-[4-(2-phenylethenyl)pyridinio]benzimidazolate 4c (d33 1.6 pm V-1) or 2-{4-[2-(4- octyloxyphenyl)ethenyl]pyridinio}benzimidazolate 4d (d33 0.51 pm V-1).There were no significant diVerences in linear absorption properties of PMMA films containing 4a, 4c or 4d.The introduction of an octylsulfonyl group at the 4¾-position of the stilbazole moiety increases the second-order NLO coeYcient. Second-order non-linear optical organic molecules, which have polymer film due to dipole-dipole interactions, which results in the temporal or thermal relaxation of second-order NLO been the subject of many reports, are aromatic compounds with a pair of electron-donor and electron-acceptor groups at activity.It may be possible for pyridinium betaine compounds to overcome this problem, due to their characteristics as p-conjugating sites, so-called classical D-p-A system molecules. 1,2 Recently, various types of NLO molecules classified mentioned above.We have also investigated poled thin films of some pyridinium or stilbazolium benzimidazolates dispersed into non-classical molecular systems have been developed3 for the improvement of the physical properties of NLO molecules in poly(methyl methacrylate) (PMMA) via Maker fringe measurements.9 However, the limited solubility and centro- and for solving the problem of the trade-oV between optical non-linearity and cutoV wavelength, which is generally defined symmetric aggregation of pyridinium betaines in polymeric matrixes seemed to inhibit the increase of their second-order as the wavelength where the value of the first deviation for the absorbance becomes 0.Heterocyclic betaines have received NLO susceptibility. To solve these problems, we have prepared two kinds of much attention because of their unusually high dipole moments, which are ascribed to their zwitterionic character; novel stilbazolium benzimidazolates 4a and 4b, the phenyl groups of which are substituted by electron-acceptor groups, this is confirmed by the fact that they exhibite negative solvatochromism.4 Pyridinium or stilbazolium benzimidazol- i.e.octylsulfonyl or perfluorooctylsulfonyl groups, which would cause not only an increase in the b value but also render them ates, which consist of a negatively charged aromatic donor group and a positively charged aromatic acceptor group, are more soluble in organic solvents owing to their decreased dipole moment in the ground state. Additionally, a poly(methyl heterocyclic betaines.The NLO activities of the present pyridinium or stilbazolium benzimidazolates are attributed to short- methacrylate) (PMMA) thin film containing 4a was prepared, the linear optical and second-order NLO properties of which range charge transfer through the s-bond from the charged aromatic donor group to the charged aromatic acceptor group. are described. We have revealed that some pyridinium or stilbazolium benzimidazolates classified as non-classical molecular systems are applicable as second-order non-linear optically active molecules from theoretical investigations5 and hyper-Rayleigh scattering measurements.6 One distinct characteristic of pyridinium betaine compounds is that the value of the first hyperpolarizability, b, is enlarged with decreasing dipole moment.7 Namely, from theoretical calculations,8 the introduction of an electron-acceptor substituent at the 4¾-position of the stilbazole moiety in stilbazolium benzimidazolate decreased the dipole moment in the ground state, but increased the b value compared with stilbazolium benzimidazolate without a substituent at the 4¾-position of the stilbazole moiety. In many Experimental cases, an increase in b for classical D-p-A system molecules is Materials accompanied by an increase in the dipole moment.2 A large polarizability often brings temporal or thermal relaxation to N,N-Dimethylformamide (DMF) was distilled over CaH2 the noncentrosymmetric alignment of NLO-phores in a poled under reduced pressure.Butan-1-ol and triethylamine (Wako Pure Chemical Industries, Ltd.) were used after distillation over CaH2. 4-Bromobenzenethiol, 1-bromooctane (Tokyo * E-mail: yunagase@alles.or.jp J. Mater. Chem., 1998, 8(5), 1193–1197 1193Kasei Kogyo Co., Inc.), palladium(II) acetate, 30% aqueous column packed with silica gel with hexane–ethyl acetate (751) as eluent. Evaporation of the solvent aVorded the title com- hydrogen peroxide and acetic acid (Kanto Chemical Co., Inc.) pound 2a (14.83 g, 94.5%) as colourless crystals: dH(CDCl3, were commercially available and used as received. 4- 90 MHz) 0.86 [t, J 6.9, 3H, CH3(CH2)7], 1.1–2.0 [m, 12H, Vinylpyridine was distilled under reduced pressure just before CH3(CH2)6CH2], 3.0–3.3 (m, 2H, CH2SO2), 7.73 (s, 4H, phen- use. 2-Chlorobenzimidazole was prepared by modifying the ylene protons); nmax /cm-1 3090, 3065, 2955, 2925, 2850, 1910, method reported by Harrison et al.10 PMMA (Mn54.3×105, 1780, 1650, 1580, 1470, 1410, 1390, 1325, 1315, 1305, 1280, determined by gel permeation chromatography; Tg 101 °C 1245, 1215, 1205, 1180, 1145, 1085, 1065, 1010, 985, 960, determined by diVerential scanning calorimetry) was purchased 930, 895, 855, 820, 795, 770, 735, 725, 620, 565, 550, 530, from Nacalai tesque, Inc.and used as received. 495, 455; m/z 334 (M++2), 332 (M+), 317, 315, 291 Instrumentation [(M++2)-(C3H7)], 289 [M+-(C3H7)], 249, 247, 234, 232, 223, 221, 203, 201, 197, 195, 185, 183, 171, 169, 157 UV-VIS absorption spectra were measured by transmission [(M++2)-(C3H7SO2)], 155 [M+-(C3H7SO2)], 141, 112, 93, on a Shimadzu Model U-2100 spectrophotometer. 1H NMR 71, 57, 43, 29 (Found: C, 50.45; H, 6.35.Calc. for C14H21BrO2S: spectroscopy was conducted with a Hitachi R-90H FT NMR C, 50.29; H, 6.32%). (90 MHz) spectrometer or a Bruker AM-400 FT NMR Compound 2b was prepared via a similar method as for 2a (400 MHz) spectrometer; J values are given in Hz. IR Spectra using 1b instead of 1a. The product yield was 87%: dH(CDCl3, were measured by transmission on a Jasco A-202 IR spec- 90 MHz) 7.86 (s, 4H, phenylene protons); nmax/cm-1 3095, trometer.Mass spectrometry was conducted on a Hitachi 1575, 1470, 1395, 1365, 1330, 1285, 1205, 1175, 1150, 1080, Mass Spectrometer M-80B by electron ionization method. 1070, 1010, 935, 830, 800, 750, 705, 660, 645, 615, 595, 550, DiVerential scanning calorimetry (DSC) measurements were 530; m/z (SIMS) 641 (M++3), 639 (M+ + 1) (Found: C, 26.2; carried out on a Shimadzu Model DSC-50 under a helium H, 0.4.Calc. for C14H4BrF17 O2S: C, 26.31; H, 0.63%). flow rate of 20 ml min-1 and a heating rate of 10 °C min-1. 4-{2-[4-(Octylsulfonyl )phenyl]ethenyl}pyridine 3a 4-(Octylthio)bromobenzene 1a Under an argon atmosphere, a mixture of 2a (9.998 g, Under an argon atmosphere, 4-bromobenzenethiol (9.45 g, 30.0 mmol), 4-vinylpyridine (4.206 g, 40.0 mmol), triethylamine 50.0 mmol) in dry DMF (10 ml ) was added dropwise to sodium (3.036 g, 30.0 mmol), palladium (II ) acetate (0.203 g, 0.90 mmol) hydride (2.40 g, 60.0 mmol, 60% in mineral oil ) suspended in and 15 ml of dry acetonitrile was degassed, refluxed for 72 h dry DMF (30 ml ) in an ice bath.The reaction mixture was and cooled. To this reaction mixture was added chloroform stirred at ambient temperature for 1 h, and 1-bromooctane and water. The crude product was extracted with chloroform, (10.62 g, 55.0 mmol) was added dropwise. After the reaction and the organic layer was dried over anhydrous sodium sulfate. mixture was stirred at ambient temperature for 2 h, DMF was The chloroform was evaporated, and the residue was purified evaporated under reduced pressure. Water and ethyl acetate by column chromatography, using a column packed with silica were added to the residue, and the organic layer was washed gel with hexane–ethyl acetate (251) as eluent.Finally, recryswith water. The organic layer was dried with anhydrous tallization of the product from of ethyl acetate–hexane aVorded sodium sulfate, and the solvent was evaporated to dryness.the title compound 3a with a yield of 8.093 g (75.5%) as The crude product was purified by column chromatography, white crystals: dH(CDCl3, 400 MHz) 0.86 [t, J=7.0, 3H, using a column packed with silica gel with hexane as eluent. CH3(CH2)2], 1.2–1.3 [m, 8H, CH3(CH2)2CH2], 1.36 [quintet, The product yield was 14.97 g (99%) as a colourless liquid: J 7.0, 2H, CH3(CH2)4CH2], 1.7–1.8 [m, 2H, CH3(CH2)2CH2], dH(CDCl3, 90 MHz) 0.88 [t, J 7.0, 3H, CH3(CH2)7], 1.1–2.0 3.1 (m, 2H, CH2SO2), 7.16 (d, J 16.4, 1H, NCH-pyridyl), 7.33 [m, 12H, CH3(CH2)6CH2], 2.88 (t, J 7.0, 2H, CH2S), 7.22 (dt, (d, J 16.4, 1H, NCH-phenylene), 7.40 (dd, J 1.6, 4.6, 2H, J 2.2, 8.8, 2H, phenylene protons), 7.39 (dt, J 2.2, 8.8, 2H, pyridyl protons), 7.71 (dt, J 1.7, 8.5, 2H, phenylene protons), phenylene protons); nmax/cm-1 2955, 2925, 2855, 1885, 1630, 7.92 (dt, J 1.7, 8.5, 2H, phenylene protons), 8.63 (dd, J 1.6, 4.6, 1565, 1475, 1385, 1305, 1265, 1240, 1180, 1095, 1070, 1005, 805, 2H, pyridyl protons); nmax /cm-1 3050, 3030, 2980, 2955, 2925, 725, 505, 480; m/z 302 (M++2), 300 (M+), 203 1930, 1670, 1635, 1595, 1565, 1550, 1495, 1465, 1380, 1300, [(M++2)-(C7H15)], 201 [M+-(C7H15)], 188, 186, 122, 108, 1285, 1260, 1245, 1215, 1195, 1140, 1120, 1090, 1045, 1015, 980, 82, 71, 57, 55, 43, 41, 29 (Found: C, 55.6; H, 7.1.Calc. for 970, 870, 830, 800, 770, 750, 725, 705, 665, 620, 590, 570, 565, C14H21BrS: C, 55.81; H, 7.03%). 545, 530, 500, 480, 445, 415; m/z 357 (M+), 328 [M+-(C2H5)], Compound 1b was prepared via a similar method as for 1a 314 [M+-(C3H7)], 292, 270, 265, 245, 228, 208, 195, 181, 160, using perfluorooctyl iodide instead of 1-bromooctane. The 152, 138, 127, 69, 57, 43, 28 (Found: C, 70.6; H, 7.6; N, 4.0; S product yield was 86% as colourless crystals.dH(CDCl3, 9.0. Calc. for C21H27NO2S: C, 70.55; H, 7.61; N, 3.92; S, 8.97%). 90 MHz) 7.54 (s, 4H, phenylene protons); nmax/cm-1 2925, Compound 3b was prepared via a similar method as for 3a 1905, 1640, 1570, 1475, 1385, 1370, 1325, 1245, 1200, 1150, using 2b instead of 2a. The product yield was 35.9%: dH(CDCl3, 1115, 1100, 1090, 1070, 1010, 935, 820, 800, 780, 745, 730, 710, 400 MHz) 7.24 (d, J 16.4, 1H, NCH-pyridyl), 7.35 (d, J 16.4, 675, 655, 600, 560, 530, 510, 490; m/z 608 (M++2), 606 1H, NCH-phenylene), 7.41 (dd, J 1.5, 4.6, 2H, pyridyl protons), (M+), 589 [(M++2)-F], 587 (M+-F), 508, 239 7.80 (d, J 8.5, 2H, phenylene protons), 8.05 (d, J 8.5, 2H, [(BrPhSCF2+)+2], 237 (BrPhSCF2+), 189 [(BrPhS+)+2], phenylene protons), 8.66 (dd, J 1.6, 4.6, 2H, pyridyl protons); 187 (BrPhS+), 169 [(C3F7)+], 158, 131, 119 (C2F7+), 108, 82, nmax /cm-1 3025, 3010, 1595, 1570, 1555, 1495, 1415, 1375, 69 (CF3+), 55, 43, 28 (Found: C, 27.7; H, 0.7.Calc. for 1330, 1260, 1230, 1160, 1145, 1120, 1085, 1055, 1015, C14H4BrF17S: C, 27.49; H, 0.43%). 990, 975, 955, 940, 880, 860, 830, 805, 750, 710, 695, 680, 660, 605, 585, 555, 515, 480; m/z 663 (M+), 644 (M+-F), 4-(Octylsulfonyl )bromobenzene 2a 244 [M+-(C8F17)], 228, 196 [M+-(C8F17SO)], 180 [M+-(C8F17SO2)], 169 [(C3F7)+], 152, 131, 119 (C2F5+), A mixture of 1a (14.19 g, 47.1 mmol), acetic acid (100 ml) and 90, 69 (CF3+), 51 (Found: C, 37.9; H, 1.3; N, 2.1.Calc. for 30% aqueous hydrogen peroxide (16.02 g, 141.3 mmol) was C21H10NO2SF17: C, 38.02; H, 1.52; N, 2.11%). refluxed for 1 h. The reaction mixture was poured into 300 ml of saturated aqueous sodium hydrogen carbonate.The crude 2-(4-{2-[4-(Octylsulfonyl )phenyl]ethenyl}pyridinio)benzproduct was extracted with ethyl acetate, and the combined imidazolate 4a ethyl acetate extracts were dried over anhydrous sodium sulfate. The residue resulting from evaporation of the ethyl Under an argon atmosphere, a mixture of 2-chlorobenzimidazole (1.526 g, 10.0 mmol), 3a (3.575 g, 10.0 mmol) and 5 ml of acetate was purified by column chromatography using a 1194 J.Mater. Chem., 1998, 8(5), 1193–1197dry butan-1-ol was stirred at 100 °C for 12 h and then cooled. This reaction mixture was poured into 500 ml of diethyl ether, and the resulting precipitate was collected by filtration. The residual solid was washed with diethyl ether and dissolved in 100 ml of methanol at 60 °C.The solution was treated with 10 ml of aqueous ammonia at 60 °C. To this mixture was added 400 ml of water. The resulting precipitate was collected by filtration. The crude product was purified by recrystallization from acetone–methanol aVording the title compound 4a with a yield of 2.77 g (58%) as red–brown crystals: dH(CDCl3, 400 MHz) 0.87 [t, J 7.1, 3H, CH3(CH2)7] 1.2–1.3 [m, 8H, CH3(CH2)4CH2], 1.38 [quintet, J 7.1, 2H, CH3(CH2)4CH2], 1.7–1.8 [m, 2H, CH3(CH2)5CH2], 3.1–3.2 (m, 2H, CH2SO2), 7.10–7.16 (m, 2H, benzimidazolate protons), 7.18 (d, J 16.3, 1H, NCH-pyridyl), 7.55 (d, J 16.4, 1H, NCH-phenylene), 7.62–7.68 (m, 2H, benzimidazolate protons), 7.72 (d, J 7.2, 2H, pyridyl protons), 7.78 (d, J 8.4, 2H, phenylene protons), 8.00 (d, J 8.4, 2H, phenylene protons), 9.83 (d, J 7.2, 2H, pyridyl protons); nmax/cm-1 3125, 3055, 2930, 2855, 1620, 1565, 1555, 1500, 1465, 1410, 1395, 1320, 1310, 1270, 1190, 1145, 1115, 1090, 1045, 1015, 1000, 970, 955, 900, 880, 845, 810, 770, 745, 730, 710, 660, 620, 600, 555, 545, 530; m/z 475 (M++2), 396, 384, 357, 299, 284, 273, 259, 220, 209, 183, 133, 118, 105, 90, Scheme 1 Reagents and conditions: i, NaH, DMF, 0 °C, 1 h; ii, 79, 64, 51, 39 (Found: C, 71.3; H, 6.7; N, 9.0; S 6.7.Calc. for Br(CH2)8Br or I(CF2)8F, DMF, room temp., 2 h; iii, H2O2, AcOH, reflux, 1 h; iv, 4-vinylpyridine, Pd(OAc)2, Et3N, CH3CN, reflux, 72 h; C28H31N3O2S: C, 71.01; H, 6.60; N, 8.87; S, 6.77%). v, 2-chlorobenzimidazole, BuOH, 12–24 h; vi, aq. NH3, MeOH, 60 °C, Compound 4b was prepared via a similar method as for the 30 min preparation of 4a using 3b instead of 3a The product yield was 63%: dH(CDCl3, 400 MHz) 7.14–7.22 (m, 3H, benzimidazolate protons and NCH-pyridyl), 7.38 (d, J 15.2, 1H, NCHzole and novel stilbazole derivatives 3a and 3b, which were phenylene), 7.68–7.72 (m, 2H, benzimidazolate protons), 7.90 prepared by the Heck reactions of 4-vinylpyridine with 4- (d, J 8.5, 2H, phenylene protons), 7.93 (d, J 7.2, 2H, pyridyl (octylsulfonyl )bromobenzene 2a and 4-(perfluorooctylsulfonprotons), 8.14 (d, J 8.5, 2H, phenylene protons), 10.02 (d, J 7.2, yl )bromobenzene 2b, respectively.Stilbazolium benzimidazol- 2H, pyridyl protons); nmax/cm-1 3125, 3075, 3050, 1620, 1590, ates 4a and 4b are soluble in common polar organic solvents 1570, 1555, 1500, 1470, 1450, 1410, 1375, 1330, 1305, 1215, such as chloroform, methanol, ethanol, acetone, THF and so 1175, 1150, 1125, 1085, 1055, 1030, 1010, 970, 955, 880, 845, on, however, the solubility of 4a was much better than that of 810, 750, 710, 680, 660, 645, 600, 580, 555, 525, 490; m/z 779 4b in the common organic solvents mentioned above.The (M+), 715, 663, 553, 489, 346, 296 [M+-(C8F17SO2)], 244, decomposition temperatures of 4a and 4b were estimated from 228, 209, 196, 180, 169 [(C3F7)+], 152, 131, 119 (C2F5+), 100, diVerential scanning calorimetry (DSC) measurements. Melting 85, 69 (CF3+), 64, 51, 48 (Found: C, 43.0; H, 1.6; N, 5.3. Calc. was observed from 232 °C in the case of 4a with thermal for C28H14N3O2SF17: C, 43.15; H, 1.81; N, 5.39%).decomposition occurring at 235 °C on a heating scan; however, no melting was observed for 4b, while thermal decomposition SHG Measurement occurred at 237 °C. The thermal stability of 4a and 4b seems to be compatible with the processing temperatures of promising PMMA thin films containing 10 or 20 mass% of 4a were NLO polymers.13 obtained by spin-coating on an ordinary cover glass plate at Optical-quality thin films of PMMA containing 10 or 20 a rate of 2000 rpm from a THF solution which contained mass% of 4a could be obtained by spin coating on an ordinary PMMA and 10 or 20 mass% of 4a with respect to PMMA.glass substrate from a THF solution which contained PMMA The thickness of the obtained film was determined to be and 10 or 20 mass% of 4a with respect to PMMA.However, ca. 0.5 mm. Poling was normal to the surface by corona disoptical- quality thin films of PMMA containing 10 mass% of charge. The distance of the tungsten needle from the surface 4b could not be obtained, because of the poor solubility in was 25 mm. The needle side was set to 10 kV negative to an organic solvents of 4b, possibly owing to the eVects of the aluminum heating plate.After 20 min of poling at 110 °C, the perfluorooctyl moiety. On the other hand, other stilbazolium film was cooled to ambient temperature with continuous benzimidazolate derivatives 4c (4¾-position not substituted) corona poling. and 4d (4¾-position substituted with an octyloxy moiety could The second harmonic generation (SHG) at 532 nm was be dissolved in PMMA up to 10 mass% with respect to measured in transmission by means of the Maker fringe PMMA. Taking these results into account, it can be seen that method,11 using a Q-switched Nd5YAG laser (Spectron the introduction of an octylsulfonyl group at the 4¾-position SL404G, l=1064 nm, 10 Hz repetition rate, 6 ns pulse durof the stilbazole moiety contributes to an improvement in ation) as the exciting light source.Detailed experimental and processability. calculating procedures are described in our previous report.12 As a reference sample we used a 1 mm-thick y-cut quartz Optical properties of PMMA thin films containing stilbazolium (d11=0.46 pm V-1). benzimidazolate derivatives Results and Discussion The optical properties of betaine 4a in PMMA are summarized in Table 1.We defined the cutoV wavelength (lcutoff) as the Preparation of novel stilbazolium benzimidazolate derivatives wavelength where the value of the first deviation for absorbance becomes 0. Fig. 1 shows the UV–VIS spectrum of 20 mass% The synthetic pathways to novel stilbazolium benzimidazolate derivatives 4a and 4b are described in Scheme 1.Stilbazolium of 4a dispersed in a PMMA thin film, lCT of which is 426 nm. The present lCT means that the wavelength where the benzimidazolate derivatives 4a and 4b were prepared by the formation of the betaine structure between 2-chlorobenzimida- absorbance becomes maximal is in the visible region. The lCT J. Mater. Chem., 1998, 8(5), 1193–1197 1195Table 1 Linear and non-linear optical properties for spin-coated films of PMMA containing stilbazolium benzimidazolate derivatives run compound content of betaine/mass% lCT/nma lcutoff/nm d33/pm V-1 1 4a 10 433 610 7.6 2 4a 20 426 610 11 3 4cb 10 430 600 1.6 4 4db 10 440 600 0.51 alCT=the wavelength in the visible region where the absorbance becomes maximal.bFrom ref. 9(b). ively. In the case of run 4, the centrosymmetric aggregation of 4d in PMMA, which is probably promoted by the large polarizability of 4d,8 provides the lowest order parameter in the present series.The order parameter in the case of run 1 was lower than that in the case of run 3. Our previous study using ab initio and INDO/S calculations6 revealed that the dipole moment of a stilbazolium benzimidazolate derivative, the 4¾-position of which is substituted with a nitro moiety, is smaller than that of 4c by ca. 7.5 D. According to this finding, the dipole moment of 4a in the ground state was expected to be smaller than that of 4c. Thus, the electric poling was more eVective in the case of run 3 than in the case of run 1. The second harmonic generation (SHG) of the thin film was measured in transmission by means of the Maker fringe method.11,12 A Q-switched Nd5YAG laser (Spectron SL404G, l=1064 nm, 10 Hz repetition rate, 6 ns pulse duration) was used as the exciting light source.The p-polarized laser beam was chosen using a l/4 wave plate and a linear polarizer. Fig. 2 describes the relationship between SH light intensity and the incident angle of the exciting beam for the spin-coated film of PMMA containing 20 mass% of 4a obtained after corona Fig. 1 UV–VIS absorption spectra of 10 mass% of 4a dispersed in a poling. PMMA thin film; (a) before corona poling, (b) after corona poling The second-order NLO coeYcients, d33, of the spin-coated at 110 °C films were determined by the mean-square method15 using the relationship of SH light intensity and the incident angle of an of the PMMA thin film containing 10 mass% of 4a was exciting beam proposed by Jerphagnon and Kurtz.11 It has 433 nm.The blue-shift of lCT in the case of the PMMA thin been reported9 that poled films of PMMA containing 10 film containing 20 mass% of 4a is probably due to the increase mass% of 4c or 4d exhibit a d33 of 1.6 or 0.51 pm V-1, in the content of 4a inducing the enlargement of the polariz- respectively.In the present case, the d33 value of PMMA ability around the chromophores. An increase in the polarity containing 10 or 20 mass% of 4a is 7.6 or 11 pm V-1, of the medium has been known to induce the blue-shift of a respectively. Namely, the d33 value of PMMA containing 10 maximum absorption band of pyridinium betaines.4 The lCT mass% of 4a is 5-fold larger than that of PMMA containing of the stilbazolium benzimidazolate without a substituent, 4c, 10 mass% of 4c, although the order parameter in the case of dispersed in a PMMA thin film has been reported9b to be run 1 was lower than that in the case of run 3, as mentioned 430 nm, which is comparable to the lCT of the present stilbazol- above.This result is due to the substituent eVect of the ium benzimidazolate 4a.Namely, the introduction of an octylsulfonyl group at the 4¾-position of the stilbazole moiety has no significant eVect on lCT. It is generally accepted that the introduction of a strong electron-acceptor group into classical D-p-A molecular systems is accompanied by the red-shift of the lCT. Such red-shifts of the lCT were not observed in the stilbazolium benzimidazolate derivatives investigated.The absorbance around lCT decreased after the sample was poled at 110 °C for 20 min, applying the voltage of 4 kV cm-1 with the corona poling method as shown in Fig. 1, indicating the promotion of chromophore orientation by electric poling. Similar results were obtained in the case of 20 mass% of 4a dispersed in a PMMA thin film.Additionally, a blue-shift of the maximum absorption in the visible region was observed, which could be interpreted as resulting from the polarity of the environment around the chromophores being increased due to the noncentrosymmetric alignment of 4a, as mentioned above. The order parameters of poled samples were estimated using spectroscopic measurements at lCT and eqn.(1),14 P =1-A/A0 (1) where P is the order parameter, and A0 and A are the absorbance lCT before and after poling at 110 °C for 20 min, Fig. 2 Relationship between SH light intensity and the incident angle respectively. The order parameters in the cases of runs 1, 3 of an exciting beam for 10 mass% of 4a dispersed in a PMMA thin film after corona poling at 110 °C and 4 (Table 1) were estimated as 0.14, 0.19 and 0.10, respect- 1196 J.Mater. Chem., 1998, 8(5), 1193–1197J. Hulliger, M. Flo� rsheimer, P. Kaatz and P. Gu� , Gordon and octylsulfonyl moiety. The introduction of the octylsulfonyl Breach Publishers, New York, 1995, vol. 1; (c) Polymers for group at the 4¾-position of the stilbazole moiety is of value not Second-Order Nonlinear Optics, ACS Symposium Series 601, only for improving the processability of stilbazolium benzimided.G. A. Lindsay and K. D. Singer, American Chemical Society, azolates but also for increasing their second-order NLO suscep- Washington, DC, 1995; (d) Molecular Nonlinear Optics: Materials, tibility. On the other hand, the d33 value of a poled PMMA Physics and Devices, ed. J.Zyss, Academic Press, Boston, 1994; (e) D.M. Burland, R. D. Miller and C. A. Walsh, Chem. Rev., 1994, film containing ca. 8 mass% of Disperse Red 1 (DR1, 2-{[N- 94, 31; ( f ) L. R. Dalton, A. W. Harper, R. Ghosn, W. H. Steier, ethyl-4-(4-nitrophenyl)azo]anilino}ethanol), which is a typical H. Fetterman, Y. Shi, R. V. Mustacich, A. K.-Y. Jen and K. J. Shea, example of a classical D-p-A molecule (lCT 490 nm) has been Chem.Mater., 1995, 7, 1060. reported16 to be ca. 8.5 pm V-1 using a Nd5YAG laser (l= 2 (a) J. L. Oudar and D. S. Chemla, J. Chem. Phys., 1977, 66, 2664; 1064 nm) as an exciting source. The present PMMA film (b) J. L. Oudar and J. Zyss, Phys. Rev. A, 1982, 26, 2016. containing 10 mass% of 4a exhibited a shorter lCT (433 nm) 3 (a) J. O.Morley, J. Chem. Soc., Faraday T rans., 1994, 90, 1853; (b) C. Serbutoviez, J. F. Nicoud, J. Fischer, J. Ledoux and J. Zyss, and a comparable d33 value (7.6 pm V-1) using the same Chem. Mater., 1994, 6, 1358; (c) M. S. Wong, C. Bosshard, F. Pan exciting light source. and P. Gu� nter, Adv.Mater., 1996, 8, 677; (d) X.-M. Duan, S. Okada, If the preparation of stilbazolium benzimidazolate covalently H.Oikawa, H. Matsuda and H. Nakanishi, Nonlinear Opt., 1996, bound to a polymeric backbone is achieved hereafter, the NLO 15, 119. activity would be expected to increase, because of the uniform 4 Typical review: E. Alcalde, Adv. Heterocycl. Chem., 1994, 60, 197. distribution of the stilbazolium betaine in the matrix as well 5 J. Abe and Y. Shirai, J. Am. Chem. Soc., 1996, 118, 4705. 6 J. Abe, Y. Shirai, N. Nemoto, F. Miyata and Y. Nagase, J. Phys. as the inhibition of aggregation due to polymeric eVects.17 Chem. B, 1997, 101, 576. Studies on this subject are in progress. 7 J. Abe, N. Nemoto, Y. Nagase and Y. Shirai, Chem. Phys. L ett., 1996, 261, 18. 8 J. Abe, Y. Shirai, N. Nemoto and Y. Nagase, J. Phys. Chem. B, Conclusions 1997, 101, 1910. 9 (a) N.Nemoto, J. Abe, F. Miyata, M. Hasegawa, Y. Shirai and The preparation of a novel stilbazolium benzimidazolate Y. Nagase, Chem. L ett., 1996, 851; (b) N. Nemoto, J. Abe, derivative, i.e. 2-(4-{2-[4-(octylsulfonyl)phenyl]ethenyl}pyrid- F. Miyata, Y. Shirai and Y. Nagase, Nonlinear Opt., in the press. inio)benzimidazolate 4a, has been achieved. The introduction 10 D. Harrison, J. T. Ralph and A. C. B. Smith, J. Chem. Soc., 1963, of an octylsulfonyl group at the 4¾-position of the stilbazole 203. moiety is of value not only in improving the processability of 11 J. Jerphagnon and S. K. Kurtz, J. Appl. Phys., 1970, 41, 1667. 12 N. Nemoto, Y. Nagase, J. Abe, H. Matsushima, Y. Shirai and stilbazolium benzimidazolates but also in increasing their N. Takamiya, Macromol. Chem. Phys., 1995, 196, 2237. second-order NLO susceptibilities without significantly influ- 13 P. Boldt, T. Eisentra�ger, C. Glania, J. Go� ldenitz, P. Kra�mer, encing their linear absorption properties. The application of R. Matschiner, J. Rase, R. Schwesinger, J. Wichern and pyridinium heterocyclic betaines in NLO is worthy of notice R. Wortmann, Adv. Mater., 1996, 8, 672. and should lead to the development of a new class of 14 B. Guichard, C. Noe�l, D Reyx and F. Kajzar, Macromol. Chem. Phys., 1996, 197, 2185. second-order NLO materials. 15 N. Nemoto, F. Miyata, Y. Nagase, J. Abe, M. Hasegawa and Y. Shirai, Macromolecules, 1996, 29, 2365. 16 M. A. Mortazavi, A. Knoesen, S. T. Kowel, B. G. Higgins and References A. Dienes, J. Opt. Soc. Am. B, 1989, 6, 733. 17 N. Nemoto, J. Abe, F. Miyata, Y. Shirai and Y. Nagase, J. Mater. 1 Recent books and reviews: (a) Nonlinear Optics of Organic Chem., 1997, 7, 1389. Molecules and Polymers, ed. H. S. Nalwa and S. Miyata, CRC Press, Boca Raton, 1997; (b) Organic Nonlinear Optical Materials, Advances in Nonlinear Optics, ed. C. Bosshard, K. Sutter, P. Pre�tre, Paper 7/08620B; Received 1st December, 1997 J. Mater. Chem., 1998, 8(5), 1193&nda

ISSN:0959-9428    

DOI:10.1039/a708620b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Optochemical HCl gas sensor using substituted tetraphenylporphine– ethylcellulose composite films Katsuhiko Nakagawa,a Kazunari Tanaka,b Takahiro Kitagawa and Yoshihiko Sadaoka*b aDepartment of Industrial Chemistry, Niihama National College of T echnology, Niihama 792, Japan bCenter for Advanced T echnology, Ebara Research Co., L td., Fujisawa 251, Japan Department of Materials Science and Engineering, Faculty of Engineering, Ehime University, Matsuyama 790–77, Japan Composite films of various tetraphenylporphines embedded in ethylcellulose were prepared and their optical response to gaseous HCl was investigated.The absorbance of the Soret and Q-bands for free-base tetraphenylporphines is reversibly sensitive to ppm levels of HCl.The replacement of the para hydrogen in one phenyl group with a hydroxy group is eVective in enhancing the sensitivity of the Q-band region while prolonging response time. In addition, the temperature coeYcient of the sensitivity of TP(OH) (R)3PH2 is lower than that of TPPH2. Under filtered light (>600 nm) a significant deterioration of the sensitivity was not observed for more than 50 d.Recently, various optochemical sensors operating at room (451). The first band oV the column was the 5,10,15,20- tetrakis( p-alkylphenyl)porphine by-product. The third band, temperature have been reported to measure the emission of gaseous pollutants at ppm or ppb concentration levels.1–8 It is which moved very slowly, was eluted with DCM containing ethanol (1%, gradually increasing to 3%) and collected and well known that in nonaqueous media the tetrapyrrolic porphine macrocycle is oxidized in successive monoelectronic concentrated. For further purification, each component was subjected to column chromatography on silica gel, and eluted steps giving monocationic radicals and dications. Furthermore, the amphoteric nature of the porphine molecule permits the with DCM containing ethanol (0.5%, gradually increasing to 5%).Compounds 1–3 were isolated, then recrystallized from formation of acid salts involving the addition of protons to the porphine center. DCM–methanol–n-hexane and identified as follows: Recently, there has been a need for the detection of subppm levels of HCl gas concentrations from adsorbing towers 5-(p-Hydroxyphenyl )-10,15,20-triphenylporphine 1.Yield in semiconductor factories. Given that the environmental 3.5%, purple crystals, mp>300 °C. Rf, 0.43 (DCM). standard for HCl gas is 5 ppm, in the present work, the optical UV–VIS(CHCl3) lmax/nm (e/dm3 mol-1 cm-1) 417 (490 000), properties of immobilized substituted tetraphenylporphines 514 (19 000), 549 (9300), 591 (5900), 645 (5400).dH (CDCl3) were examined for their potential use in the detection of such 8.80 (s, 8H, pyrrole b-H), 8.17 (m, 6H, aromatic H), 7.70 (m, levels of HCl gas. Furthermore, we also discuss the eVects of 7H, aromatic H), 7.23 (m, 4H, aromatic H). MS(FAB) m/z: substituents on sensitivity, response behavior and long term 631.2 (M+H+). stability. 5-(p-Hydroxyphenyl )-10,15,20-tris(p-tertbutylphenyl )porphine 2.Yield 2.9%, purple crystals, Experimental mp>300 °C. Rf, 0.47 (DCM). UV–VIS(CHCl3) lmax/nm Chemicals (e/dm3 mol-1 cm-1) 420 (570 000), 517 (20 000), 554 (12 000), 592 (5800), 649 (7100). dH (CDCl3) 8.85 (s, 8H, pyrrole b-H), Synthesis of 5-(p-hydroxyphenyl)-10,15,20-tris( p-alkylphe- 8.10 (m, 10H, aromatic H), 7.76 (m, 4H, aromatic H), 7.20 (m, nyl)porphine [TP(OH) (R)3PH2] 1–3. 2H, aromatic H), 1.60 (s, 27H, But). MS(FAB) m/z: 799.4 The general method was modified by Adler et al.9 as follows: (M+H+). Anal. calc. for C56H54N4O (798.4): C, 84.17; H, 6.82; p-hydroxybenzaldehyde (12 mmol), p-alkylbenzaldehyde or p- N, 7.02. Found: C, 84.21; H, 6.80; N, 7.01%. alkoxybenzaldehyde (36 mmol) in propionic acid (150 cm3) was stirred and slowly heated to 80 °C until the p-hydroxybenz- 5-(p-Hydroxyphenyl )-10,15,20-tris(paldehyde dissolved.Pyrrole (50 mmol) was slowly added to octyloxyphenyl )porphine 3. Yield 2.8%, purple crystals, the above solution and heated at 150 °C, then the reaction mp>300 °C. Rf, 0.52 (DCM). UV–VIS(CHCl3) lmax/nm mixture was refluxed for 70 min and allowed to cool overnight.(e/dm3 mol-1 cm-1) 423 (550 000), 515 (21 000), 555 (15 000), Ethanol (150 cm3) was added to the dark propionic acid 593 (6400), 651 (9700). dH (CDCl3) 8.90 (s, 8H, pyrrole b-H), residues under vigorous stirring at room temperature for 8.05 (d, 6H, aromatic H), 7.97 (m, 2H, aromatic H), 7.87 (m, 30 min, then the residue was filtered through a sintered funnel 6H, aromatic H), 7.50 (d, 6H, aromatic H) 7.08 (m, 8H, and washed with ethanol until the filtrate became clear.The aromatic H), 4.10 (t, 6H, MOMCH2M), 2.0 (m, 6H, MCH2M), violet solid obtained was dissolved in chloroform (150 cm3), 1.60–1.30 (br m, 30H, MCH2M), 0.90 (t, 9H, MCH3). washed with saturated aqueous sodium carbonate (3×50 cm3), MS(FAB) m/z: 1015.6 (M+H+). and dried over anhydrous sodium sulfate.After solvent evapor- Tetraphenylporphine (chlorin free) (TPPH2), and 5,10,15,20- ation, the purple needles obtained were chromatographed on tetrakis( p-hydroxyphenyl)porphine [TP(OH)PH2] were obalumina, and eluted with dichloromethane (DCM)–n-hexane tained from Aldrich Chemicals and Tokyo Kasei. The molecular structures of the porphines are shown. Ethylcellulose (EC) was obtained from Aldrich Chemicals.Porphines and *E-mail: sadaoka@en2.ehime-u.ac.jp J. Mater. Chem., 1998, 8(5), 1199–1204 1199HO 5-( p-hydroxyphenyl)-10,15,20-triphenylporphine [TP(OH)(H)3PH2] tetraphenylporphine (TPPH2) N NH N HN N NH N HN 5,10,15,20-tetrakis( p- tert-butylphenyl)porphine [TP(But)PH2] 5-( p-hydroxyphenyl)-10,15,20-tris( p- tert-butylphenyl)porphine [TP(OH)(But)3PH2] But N NH N HN But But But OH N NH N HN But But But 5,10,15,20-tetrakis( p-octyloxyphenyl)porphine [TP(OC)PH2] 5-( p-hydroxyphenyl)-10,15,20-tris( p-octyloxyphenyl)porphine [TP(OH)(OC)3PH2] C8H17O N NH N HN OC8H17 OC8H17 C8H17O HO N NH N HN OC8H17 OC8H17 C8H17O EC were dissolved in a mixture of toluene, ethanol and bis(2- channel spectrophotodetector (MCPD-1000, Otsuka electronics).The spectrum (I0) of the composite film was first ethylhexyl) phthalate (DOP) as a plasticizer. In the previous work,10 the absorption spectra of the EC-composite were measured in nitrogen and used as a reference for measuring the spectrum (I/I0) of the film in other environments. The examined for TPPH2 and TP(OH)PH2. The half width of the Soret band increases with porphine content indicating inter- reflectance (%) is defined as 100 I/I0.Standard dry gases (HCl, Cl2, NO2 and NO) diluted with nitrogen were obtained from molecular interactions, e.g. concentration dependent aggregations. A large proportion of the porphine results in formation Sumitomo Seika. The concentration was controlled by mixing the standard gas with nitrogen. of inhomogeneous films containing some porphine crystals.For the films containing 5×10-5 mol g-1 of EC or less, the half width of the band remains a constant, and smooth, homogeneous films are obtainable. To obtain reproducible Results and Discussion characteristics, the films on alumina and/or quartz substrates The absorption spectra in the UV–VIS region of free base from solutions of concentration 5×10-5 mol (g EC)-1 or less tetraphenylporphines have been extensively documented for were prepared with a spinner. The films were heated at 60 °C thin solid films and solutions.These spectra all consist of a in vacuo to remove the solvent. very strong band around 420 nm (the Soret band) and four moderately strong bands (Q-bands) in the 500–650 nm region. Optical measurements It is well known that in nonaqueous media the porphine macrocycle is oxidized in successive monoelectronic steps The spectra of the thin films (~5 mm) deposited on alumina plates were measured in reflection mode.Filtered light from a giving monocationic radicals and dications. Carnieri and Harriman11 have reported that radical p-cations are very D2/I2 lamp (400–800 nm, 15W) was guided into a fiber and the reflected light was collected and analyzed using a multi- unstable in solution, being oxidized to the p-dications by 1200 J.Mater. Chem., 1998, 8(5), 1199–1204Fig. 2 Spectral changes of TPPH2–EC composite without DOP upon Fig. 1 Absorption spectra of TPPH2-benzene solution with and withexposure to HCl gas at 30 °C. TPPH2: 5×10-5 mol per g EC. HCl out HCl concentrations in ppm are shown.electron loss. Furthermore, as reported in 1951 by Dorough et al.,12 the amphoteric nature of the porphine molecule permits the formation of acid salts involving the addition of protons to the center of the porphine and the optical absorption spectra of these salts are influenced by the nature of the acid. The porphine nucleus can be regarded structurally as a polyvalent amphotyte or ampholite because all four nitrogen atoms are potential basic centers and the two pyrrolic type (NNH) nitrogen atoms are possible acidic centers.Absorption spectra of TPPH2–benzene solutions (5×10-5 mol cm-3, 5cm 3 ) with and without conc. HCl, 2H+ N NH N HN N NH N HN H+ H+ HNO3 and HF solution (5×10-4 cm3) were measured. For Scheme 1 Protonation process the benzene solution, the Soret band is at 446 nm for HCl, 439 nm for HNO3 and 435 nm for HF.The result for HCl is shown in Fig. 1. From these spectra, one can note that the spectral pattern changed upon addition of HCl; the four Qband spectrum, indicating D2h symmetry for free-base porphine, changed to a two Q-band spectrum, indicating D4h symmetry. The change in the spectra upon addition of HCl can be attributed in general to the attachment of protons (diprotonation) to two imino nitrogen atoms of the pyrroline-like ring in the free-base.A similar spectral change is expected for the EC composite film. When dry HCl gas was introduced into the chamber, the spectral response to HCl concentration changes is as shown in Fig. 2 for the DOP free film containing 5×10-5 mol g-1 of EC of TPPH2.The reflectance at lmax=446 and 662 nm decreased and some isosbestic points were detected. These changes were reversible. These results are very similar to the changes observed upon diprotonation of TPPH2 (Scheme 1). Fig. 3 shows the percent reflectance changes of TPPH2–EC composite at lmax=446 nm during exposure to nitrogen and 12 ppm HCl. The response and recovery times became shorter with increase in working temperature, while the degree of the Fig. 3 Response behavior of TPPH2–EC composite film without DOP at 446 nm. HCl concentration is changed from 0 ppm (nitrogen) to changes/sensitivity became smaller. The doping with DOP was 12.7 ppm and the reflectance measured again. ($) 30°C, (&) 45°C eVective for improving the response behavior without aVecting and (+) 60°C.the lmax values. The response behavior was examined for a TPPH2–EC composite containing DOP. The doping resulted in an enhancement of the sensitivity at the Soret and Q(0–0)- band under near-UV–VIS (400–800 nm) continuous irradiation for TPPH2–EC composite containing DOP were band; both the response and recovery time became shorter, as shown in Fig. 4. For free-base tetraphenylporphine, the examined, confirming that the sensitivity was halved after 30 d as shown in Fig. 5. To improve long-term stability, the use of absorbance of the Soret and Q-bands was reversibly sensitive to ppm levels of HCl at room temperature. Some fading was near-UV-cut light was considered. Under irradiation with filtered light (>600 nm), a marked deterioration of the detected for specimens exposed to light from a 50 W xenon lamp for 3 h.Irradiation with light from a D2/I2 lamp (15W) sensitivity was not observed for more than 50 d. To maintain long-term stability, operation in a longer wave- resulted in some deterioration of the sensitivity, indicating a lack of long-term stability. The sensitivity changes of the Soret length region (>600 nm) is preferable while the molar absorp- J.Mater. Chem., 1998, 8(5), 1199–1204 1201Fig. 4 Reflectance changes at 448 nm ($) and 662 nm (#) of Fig. 6 Spectral changes of TP(OH) (H)3)PH2–EC composite upon TPPH2–EC composite film at 40 °C. TPPH2: 2.5×10-5 mol per g EC exposure to HCl gas at 30 °C. TP(OH) (H)3PH2: 5×10-5 mol g per with DOP HCl concentration is changed from 0 ppm (nitrogen) to EC.HCl concentrations in ppm are shown. 12.7 ppm and the reflectance measured again. work,10 the spectral changes with time of 5,10,15,20-tetrakis( phydroxyphenyl) porphine–EC composite upon exposure to 0.09 ppm of dry HCl gas were examined. Exposure to 0.09 ppm HCl resulted in a gradual decrease in the percent reflectance at about 455 and 710 nm with blue-shifts. The response time was extremely long compared to that for TPPH2–EC composites. The recovery time was also long, e.g.the specimen must be held in pure nitrogen for 3 d or more at room temperature to recover the initial state. The sensitivity of the Q(0–0) band was very high and reversible when the blueshifts were detected. The response behavior and the sensitivity may be influenced by the number of p-hydroxyphenyl groups, so we synthesized and examined substituted tetraphenylporphines.In dimethylformamide (DMF) solution, lmax of the Soretand Q(0–0)-bands of the neutral form are 416 and 647 nm for TPPH2, 418 and 649 nm for TP(OH) (H)3PH2, 422 and 653 nm for TP(OH) (H)3PH2, 419 and 651 nm for TP(But)PH2, 420 and 651 nm for TP(OH) (But)3PH2, 421 and 651 nm for Fig. 5 Change of the sensitivity to 10 ppm HCl of TPPH2–EC com- TP(OC)PH2, 422 and 651 nm for TP(OH)(OC)3PH2, respectposite with DOP at 30 °C.During the measurement, the composite ively. For the DMF solution with conc. HCl, lmax values of was exposed continuously to light. the Soret- and Q(0–0)-band of the dication form are 446 and 664 nm for TPPH2, 451 and 674 nm for TP(OH) (H)3PH2, 456 and 703 nm for TP(OH)PH2, 450 and 674 nm for tion coeYcient of the Q-band is about tenfold lower than that of the Soret band for the acid dication form of TPPH2. For TP(But)PH2, 453 and 683 nm for TP(OH) (But)3PH2, 456 and 694 nm for TP(OC)PH2, 456 and 697 nm for TPPH2–EC composites, introducing 0.1 ppm HCl resulted in a decrease of only about 2% in reflectance at 662 nm [Q(0–0) TP(OH)(OC)3PH2, respectively .The ratio of the absorbance of the Q(0–0)/Soret band for the dication form is 0.13 for band]. To improve sensitivity, the use of TPPH2 derivatives having a higher molar absorption coeYcient at the Q-band is TPPH2, 0.20 for TP(OH) (H)3PH2, 0.22 for TP(OH)PH2, 0.15 for TP(But)PH2, 0.21 for TP(OH) (But)3PH2, 0.20 for desirable.Acid dications showed an enhanced bathochromic shift relative to the meso-tetraphenylporphine itself. Thus the TP(OC)PH2, 0.21 for TP(OH)(OC)3PH2. The absorbance ratio for the mono p-OH substituted tetraphenylporphines for molar absorption coeYcient of the Q(0–0) band appeared in a longer wavelength region (>650 nm); the larger the shift, the the dication form is higher than that for the porphines without a p-OH group.10 larger the electron donating power of the substituents.Meot- Ner and Adler13 reported that an increase in the electron- Fig. 6 shows the spectral changes of the TP(OH) (H)3PH2– EC composite films without DOP. The introduction of one donating power of the para substituents results in a red shift of all the observed peaks for both free-base and dication forms p-OH group resulted in red shifts of both the Soret- and Q-bands.Moreover, lmax of Q(0–0) band of the dication with an increase in the oscillator strength. It seems that the oscillator strength increases monotonically with the lmax of form was shorter than that of the dication form of tetrakis( phydroxyphenyl) porphine. In ambient HCl, lmax values of peak I [Q(0–0) band] for both free-base and dicationic forms.These results suggested to us that the substitution of the Soret- and Q(0–0)-bands were 454 and 677 nm for TP(OH)- (But)3PH2, and 456 and 693 nm for TP(OH)(OC)3 hydrogen para to the phenyl group with an electron donating substituent, such as hydroxy, is suitable to improve and PH2, respectively.For the mono p-OH substituted tetraphenylporphines, the sensitivity to HCl gas of the Soret- and enhance sensitivity in the Q(0–0) band region. Furthermore, it is expected that the HCl sorption ability may be enhanced Q(0–0)-band was considerably higher than that of the unsubstituted tetraphenylporphine. It is confirmed that for the EC by the presence of the phenolic hydroxy group.In previous 1202 J. Mater. Chem., 1998, 8(5), 1199–1204composite films replacing the para-hydrogen in the phenyl The response behavior of TP(OH)(OC)3PH2 is shown in Fig. 9. While both response and recovery times of mono p-OH group with a hydroxy group would also be eVective in enhancing the absorbance of the Q(0–0) band of the dication form substituted tetraphenylporphines are considerably longer than that of tetraphenylporphine, the response behavior was revers- with red shifts, in which the degree of the red shifts increases with the number of p-OH groups. ible and became faster with increasing temperature.The response and recovery times of 5-( p-hydroxyphenyl)-10,15,20- The calibration curves at the Soret- and Q(0–0)-bands are shown in Fig. 7 and 8, respectively, for the composite films triphenylporphine composite were faster than those of the 5,10,15,20-tetrakis( p-hydroxyphenyl)porphyrin composite. without DOP. The sensitivity at both bands was in the following order: TPPH2<TP(OH) (But)3PH2<TP(OH)- When the working temperature was increased from 45 to 60 °C, the percent reflectance of the Soret-band at 12 ppm HCl (OC)3PH2TP(OH) (H)3PH2.This trend can be ascribed to the electron donating power of the para substituents. The ratio changed from 86 to 94 for TPPH2 and remained the same (78) for TP(OH)(OC)3PH2. The introduction of a single p-OH of log(I0/I) at the Q(0–0) band and log(I0/I) at the Soret band upon exposure to 12.7 ppm HCl was evaluated to be group resulted in a decrease in the temperature coeYcient of the sensitivity for both the Soret- and Q(0–0)-bands, as shown 0.88, 0.85, 0.69, 0.68, 0.40 and 0.35 for TP(OH)(OC)3PH2, TP(OH) (H)3PH2, TP(OH) (But)3PH2, TP(OC)PH2, TPPH2 in Fig. 9. Significant deterioration of the sensitivity under irradiation with filtered light (>600 nm) was not observed for and TP(But)PH2, respectively. The introduction of one p-OH resulted in the enhancement of the HCl sensitivity at the more than 50 d for the 5-( p-hydroxyphenyl)-10,15,20-tris( p-Rsubstituted- phenyl)porphine composite films without DOP.Q(0–0)-band. It is interesting to note that at the Q(0–0) band, the sensitivity of the composite films with tetraphenylporphine Furthermore, tests in other gaseous environments showed that the Soret- and Q-bands of the films were also sensitive to substituted with a single p-OH group was higher than that of TPPH2-composite films doped with DOP (as mentioned the vapors from aqueous solution of HNO3, HF or HCOOH, while for a benzene solution, the Soret and Q-bands were HCl sensitivity of TPPH2 composite film was enhanced by the addition of DOP).insensitive to HCOOH which may be related to the water content.Furthermore, they were mostly insensitive to vapors from CH3COOH or C2H5COOH. To clarify the reasons for these observed diVerences in the sensitivity (selectivity), we needed to measure the sorption characteristics of the composite films, since the sensitivity is influenced by the sorption ability and solubility of the composite film for these organic acids and water.In dry conditions, the sensitivity to HCl gas was not influenced by the coexistence of 2000 ppm of H2 and CO2. The percent reflectance at the Soret band (lmax=440 nm) decreased by only 1% for 8 ppm NO2 and 0.5% or less for 10 ppm NO. The changes for NOx may be attributed to the formation of HNO3 by the reaction with water as a contaminant. It is expected that the sorption of NO2 results in the formation of a radical p-cation or p-dication; the p-cations are very unstable in solution, being oxidized to p-dications as reported by Carnieri and Harriman.11 The p-dications are also reactive and react to give the acid dication by protonation.The lack of observation of spectral changes indicating the formation of radical p-cation or p-dication may be related to the diVerence in permeability of the EC composite for HNO3 and NOx and/or the diVerence in stability of acid dications Fig. 7 HCl concentration dependence of log(I0/I) at the Soret band at and radical cations in the EC matrix. The percent reflectance 30 °C. Porphine concentration: 5×10-5 mol per g EC; (#) TPPH2, ($) at the Soret band decreased by only 0.5% for 1 ppm Cl2 while TP(OH) (H)3PH2, (&) TP(OH) (But)3PH2, (+) TP(OH)(OC)3PH2.Fig. 9 Reflectance changes of TP(OH)(OC)3PH2–EC composite at Fig. 8 HCl concentration dependence of log(I0/I) at the Q(I)-band at (-- --) 45 and (—) 60 °C; and (#) 693 nm, ($) 456 nm. HCl concentration is changed from 0 ppm (nitrogen) to 12.7 ppm and the reflec- 30 °C; (#) TPPH2, ($) TP(OH) (H)3PH2, (%) TP(Bu t )PH2, (&) TP(OH) (But)3PH2, (6) TP(OC)PH2, (+) TP(OH)(OC)3PH2.tance measured again. J. Mater. Chem., 1998, 8(5), 1199–1204 1203the presence of a large excess of Cl2 (5 ppm) resulted in a of HCl gas, 5 ppm being the environmental standard for HCl gas. decrease of 10% and only partial recovery was observed when the introduction of Cl2 gas was stopped. It is well known that Cl2 interacts with water and forms HCl and HClO.HClO is References an unstable compound and decomposes to HCl and O2, especially under light irradiation. If Cl2 is changed completely 1 H. E. Posch and O. S. Wolfbeis, Sensors Actuators, 1988, 15, 77. 2 Q. Zhou, D. Kritz, L. Bonnell and G. Siger, Jr., Appl. Optics, 1989, to HCl, a reversible response behavior is expected. A lack of 28, 2022. reversibility to Cl2 may be due to some other side reactions 3 R.Gvishi and R. Reisfeld, Chem. Phys. L ett., 1989, 156, 181. with the porphine, such as chlorination. In any case, a more 4 O. S. Wolfbeis, Fiber Optic Chemical Sensors and Biosensors II, detailed discussion about cross-sensitivity requires other CRC Press, Inc., Boca Raton, USA, 1991. results. 5 K. Wang, K. Seiler, J.P. Haug, B. Lehmann, S. West, K. Kartman and W. Simon, Anal. Chem., 1991, 63, 970. 6 Y. Sadaoka, Y. Sakai and Y. Murata, T alanta, 1992 39, 1675. Conclusions 7 Y. Sadaoka, Y. Sakai and M. Yamada, J. Mater. Chem., 1993, 3, 877. Spectral changes of tetraphenylporphine and its derivatives 8 Y. Sadaoka, Y. Sakai and M. Yamada, Denki Kagaku, 1994, 62, dispersed in ethylcellulose were examined for detection of sub- 1066. ppm levels of HCl gas. The sensitivity in the Q(0–0) band 9 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour and L. KorsakoV, J. Org. Chem., 1967, 32, 476. region is enhanced by replacing the hydrogen para to the 10 K. Tanaka, C. Igarashi, P. Tagliatesta, T. Boschi and Y. Sadaoka, phenyl group with electron donating substituents, while the J.Mater. Chem., 1996, 6, 953. response time is prolonged. Marked deterioration of the sensi- 11 N. Carnieri and A. Harriman, Inorg. Chim. Acta., 1982, 62, 103. tivity under irradiation with filtered light (>600 nm) was not 12 G. D. Dorough, J. R. Millaer and F. M. Huennekens, J. Am. Chem. observed for more than 50 days, for the composite films Soc., 1951, 73, 4315. examined. An HCl gas sensor based on mono-substituted 13 M. Meot-Ner and A. D. Adler, J. Am. Chem. Soc., 1975, 97, 5107. tetraphenylporphine with a p-OH in one phenyl group shows superior performance for detection of emissions of ppm levels Paper 7/08482J; Received 24th November, 1997 1204 J. Mater. Chem., 1998, 8(5), 1199–1204

ISSN:0959-9428    

DOI:10.1039/a708482j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Thickness control and defects in oriented mesoporous silica films Hong Yang, Neil Coombs and GeoVrey A. Ozin* Materials Chemistry Research Group, L ash Miller Chemical L aboratories, University of T oronto, 80 St. George Street, T oronto, Ontario, Canada, M5S 3H6 By using a surfactant-based synthesis strategy, we have earlier demonstrated that the polymerization and growth of silicate micellar assemblies at the air–water interface, under quiescent and dilute acidic aqueous conditions, yields free-standing submicron thickness hexagonal mesoporous silica films in which the channels are oriented parallel to the film surface.TEM imaging studies of these thin films showed that microscopic defects pervade the channel structure with topologies resembling those found in lyotropic liquid crystals.This suggested that the mesoporous silica film evolved from silicification of a surface lyotropic silicate mesophase. Herein it is demonstrated that film growth, defect structure, extent of polymerization, and mesoporosity sensitively depend on the choice of synthesis acidity, temperature and mixing, and in the case of supported films, on the choice of substrate.In particular, a ten-fold increase in the thickness of the film can be obtained by simply lowering the acidity and moving to ambient temperature conditions whilst an alteration in mixing conditions can change the film from a discrete to a continuous morphology. Combined PXRD, TEM and nitrogen adsorption studies show that the silica films are hexagonal, oriented and mesoporous.Furthermore, the observation of a focal conic fan-type texture in the free-standing films shows that defect controlled director fields, that exist in a precursor hexagonal lyotropic silicate mesophase, are preserved in the channel structure of the mesoporous silica phase. Proof-of-existence of liquid crystalline texture in such free-standing mesoporous silica films, provides direct evidence that film growth evolves from the cooperative assembly and organization of silicate micellar species at the air–water interface.templating strategies have been successfully used to synthesize Introduction mesostructured materials, the formation pathways are not Liquid crystals represent a delicate phase of matter which has necessarily the same.4,5,8,16–22 In the concentrated surfactant lost long range positional order of ordinary crystals but retains regime, the formation of mesostructured materials likely proorientational order of anisotropic structural units.1–3 Defects ceeds through the mineralization of a pre-existing liquid crystal in liquid crystals, unlike their atomic scale counterparts in mesophase.21 By contrast, in the dilute regime, the mesostrucnormal crystals, are microscopic in size, their formation ture likely forms by mineralization of a co-assembly of silicate requires much less energy, and their topology determines the micellar templates.4,5,16–18 In this study, proof-of-existence of patterns of director fields.They are responsible for birefrin- hexagonal liquid crystalline texture in free-standing mesogence textures made visible between cross polarizers in an porous silica films that are grown at the boundary between optical microscope where distinct patterns are diagnostic of air and water under very dilute aqueous conditions, provides particular liquid crystal structure types.2,3 evidence that film growth occurs through the cooperative In this context, it has recently been demonstrated that the assembly pathway.polymerization of silicate micellar assemblies4,5 at the air– water interface, under dilute and acidic aqueous conditions, yields free-standing hexagonal mesoporous silica films with a Experimental thickness of ca. 0.5 mm, in which the channels are oriented parallel to the film surface.6–9 Free-standing hexagonal meso- Synthesis porous silica films with a diVerent space group, P63/mmc, were The film synthesis procedure involved a modified version of subsequently reported.10 Herring bone, U-shaped and S-shaped that reported earlier for the preparation of mesoporous silica channel designs have been observed by TEM in these hexagmorphologies. 7,15 Tetraethylorthosilicate (TEOS, 99.999+%, onal mesoporous thin film samples.7 Their channel architec- Aldrich), cetyltrimethylammonium chloride (CTACl, 29 wt.% ture6–8 displayed a close resemblance to the director field aqueous solution, Pflatz & Bauer) and hydrochloric acid patterns in hexagonal organic liquid crystals that are usually (36.5–38 wt.% aqueous solution, BDH) were used as received. associated with common line defects,11–13 such as +p, -p The reactant ratios used for making the film with a thickness disclinations, pairs of +p disclinations, edge dislocations, of ca. 5–10 mm were 100 H2O51.0 HCl50.11 CTACl50.13 bending and wall defects.14 TEOS. In a standard preparation, 2.9 g of a CTACl surfactant In this article we show that by simply employing less acidic aqueous solution (29 wt.%) was mixed well with 2.5 g of HCl synthesis conditions than those in our earlier study, it is solution (36.5–38%) and 40.8 g of deionized water by using a possible to realize at least a ten-fold increase in the thickness magnetic stirrer (Corning PC-351 hot plate stirrer) with a of the mesoporous silica films, while mixing conditions can 0.375 in×1.5 in stir bar in a polypropylene beaker followed by also aVect the morphology of the films.Polarizing optical adding 0.65 g of TEOS. The mixture was then stirred for 3 to microscopy shows that these thick films display a fan-type 10 min at room temperature. The final mixture was transferred texture diagnostic of a hexagonal lyotropic organic liquid into either a round or a square polypropylene (PP) or low crystal, HI phase.Significantly, the texture is maintained on density polyethylene (LDPE) bottle with diVerent diameters removing the surfactant and after thermally annealing the and length of edge (NalgeneA, LABCOR, Inc.), and allowed films. This implies that the optical birefringence emerges from to achieve a quiescent state. The mesoporous silica growth the polarization response of electron density circumscribing a process was typically allowed to proceed for a period of one hexagonal array of mesoscale glassy channels, that is, ‘mesosweek under static conditions at room temperature.Depending cale optical anisotropy in glass’.15 It is worth mentioning that while diVerent surfactant-based on the initial time period and the stirring rate for the mixing, J.Mater. Chem., 1998, 8(5), 1205–1211 1205diVerent optical birefringence textures were observed. The film on mica was grown by allowing a freshly cleaved muscovite mica substrate (J. B. EM. Services Inc., Dorval, Quebec) to float on the solution surface. The calcination of the film was achieved using two diVerent procedures. Direct calcination was done in air and in a furnace attached to an Omega CN- 2010 programmable temperature controller.The temperature ramp was less than 1 °C min-1 and typically the sample was held at 450 °C for 4–10 hours. The other calcination method involved two steps, the sample was first dehydrated at 150 °C for over 10 hours under 10-5 Torr dynamic vacuum and then heated in air at 450 °C for ca. 10 hours. Most of the characterization work for the as-synthesized and calcined film samples was done with those having a fan type texture and using the direct calcination procedure unless mentioned otherwise. Characterization Powder X-ray diVraction (PXRD) data were obtained on a Siemens D 5000 diVractometer using Ni-filtered Cu-Ka radiation with l=1.54178 A ° .Home made quartz low background sample holders and plexiglass sample holders were used for mounting the intact films or ground films, and for recording the PXRD patterns.Scanning electron microscopy (SEM) images were obtained on a Hitachi S-4500 field emission microscope using a low acceleration voltage of 2 kV to minimize the charging of the mesoporous silica surfaces. Samples were uncoated and imaged directly. Transmission electron microscopy (TEM) images were recorded on a Philips 430 microscope operating at an accelerating voltage of 100 kV with a typical recording magnification in the range 80 000 to 160 000 times.The microscope has a working resolution of 3.5 A ° . In order to get ultrathin (ca. 400–600 A ° ) sections of the mesoporous silica morphologies, the samples were embedded in epoxy resin and sectioned using an RMC MT6000 ultrami- Fig. 1 Representative SEM images of an as-synthesized mesoporous crotome in combination with a Drukker diamond knife follow- silica film formed at the air–water interface showing (A) a typical surface with bending, and (B) cross section with a thickness of ing the standard procedure. Embedding in Spurr’s epoxy resin ca. 5–10 mm (TAAB laboratories equipment, Aldermaston, UK) was used for calcined film samples and a cyanoacrylate resin (SuperglueA) for as-synthesized film samples.Additional hardshows the thickness to be ca. 5–10 mm thick, Fig. 1(B). The ening of the embedding matrix was induced at 60 °C for 12 thickness of the film that grows at the air–water interface hours. Polarized optical microscopy (POM) images were depends on the conditions of the solution phase. Representative obtained on a BH-2 Olympus optical microscope with a POM images obtained between crossed polarizers, for meso- Kodak Gold Ultra 400 film. Proton-decoupled 29Si solid state porous silica films formed under slightly diVerent conditions magic angle spinning nuclear magnetic resonance (MAS NMR) are shown in Fig. 2. In contrast to the previously reported spectra were recorded on a Bruker DSX 200 MHz spectrometer images for ca. 0.5 mm mesoporous silica thin films,6 the at 40 MHz using a 90° pulse with a delay time of 600 seconds. newly obtained thick films display classic liquid crystal textures. Computer simulation of the NMR spectra employed a Bruker The transformation of the films from ones displaying discrete deconvolution program.Thermal analysis (DSC and TGA) birefringent patterns, Fig. 2(A), to ones with fan-type textures, data were recorded on Perkin-Elmer Thermal Analysis Series Fig. 2(B), can be controlled by simply choosing the stirring 7 instrumentation under N2. The temperature ramp was at time or rate of the synthesis mixture before it is set into a 5 °C min-1. The surface area and mesoporosity of the film quiescent growth state.The films that have a fan-type texture were obtained on a McBain balance. Details of the set-up and were obtained for the mixture with a stirring time of about 10 measurement procedure have been published elsewhere.23 To minutes at low stirring rate, Fig. 2(B), or about 5 minutes at prepare a sample for the measurement of adsorption isotherms, high stirring rate, while the ones showing discrete birefringence a suYcient quantity of the as-synthesized films was first ground patterns emerged after a stirring period of 3 to 5 minutes at to a fine powder and then calcined following either one of the low stirring rate, Fig. 2(A). The observed fan-type texture is calcination procedures mentioned above. typical of a hexagonal lyotropic liquid crystal HI phase having the optical axis in the plane of the film.2,3 The fan-type texture Results is essentially invariant on removing the surfactant and after annealing the film at 450 °C, Fig. 2(C). This implies that the An optical microscopy image of a free-standing film obtained optical birefringence of the film does not require the surfactant in a synthesis that employed an agitation time of 10 minutes to be present in the channels and that strain anisotropy in the shows that the film is optically transparent.Scanning electron film is not the source of the fan-type texture. The study microscopy (SEM) images of the film are shown in Fig. 1. The herewith was conducted with samples that have fan-type film is continuous and the surface of the film that grows textures obtained for the mixture with a stirring time of about adjacent to the air interface has a smoother surface than that 10 minutes, at low stirring rate of the synthesis mixture before of the growing front emerging at the water interface, Fig. 1(A). it is set into a quiescent growth state, unless stated otherwise. The observed bending of the film presumably arises from a stress induced drying eVect.A cross-sectional view of the film Powder X-ray diVraction (PXRD) traces of these meso- 1206 J. Mater. Chem., 1998, 8(5), 1205–1211Fig. 3 PXRD traces of as synthesized mesoporous silica films, (a) without and (b) with grinding; calcined mesoporous silica films, (c) without and (d) with grinding Fig. 4 PXRD traces of (a) calcined ground film without dehydration and (b) calcined ground mesoporous silica films after dehydration treatment the oriented mesoporous films was investigated further by examining the eVect of grinding.The ground-up film samples are white powders. The PXRD trace for the ground sample, Fig. 3( b), showed the expected four peaks (100), (110), (200), (210) from diVraction planes that are typically seen in randomly oriented powder preparations of hexagonal mesoporous silica.4,5 The calcined and annealed ground-up samples, Fig. 3(d), also show a large contraction of the d100-spacing similar to that for the calcined oriented film, Fig. 3(c). It is observed that after the vacuum dehydration treatment at Fig. 2 POM images of mesoporous silica films under cross polarizers: 150 °C, the d100 diVraction peak contracts ca. 2A ° , and then (A) discrete texture of an as-synthesized film; fan-type texture of (B) an as-synthesized and (C) a calcined film (scale bar: 50 mm) further calcination of the dehydrated sample leads to a more well ordered mesoporous silica structure than that obtained without the vacuum pre-treatment. This is evidenced by a higher diVraction intensity and a greater number of reflections porous silica films are shown in Fig. 3. The PXRD pattern of as-synthesized and calcined film confirm them to be hexagonal in the PXRD patterns of the pretreated samples, Fig. 4. Clearly the moisture content of an as-synthesized incompletely poly- mesoporous silica and not the silicate liquid crystal mesophase for which the d100 appears at much lower angles,17 Fig. 3. The merized mesoporous film can aVect the stability of the structure.24 presence of only (100, 200) low angle reflections, Fig. 3(a), implies that the channels preferentially run parallel to the The orientation of the channels for the as-synthesized and calcined hexagonal mesoporous films is confirmed by TEM surface of the film.6 This structure is retained after surfactant removal by calcination and is accompanied by contraction of images of microtomed thin sections, Fig. 5. The expected hexagonal honeycomb structure is seen in both as-synthesized the hexagonal mesostructure due to condensation–polymerization of residual hydroxyls in the silica channel walls.4 The and calcined mesoporous silica films. Careful inspection of the TEM images shows that the hexagonally packed pores are not relatively large contraction of the d100 spacing for the calcined film, Fig. 3(c), implies a much lower degree of polymerization as well organized as those in the thinner version of the film made at 80 °C. It is unlikely that such a diVerence is simply of the silica in the surfactant-containing precursor film relative to a higher acidity synthesis (see below).6–9 The structure of from the variation of imaging conditions. Note that a lower J.Mater. Chem., 1998, 8(5), 1205–1211 1207Fig. 5 Representative TEM images of mesoporous silica films: (a) as-synthesized, (b) calcined (no dehydration treatment), (c) calcined (with dehydration treatment) degree of condensation–polymerization of silica (see below) may lead to a less stable channel wall structure for the embedding and microtoming procedure.As far as we can judge from the TEM images, the order of the mesopores on the top (air interface) and bottom (water interface) faces of the films is about the same. Vacuum dehydration prior to calcination seems to be an essential step for stablizing a well ordered hexagonal mesoporous structure.Calcination without vacuum dehydration appears to cause a greater distortion of the hexagonal mesoporous structure, Fig. 5(b). Thermogravimetric analysis (TGA) of the as-synthesized film shows the expected weight changes corresponding to loss of imbibed water below 100 °C, surfactant template around 270 °C, and water from condensation of framework hydroxyls around 360 °C and 600 °C, Fig. 6. The total weight decrease is ca. 60–70% which represents a high-end loss for a hexagonal Fig. 6 A representative TGA trace of a mesoporous silica film mesoporous silica preparation. This is presumably because of the lower degree of polymerization and larger amount of surfactant template imbibed within the channels. combined results of the TGA and DSC show that the thermal properties of these mesoporous silica films closely resemble DiVerential scanning calorimetry (DSC) shows no evidence of an endotherm that can be ascribed to a liquid crystal or those of the powdered solid.Moreover, the imbibed surfactant within the channels is not behaving like a liquid crystal isotropic liquid melting transition of the encapsulated surfactant for a heating cycle between 20 °C and 250 °C, Fig. 7. The mesophase. 1208 J. Mater. Chem., 1998, 8(5), 1205–1211Fig. 7 A representative DSC trace of an as-synthesized mesoporous silica film with a heating cycle up to 250 °C Fig. 9 Nitrogen isotherms of free-standing oriented mesoporous silica films: (a) sample after dehydration at 150 °C, (b) sample calcined without dehydration pre-treatment, and (c) sample calcined with The proton-decoupled 29Si MAS NMR spectrum and comdehydration pre-treatment.All samples were ground into a powder puter deconvolution of the spectrum for the as-synthesized before the adsorption measurements mesoporous silica film are shown in Fig. 8. Three silicon sites are observed with a Q2[SiO2(OH)2]5Q3[SiO3(OH)]5 Q4(SiO4) ratio of 8542548. The observation of Q2 silicon shows both low and high pressure hysteresis.It is well docuspecies and the high value of Q2+Q3 relative to Q4 are mented that particular shapes of hysteresis loops can be consistent with the observed large contraction of the hexagonal associated with specific pore structures.25a Low pressure hystermesostructure on calcination (PXRD). This implies a lower esis in this case may be associated with distortion swelling of degree of silicate polymerization in the as-synthesized thick the walls of a partially condensed mesoporous silica films compared to the thin ones, as well as the usual meso- accompanying adsorption.25a The isotherm for the directly porous powders.calcined sample shows a lower uptake of nitrogen, has a much Quantification of the mesoporosity and surface area of the shallower inflection due to capillary condensation, and also film was conducted on a McBain balance.23 N2 isotherms at displays low and high pressure hysteresis.The BET surface liquid nitrogen temperature are shown in Fig. 9. The as- area is calculated to be ca. 750 m2 g-1. These observations synthesized silica films show negligible N2 adsorption after together with those from PXRD, TEM and NMR suggest that dehydration at 150 °C in vacuum implying that this treatment the vacuum-dehydration pre-treatment prior to calcination does not create void space for adsorbing N2.The isotherm for substantially improves the degree of order and mesoporosity the vacuum dehydrated–calcined sample is typical of that of the silica films.expected for Type IV demonstrating that the sample is meso- The thick mesoporous silica films can also be grown on a porous.25 The BET surface area is calculated to be ca. 1000 m2 variety of substrates, such as glass slides and tubes, and freshly g-1. The mean pore diameter estimated by the Dollimore–Heal cleaved muscovite mica. For the preparation of these films, the method from the adsorption branch of the isotherm is ca. 10 minute mixing period described above was used. Between 2.8 nm, which is consistent with the center-to-center distance crossed polarizers in the optical microscope, discrete birefrinof ca. 3.7 nm obtained from PXRD of calcined mesoporous gence patterns were observed for the films grown on planar film samples. Note that the desorption branch of the isotherm and curved glass substrates.The discrete patterns on glass appear to arise from the local nucleation and growth of silicatesurfactant assemblies with contributions from +2p disclination12 –14 concentric-type topological defects. Similar POM patterns have been observed for mesoporous silica discoid shapes that concurrently form in the bulk synthesis mixture.15 Interesting birefringence patterns were observed for the thick Fig. 8 The proton-decoupled 29Si MAS NMR spectrum and computer Fig. 10 A representative POM image of an as-synthesized mesoporous deconvolution of the spectrum for the as-synthesized mesoporous silica film silica film on mica (image size is 150×120 mm) J. Mater. Chem., 1998, 8(5), 1205–1211 1209films grown on freshly cleaved muscovite mica, Fig. 10. Light synthesized mesoporous silica films show no thermal events that can be associated with crystal–liquid crystal or isotropic coloured, grey and dark areas were observed for the thick films between crossed polarizers. melting transitions of an imbibed surfactant liquid crystal up to 250 °C, Fig. 6. Also, the fan-type texture is retained essen- Careful inspection of these images showed that striations on the patches with the same brightness align parallel on the film tially invariant on removing the surfactant and after annealing the film at 450 °C, Fig. 2(C). Therefore the optical birefringence surface and that the lines on patches with diVering brightness meet at 60° or 120° angles. Recall that oriented mesoporous of the film does not require the surfactant to be present in the channels.Furthermore, strain anisotropy in the film is not the silica films have been reported to grow on this surface.26 Thus the observed correlation of striations amongst similarly col- source of the fan-type texture. Finally, the PXRD and 29Si MAS NMR data show that the silica walls of the channels are oured domains, Fig. 10, presumably originates from preferential alignment of the channels in the mesoporous silica film glassy.One may safely conclude that the birefringence is associated with the optically uniaxial nature of the oriented along the hexagonal a,b-axes of the mica surface. hexagonal mesoporous silica film. The thick mesoporous silica films display two dominant Discussion morphologies which give rise to distinct POM birefringence patterns.The free-standing films synthesized with a stirring Quiescent, acidic and aqueous conditions are the key and essential prerequisites for our surfactant-templated synthesis period of 3 to 5 minutes at low stirring rate, Fig. 2(A), have a structure based upon discrete morphologies which appear to of hexagonal mesoporous silica films at the boundary between air and water.6,7 Under high acidity and 80 °C reaction con- have coalesced and show concentric birefringence patterns.Such morphologies have previously been observed for meso- ditions the films grow to a limiting thickness of about 0.5 mm. TEM images of the films show that while the channels are porous silica films grown on gold31 and glass32 surfaces. Similar morphologies can be found in bulk preparations that yield well organized in the plane of the film, they swirl and curl throughout the body of the film to create designs7,8 that discoid shape mesoporous silica where the channels run concentrically and coaxially around the main rotation axis of the resemble the patterns of director fields induced by topological defects such as +p, -p and +2p disclinations found in a discoid.33 These discrete types of POM patterns presumably arise from +2p disclinations with the rotation axes normal to discotic hexagonal liquid crystal mesophase.12,13 Studies of the early stages of film growth suggest that the the director field.Defect textures of this genre may reflect the seeds that spontaneously emerge in a lyotropic discotic hexag- process begins with the assembly of silicate liquid crystal seeds located at the air–water interface and templated by a surfactant onal phase and originate from vertical disclinations.13 Mesoporous silica films of this type tend to have domain overstructure.6,7,27–30 They silicify and expand in size through the accretion of silicate micelles and coalesce to form a structures and varied thickness.By contrast, free-standing films with a continuous and fan-type texture were obtained from a continuous film. Concurrent with film growth in two dimensions, mesoporous silica morphologies with well defined three synthesis mixture with a stirring time of about 10 minutes at low stirring rate, Fig. 2(B). The film shows good homogeneity dimensional shapes are evolving in the bulk aqueous phase.The reactant ratios, temperature and acidity of the synthesis and a smoother surface compared to those formed with less of a mixing period. Films with continuous and fan-type texture are important factors for controlling the curvature and size of these morphologies.15 In particular, it was found that less can also be obtained from a synthesis mixture with a stirring time of about 5 minutes at high stirring rate.The fan textures, acidic and room temperature conditions promoted the growth of well formed morphologies with dimensions as large as ca. however, did not transform into discrete textures on changing the vessel geometry, such as its shape and size. Thus, the 70 mm. With this knowledge of size and shape control of mesoporous silica morphologies, it has now proven possible diVerence in the POM birefingence patterns and surface morphologies might be best viewed as arising from a ‘switch’ in to gain command over the thickness and channel texture of mesoporous silica films grown at the air–water interface.the mode of formation of the free-standing film from one initiated by silicate liquid crystal seeds at the air–water The converging evidence from PXRD, TEM, and nitrogen isotherm measurements for thick mesoporous silica films shows interface, involving local growth and coalescence, to one involving the formation of a continuous silicate liquid crystal that they have oriented and hexagonally close-packed mesopores with the channel c-axis aligned parallel to the growth surface film.In both instances, silicification captures the defect structure and pattern of director fields in the precursor silicate interface. The as-synthesized and calcined films showed only (100) and (200) diVraction peaks, while additional (110) and mesophase, which is manifest in the channel design of the resulting mesoporous silica film. Boundary walls between the (210) diVraction peaks can be observed for the ground samples, Fig. 3. This establishes that the mesoporous silica films are defect domain structures are visible in the POM images. Notwithstanding this, the birefringence textures observed for hexagonal and oriented with the channels parallel to the growth surface. TEM images of these films also define the both kinds of free-standing mesoporous silica films show that the channel architecture is a silicified replica of the defect hexagonal mesopore arrangement and orientation of the channels for as-synthesized and calcined samples.The order of the induced pattern of director fields in a silicate liquid crystal precursor. It is also noteworthy that the texture traverses the mesopores in the front and back surfaces of the film are comparable. Although the film mesostructure was maintained entire extent of the film implying that the mesoporosity is not confined to small domains.in all the preparations of this study, the lower degree of polymerization–condensation of the silica in the thick films It is pertinent to inquire into the relation between the optical birefringence patterns of mesoporous silica films comprised of that are formed at lower acidity, evidenced by the larger (Q2+Q3)/Q4 ratio, may be the cause of the lower thermal discrete ribbon and discoid morphologies and those with fantype textures.Recall that the channels that run down the stability compared to the thin films formed at higher acidity. Consistent with this proposal is the observed large contraction length of the ribbon are found to whirl around the unique rotation axis of the discoids.8,15 When these discrete morpho- of the diameter of the mesopores for the calcined film samples. Thermal vacuum dehydration prior to calcination helps stabil- logies are viewed orthogonal to the channel director, optical extinction is found to occur only when the channel axis ize the mesostructure, Fig. 4. Although the formation of mesoporous silica films involves coincides with the optic axes of the polarizer or analyzer. In the case of the discoids, a roughly symmetrical black cross silicification of a lyotropic liquid crystal, the observed POM texture of the film does not arise from organized surfactant (the isogyre) emerges from a +2p disclination defect, while for the ribbon-shaped morphologies, a +p disclination defect assemblies in the channels.To amplify, the DSC trace of as- 1210 J. Mater. Chem., 1998, 8(5), 1205–12113 N. H. Hartshorne, T he Microscopy of L iquid Crystals, Microscope leads to the observed textures. The observed birefringence Publications Ltd., London, 1974, pp. 104–138. patterns are therefore optical manifestations of the diVerences 4 (a) C.T. Kresge, M. Leonowicz, W. J. Roth, J. C. Vartuli and in the channel structures of the mesoporous silica films that J. C. Beck, Nature (L ondon), 1992, 359, 710; (b) J. S. Beck, are prepared by stirring the synthesis mixture for diVerent J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, times prior to film growth in the quiescent state. As the stirring K.D. Schmitt, C. T.-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. time or rate and presumably the homogeneity of the synthesis Soc., 1992, 114, 10 834. mixture are increased, the discrete birefringence pattern of the 5 Q. Huo, D. I. Margolese, U. Clesia, P. Feng, T. E. Gler, P. Sieger, films so formed gradually merge into ones displaying the R.Leon, P. M. PetroV, F. Schu� th and G. D. Stucky, Nature continuous fan-type texture. This behavior might be thought (L ondon), 1994, 368, 317. as a ‘switch’ in the mode of formation of the films at the air– 6 H. Yang, N. Coombs, I. Sokolov and G. A. Ozin, Nature (L ondon), water interface, from one primarily involving the polymeriz- 1996, 381, 589. 7 H. Yang, N.Coombs, O� . Dag, I. Sokolov and G. A. Ozin, J.Mater. ation, growth and coalescence of a population of silicate liquid Chem., 1997, 7, 1755. seeds to one based on the polymerization and thickening of a 8 N. Coombs, D. Khushalani, G. A. Ozin, S. Oliver, G. C. Shen, continuous silicate liquid crystal film. I. Sokolov and H. Yang, J. Chem. Soc., Dalton T rans., 1997, 3941. The liquid crystal POM patterns and surface morphologies 9 (a) I.A. Aksay, M. Trau, S. Manne, I. Honma, N. Yao, L. Zhou, not only depend on the synthesis conditions, they also change P. Fenter, P. M. Eisenberger and S. M. Gruner, Science, 1996, 273, with the substrate properties. This can be seen from POM 892; (b) A. S. Brown, S. A. Holt, T. Dam, M. Trau and J. W. White, L angmuir, 1997, 13, 6363.images for films grown on amorphous surfaces, such as glass 10 S. H. Tolbert, T. E. Scha�Ver, J. Feng, P. K. Hansma and plates or tubes and the atomically flat mica surface. It is G. D. Stucky, Chem.Mater., 1997, 9, 1962. interesting to note that the POM patterns for the films grown 11 J. Feng, Q. Huo, P. M. PetroV and G. D. Stucky, Appl. Phys. L ett., on mica diVer from those on the other surfaces or subphases. 1997, 71, 620. Discrete and fan-type textures are replaced by extensive areas 12 Y. Bouligand, J. Phys., 1980, 41, 1297. of dark, grey and light patches, Fig. 10. The patterns of parallel 13 Y. Bouligand, J. Phys., 1980, 41, 1307. 14 M. Kle�man, Points, L ines and Walls: In L iquid Crystals, Magnetic striations within the diVerent patches of the mesoporous silica Systems and Various Ordered Media, John Wiley & Sons Ltd., t at angles of 60 or 120°.This observation suggests Chichester, 1983. that growth of the hexagonal mesoporous silica film occurs 15 H. Yang, N. Coombs and G. A. Ozin, Nature (L ondon), 1997, with the channel axis preferentially aligned along the hexagonal 386, 692. a,b-axes of the mica (001) surface. 16 A.Monnier, F. Schuth, Q. Huo, D. Kumar, D. Margolese, Finally, the observation of liquid crystal textures in meso- R. S. Maxwell, G. D. Stucky, M. Krishnamurty, P. PetroV, A. Firouzi, M. Janicke and B. F. Chmelka, Science, 1993, 261, 1299. porous silica films grown at the air–water interface under 17 (a) A. Firouzi, F. Atef, A. G. Oertli, G. D. Stucky and dilute aqueous and acidic conditions provides direct evidence B.F. Chmelka, J. Am. Chem. Soc., 1997, 119, 3596; (b) A. Firouzi, for a templating pathway based upon cooperative assembly D. Kumar, L. M. Bull, T. Sieger, Q. Huo, S. A. Walker, and organization of silicate micellar species4,5,16–18 rather than J. A. Zasadzinski, C. Glinka, J. Nicol, D. I. Margolese, a pre-formed silicate liquid crystal.21 G.D. Stucky and B. F. Chmelka, Science, 1995, 267, 1138. 18 (a) C.-Y. Chen, H.-X. Li and M. E. Davis, Microporous Mater., 1993, 2, 17; (b) C.-Y. Chen, S. L. Burkett, H.-X. Li and M. E. Davis, Conclusions Microporous Mater., 1993, 2, 27. 19 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 865. Optical birefringence patterns observed for free-standing meso- 20 D.M. Antonelli and J. Y. Ying, Angew. Chem., Int. Ed. Engl., 1995, porous silica films are shown to originate from mesoscale 34, 2014. optical anisotropy associated with the polarization response 21 (a) G. S. Attard, J. C. Glyde and C. G. Go� ltner, Nature (L ondon), of electron density circumscribing a hexagonal array of glassy 1995, 378, 366; (b) M. Antonietti and C. Goltner, Angew.Chem., silica channels. The existence of the birefringence shows that Int. Ed. Engl., 1997, 36, 910. 22 P. Behrens, Angew. Chem., Int. Ed. Engl., 1996, 35, 515. the channel architecture is a silicified replica of the defect 23 H. Yang, G. Vovk, N. Coombs, I. Sokolov and G. A. Ozin, induced pattern of director fields in a silicate liquid crystal J.Mater. Chem., 1998, 8, 743. precursor.Alteration of synthesis conditions, mixing and sub- 24 T. Tasumi, K. Koyano, Y. Tanaka and S. Nakata, Chem. L ett., strates enables control over the film texture, which reflects 1997, 469. changes in channel structure arising from the operation of 25 (a) S. J. Gregg and K. S. W. Sing, Adsorption, Surface Area and distinct film growth processes. The ability to synthesize Porosity, Academic Press, London, 2nd edn., 1982; (b) H. Naono, M.Hakuman and T. Shiono, J. Colloid Interface Sci., 1997, 186, 5–10 mm thick mesoporous silica films and tailor their channel 360; (c) M. J. Meziani, J. Zajac, D. J. Jones, J. Rozie`re and architecture can be considered to represent a significant step S. Partyka, L angmuir, 1997, 13, 5409; (d) M. Kruk, M. Jaroniec towards the practical realization of mesoporous silica thin and A. Sayari, L angmuir, 1997, 13, 6267. film-based devices and technologies. 26 H. Yang, A. Kuperman, N. Coombs, S. Mamiche-Afara and G. A. Ozin, Nature (L ondon), 1996, 379, 703. Financial support from Mobil Technology Company is deeply 27 O. Regev, L angmuir, 1996, 12, 4940. 28 Y. S. Lee, D. Surjadi and J. F. Rathman, L angmuir, 1996, 12, 6202. appreciated. H.Y. is grateful for an Ontario Graduate 29 J. Bo� cker, M. Schlenkrich, P. Bopp and J. Brickmann, J. Phys. Scholarship held during this research period. We also thank Chem., 1992, 96, 9915. Mr. G. Vovk for setting up the McBain balance and for 30 J. R. Lu, Z. X. Li, J. Smallwood, R. K. Thomas and J. Penfold, valuable discussions on data analysis, and Dr. P. Aroca for J. Phys. Chem.. 1995, 99, 8233. assistance with the recording of solid state NMR spectra. 31 H. Yang, N. Coombs and G. A. Ozin, Adv.Mater., 1997, 8, 811. 32 (a) H. W. Hillhouse, T. Okubo, J. W. van Egmond and M. Tsapatsis, Chem. Mater., 1997, 9, 1505; (b) A. Kuperman, References S. Mamiche-Afara, G. A. Ozin and H. Yang, T echnical Report to Mobil T echnology Company, June 1995. 1 K. Hiltrop, L yotropic L iquid Crystals, in L iquid Crystals, ed. 33 G. A. Ozin, H. Yang, I. Sokolov and N. Coombs, Adv. Mater., H. Stegemeyer, SteinkopV Darmstadt, Springer, Germany, 1994, 1997, 8, 662. pp. 143–171. 2 D. Demus and L. Richter, T extures of L iquid Crystals, Verlag Chemie, Weinheim, Germany, 1978. Paper 8/00004B; Received 2nd January, 1998 J. Mater. Chem., 1998, 8(5), 1205–1211

ISSN:0959-9428    

DOI:10.1039/a800004b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials EVects of preparation parameters on oxygen stoichiometry in Bi4V2O11-d† Isaac Abrahams,*a Alexandra J. Bush,a Franciszek Krok,b GeoVrey E. Hawkes,a Keith D. Sales,a Peter Thorntona and Wladyslav Boguszb aDept. of Chemistry, Queen Mary and Westfield College, University of L ondon,Mile End Road, L ondon, UK E1 4NS bInstitute of Physics, Warsaw University of T echnology, ul.Koszykowa 75, 00–662, Warsaw, Poland The eVects of various preparation parameters on vanadium reduction in Bi4V2O11-d have been investigated using EPR, 51V MAS solid state NMR and UV diVuse-reflectance spectroscopies and also SQUID magnetometry and powder neutron diVraction. The results confirm that a greater amount of vanadium reduction is observed in rapidly quenched samples and that significant oxidation occurs when samples are slow cooled.Evidence for spin–spin dipolar coupling is seen in the EPR patterns while uncoupled V4+ spins contribute to weak paramagnetic behaviour. Band gaps of around 2 eV from the UV data suggest there may be a significant electronic component to low temperature conductivities. The 51V NMR data are not inconsistent with the presence of mainly distorted octahedral and tetrahedral coordinations for vanadium.The relationship of the three major polymorphs in Bi4V2O11 Introduction can be explained with reference to a mean orthorhombic cell Fast oxide ion conducting bismuth oxide based compounds am#5.53, bm#5.61 and cm#15.28 A° ;9 for the c-phase a= have recently become of interest as solid electrolytes for b#am/Ó2, c#cm; for the b-phase a#2am, b#bm, c#cm; for applications in a variety of solid state ionic devices.1,2 The the a-phase a#3am, b#bm, c#cm. The true crystal system of materials typically used in such devices are stabilised zirconias the a-phase however has been the subject of some discussion. which possess good chemical stability but have relatively high It has been found that low levels of cationic impurities present operating temperatures, around 1073–1273 K.Certain bismuth in commercial samples of V2O5 result in an orthorhombic oxide based compounds show high conductivities with low phase for a-Bi4V2O11. However, use of high purity V2O5 yields activation energies and in some cases have shown conductivit- a phase with a small monoclinic distortion which has been ies comparable to stabilised zirconias but at significantly lower crystallographically characterised with a cell a#bm, b#cm, temperatures. c#6am, b=89.756°.10 Bismuth vanadate, Bi4V2O11, is the parent compound of an Bi4V2O11 is very sensitive to preparation conditions.extensive range of substitutional solid solutions which have Preparations by slow cooling and air quenching yield products become known as the BIMEVOX family.3–6 Bi4V2O11 shows which are visually diVerent in colour.These colour changes complex polymorphism but essentially has three main poly- are likely to be due to diVerences in the electronic structure morphs a�b (720 K) and b�c (840 K).7 Substitution of V by caused by diVering amounts of V4+.The eVect of reduction of a host of iso- and alio-valent cations leads to stabilisation of V is to increase the total number of oxide vacancies and hence the highly conducting c-polymorph to room temperature. increase the tetrahedral coordination of V. The incorporation Conductivities in the order of 10-1 S cm-1 have been reported of additional vacancies by vanadium reduction may have at 873 K for the parent compound7 and a number of the important eVects on the ionic conductivity.The true formula substituted BIMEVOXes such as BICOVOX8 and is therefore better written as Bi4V2O11-d. BICUVOX.9 The value of d has previously been investigated.12 Heating The idealised structure of Bi4V2O11 (Fig. 1) consists of samples at 1073 K in air results in a compound with d= alternating layers of [Bi2O2]n2n+ and [VO3.5&0.5]n2n-, where 2.5×10-2, while this increases to 5×10-2 under argon.It has & represents oxide ion vacancies. The [Bi2O2]n2n+ layers have basal edge-shared BiO4 square pyramidal groups with the oxygen atoms forming the basal plane and bismuth in the apical position. The vanadate layer in the idealised structure is made up of VO6 octahedra which corner share in the equatorial plane.This layer is distorted in the real structure of a-Bi4V2O11.10 In our recent defect structure determination of the Co doped material BICOVOX,11 it was found that the vacancies in the vanadate layer are concentrated in the equatorial positions around V. In addition distortion of the apical positions yields a structure in which the majority of sites are in fact distorted tetrahedral.In the structure determination of a-Bi4V2O11 both tetrahedral and octahedral V coordinations were found.10 Fig. 1 Idealised layered structure of Bi4V2O11. Small shaded circles are V, large shaded circles are Bi and unshaded circles are O atoms. † Presented at the RSC Autumn Meeting, 2–5 September 1997, University of Aberdeen, Scotland.Equatorial vacancies are not shown. J. Mater. Chem., 1998, 8(5), 1213–1217 1213been found that samples prepared under a reducing atmosphere Results and Discussion of Ar and 10% H2 yield a compound with one-third of the V Visible colour changes are observed between slow cooled and reduced, i.e. Bi4V2O10.66 which has a crystal structure best rapidly quenched samples. Samples which are furnace cooled described as Bi6V3O16.13 Under suitable conditions complete in air or oxygen show a deep red colour compared to the conversion to VIV is possible as in the structure of Bi4V2O10.14 quenched samples which are brown.The UV diVuse-reflectance However in this structure all the V are found in square spectra for samples prepared using conditions i–iv is shown in pyramidal coordination.Fig. 2. All samples show strong absorption in the blue region In this paper various preparation parameters for Bi4V2O11, but weaker absorption in the red region. That for the air such as slow cooling or air quenching, have been investigated quenched sample (i) has a stronger absorption in the red with respect to their eVects on V reduction.We have used region, thus accounting for its darker brown colour. The results SQUID magnetometry, neutron diVraction, UV diVuse reflecshow that for slow cooled samples (ii–iv) there is a clear tance spectroscopy, EPR and 51V solid state NMR to investiabsorption edge around 600 nm whereas in the air quenched gate the structural consequences of V reduction in Bi4V2O11-d. samples this absorption edge is less well defined.Clearly the results suggest a diVerence in electronic structure between slow Experimental cooled and rapidly quenched samples. We believe that this diVerence is caused by small changes in the oxygen stoichi- Preparation ometry and hence the oxidation state of V. In the slow cooled Bi4V2O11-d was prepared from Bi2O3 (Avocado 99%) and samples clear band edges are visible.For these samples band V2O5 (Aldrich 99.6%) by conventional solid state techniques. gap energies were calculated as 1.99, 2.04, and 1.98 eV for Synthesis was carried out by heating a well ground mixture of samples ii, iii and iv respectively. The air quenched sample (i) appropriate molar quantities of the starting materials at 923 K did not show a clear band edge and we were therefore unable for 6 h in a gold boat and then overnight at 1123 K.In the to calculate a band gap energy for this sample. The band gaps synthesis of samples, four types of preparation and cooling of around 2 eV compare with semiconductors such as CdSe conditions were adopted as follows: (i) preparation in air and and CdS (1.74 and 2.42 eV respectively at 300 K17).This rapid quenching from 1123 K; (ii ) preparation in flowing suggests that these materials probably show significant elecoxygen and exponential slow cooling to room temperature; tronic semiconducting behaviour at lower temperatures and (iii ) preparation in air and exponential slow cooling to room that the low temperature conductivities may have a significant temperature; (iv) preparation in air and linear slow cooling at electronimponent.It should be noted however that a rate of 25 °C h-1. measurement of oxygen transport numbers between 720 and Phase purity was confirmed by X-ray powder diVraction. 1120 K yield a near unity value suggesting that oxide ion conduction predominates at high temperatures.7 Crystallography The nominal +5 oxidation state of V is rarely achieved universally in vanadium oxides, with significant amounts of High resolution neutron diVraction data on samples i and ii V4+ in most commercial samples of V2O5.Therefore one were collected on the HRPD diVractometer at the ISIS facility, expects that in Bi4V2O11 a proportion of the vanadium will be Rutherford-Appleton Laboratory. Data were collected at room in the lower oxidation state V4+ with an electronic configur- temperature in back-scattering mode in the TOF range ation 3d1.The EPR spectra (Fig. 3) confirm the presence of 20–120 ms. The samples were placed in a V-can in the 1 m unpaired electrons in the system. position. Structure refinement was carried out using the In the structure determination of BICOVOX we described Rietveld method.All calculations were performed using the likely coordination for V, viz. distorted tetrahedra and GSAS.15 A starting model for refinement was based on the distorted octahedra.11 The tetrahedral sites arise from equa- idealised orthorhombic mean cell in space group Aba2.16 This torial vacancies in the idealised vanadate layer. The axial approach ignores the weak superlattice reflections but allows oxygens are distorted away from their ideal positions, however for a satisfactory refinement of unit cell contents.the total number of oxygens in the axial position is not less than 2 per V. Therefore all oxide ion vacancies are concentrated Spectroscopy in the equatorial layer. If only tetrahedral and octahedral 51V magic angle spinning (MAS) solid state NMR data were coordinations occur, and in Bi4V2O11 the defect structure again collected at 157.8 MHz on a Bruker AMX-600 spectrometer only shows equatorial vacancies, then the total number of using a 4 mm outer diameter rotor, and a spin rate of 12 kHz.The pulse width was 0.7 ms and 4k points were acquired for each transient, with an acquisition time of 0.02 s and a relaxation delay of 0.5 s.Typically 5000 transients were accumulated for each spectrum. Chemical shifts are reported with the high frequency positive convention and are referenced to external VOCl3 (=0 ppm). UV diVuse-reflectance spectra were collected on a Perkin- Elmer 330 spectrophotometer equipped with a dual channel diVuse reflectance attachment. Relative reflectances of low loaded samples were measured against a white reference.EPR data were collected on a Bruker 200D X-band spectrometer employing 100 kHz modulation, magnetic field markers from an NMR Gaussmeter and an external microwave frequency counter. All measurements were carried out at room temperature. Magnetic measurements Fig. 2 UV diVuse-reflectance spectra for Bi4V2O11-d prepared by (a) SQUID measurements were performed on a Quantum Design quenching in air (sample i ), ( b) exponential slow cooling under a MPMS-7 with a magnetic field of 2000 G.Measurements were dynamic oxygen flow (sample ii), (c) linear slow cooling in air (sample iv) and (d) exponentially slow cooled in air (sample iii ) carried out on samples i, ii and iv. 1214 J. Mater. Chem., 1998, 8(5), 1213–1217than in the air quenched sample.In the EPR patterns for samples that were slow cooled linearly (sample iv) the higher magnetic field signal was not observed. A half field line was seen in all samples which is likely to result from spin–spin coupling of V4+. This signal at low field was found to have a g value of 4.459 in the air quenched sample and this g value did not vary significantly between samples i–iv.The relative intensities of the resonances vary between samples and reflect the spin concentration. Table 2 summarises the g values for samples i–iv and are in good agreement with a previous study where g values of 1.9543 and 4.3449 were observed.19 The general features of solid state 51V MAS NMR spectra of oxovanadium(V) compounds have been described by Crans et al.20 51V is a quadrupolar nucleus (spin I=7/2) and the MAS spectra are a superposition of the sharper central transition (mI=+1/2�mI=-1/2) and the six broad satellite transitions. The central transition appears as a central line flanked by spinning side bands, and the intensity pattern for the powdered samples is dominated by the 51V chemical shift anisotropy.21,22 Second order quadrupolar eVects cause some distortions to the central transition, giving a shift of the central line away from the isotropic chemical shift as well as distortions of the band shape. However, it is expected that the second order quadrupole eVects are minimised in spectra measured at Fig. 3 EPR spectra of Bi4V2O11-d (a) sample i, (b) sample ii, (c) sample the highest magnetic field strengths as obtained here (14.1 T).iii, (d) sample iv The 51V MAS NMR spectra for samples i–iv are shown in Fig. 4. There are two principal centre band resonances ( labelled tetrahedral sites can be calculated as 0.5 per V. This means A and B; position invariant with MAS rate) with one weaker that the tetrahedral5octahedral ratio in the idealised V5+ high frequency spinning side band ( labelled *) from resonance system is 151.Reduction of the V is likely to introduce further A (there is the possibility of a second high frequency side equatorial vacancies and therefore increases the tetra- band). A weak low frequency spinning side band from resonhedral5octahedral ratio. ance A is overlapping with resonance B. Other features in the The powder neutron refinements are summarised in Table 1.spectra are the weak broad signals of the spinning side band As expected sample ii shows a higher oxygen content than manifold due to the partially excited satellite transitions.21 The sample i, indicating a greater degree of oxidation in the oxygen lack of a widespread manifold of spinning side bands for either slow cooled sample.The diVerence in unit cell volume between A or B indicates that these resonances have modest values for the two samples is minimal. This can be explained by consider- the chemical shift anisotropy (200–300 ppm). Resonance B is ing that any increase in cell volume through incorporation of additional oxygen is balanced by a reduction in size of the Table 2 g values calculated from the EPR spectra of samples i–iv vanadium ionic radius in changing from V4+ with an ionic radius of 0.46 A° to V5+ with an ionic radius of 0.355 A° .18 sample half field line g# 2 line From the EPR patterns shown in Fig. 3 it can be seen that the air quenched sample, i, which shows the greatest amount air quenched (sample i) 4.459 1.957 of V reduction, has the strongest signal at a g value of 1.957.oxygen slow cooled 4.485 2.235 exponentially (sample ii) Slow cooling in oxygen (sample ii) appears to shift the position slow cooled in air 4.465 1.960 of this signal to a g value of 2.235 which is accompanied by a exponentially (sample iii) change in line shape. In the case of the two samples slow slow cooled in air linearly 4.487 — cooled exponentially in the furnace (samples ii and iii ) the (sample iv) signal at higher magnetic field, g#2, becomes much weaker Table 1 Refined atomic parameters from the room temperature neutron diVraction profiles of (a) Bi4V2O11-d quenched in air [sample (i)] and (b) Bi4V2O11-d exponentially slow cooled in oxygen [sample (ii )] (estimated standard deviations are given in parentheses) atom x/a y/b z/c occupancy Uiso/A ° 2 (a) sample (i)a Bi(1) 0.4968(8) 0.1688(2) 0.000(-) 1.00(-) 0.0346(9) V(1) 0.000(-) 0.000(-) 0.0508(-) 1.00(-) 0.025(-) O(1) 0.243(3) 0.2502(5) 0.263(2) 1.00(-) 0.0215(9) O(2) 0.335(3) 0.506(3) 0.308(3) 0.55(2) 0.085(3) O(3) -0.064(1) 0.1005(6) 0.046(3) 1.00(-) 0.085(2) (b) sample (ii )b Bi(1) 0.493(1) 0.1690(2) 0.000(-) 1.00(-) 0.0156(9) V(1) 0.000(-) 0.000(-) 0.0508(-) 1.00(-) 0.025(-) O(1) 0.243(3) 0.2458(8) 0.263(3) 1.00(-) 0.007(1) O(2) 0.316(2) 0.511(2) 0.303(3) 0.63(2) 0.056(3) O(3) -0.067(1) 0.0996) 0.051(3) 1.00(-) 0.056(3) aRWP=17.13%, RP=14.37%, REX=2.13%, for 6020 data points and 570 reflections.a=5.5827(2), b=15.2283(6), c=5.5073(2) A ° , V=468.20(5) A ° 3. bRWP=10.36%, RP=8.26%, REX=1.92%, for 6020 data points and 572 reflections.a=5.5840(3), b=15.2218(9), c=5.5080(3) A ° , V=468.16(7) A ° 3. For definition of R-factors see ref. 26. J. Mater. Chem., 1998, 8(5), 1213–1217 1215Fig. 4 Solid state 51V NMR spectra for Bi4V2O11-d, (a) sample i, (b) sample ii, (c) sample iii, (d) sample iv. Resonances for distorted tetrahedral (A), octahedral (B) and square pyramidal (C) vanadium sites are indicated.clearly broader than A and there is evidence of splitting of B vanadium. It is known that in the structure of Bi4V2O10, i.e. the fully reduced system, all the vanadium is five coordinate [Fig. 4( b)–(d)] in some of the spectra. The possibility exists that this apparent splitting is the result of second order in square pyramidal coordination,14 and it is highly likely that in the partially reduced system some five coordinate vanadium quadrupole eVects on the band shape for a single resonance or, more likely, it is the result of two quite similar environments.will be present. These assignments are in contrast to those of Hardcastle Previously collated 51V NMR data have shown that, typically, resonances from tetrahedral vanadium display lower et al.24 who in a study of the composition range 151–6051 Bi2O3–V2O5 assigned a peak at approx.-425 ppm to BiVO4 values for the chemical shift anisotropy than octahedrally coordinated vanadium,23 however these values depend criti- and a peak at -510 ppm to the tetrahedral site in Bi4V2O11. Our diVraction evidence suggests that there are not significant cally upon the symmetry around vanadium.Therefore, the isotropic 51V chemical shift alone is not an absolute indicator amounts of BiVO4 present in the sample and therefore both peaks are due to the main phase Bi4V2O11. Their original of vanadium coordination number. Crystallographic data10 indicate the presence of both four and six coordinate vanadium assignment was based on the assumption that the structure of Bi4V2O11 contained V in entirely tetrahedral coordination.It and the observed uncorrected shift for resonance A is -423 ppm, which is similar to the isotropic shift reported for has since been shown that in the low temperature monoclinic form of a-Bi4V2O11 both tetrahedral and octahedral V sites BiVO4 (tetrahedral vanadium).22 The observed uncorrected shift for resonance B occurs at -510 ppm and compares with are present.10 Susceptibility plots for samples i, ii and iv, derived from the literature values for distorted octahedral oxovanadium of -500 to -536 ppm.22 We therefore assign resonance A to SQUID data, are shown in Fig. 5. Samples i and ii show classic paramagnetic behaviour with low overall magnetic susceptibil- tetrahedral vanadium and B to octahedral vanadium.The chemical shift anisotropy for resonance A is within the range ities. This paramagnetism is attributable to a small number of uncoupled V4+ spins. A small kink in the curves is seen in the derived by Crans et al.,20 for distorted four or five coordinate vanadium sites, while distorted six coordinate sites were 50–70 K region due to residual oxygen in the sample holder. This eVect is normally swamped in concentrated spin systems reported by these authors to have somewhat higher values for the chemical shift anisotropy in the range 500–700 ppm.The but is observed here due to the relatively small magnetisation. The relatively low magnitude of susceptibility observed in relative magnitudes of the chemical shift anisotropies for sites A and B indicate that both these sites are somewhat distorted sample iv suggests that in this material there is a low uncoupled spin concentration.The half field lines in the EPR data which away from regular coordination geometry, which is consistent with the crystallographic evidence. are indicative of spin–spin coupling were observed in all samples including sample iv, where the main high field signal In slow cooled samples a third resonance, C, is observed centred at around -398 ppm. We believe that this third was absent.Therefore it can be concluded that although the SQUID data reveal information on the nature of the uncoupled resonance may be due to low levels of five coordinate 1216 J. Mater. Chem., 1998, 8(5), 1213–1217square pyramidal vanadium appearing in slow cooled samples. The relatively small band gaps of around 2 eV suggest that low temperature conductivities may have a significant electronic component.We gratefully acknowledge the EPSRC for a project studentship to A.J.B. and for use of the ISIS facility at the Rutherford-Appleton Laboratory. We would like to thank Professor P. Day and Dr. S. G. L. Carling at The Royal Institution of Great Britain for use of the SQUID magnetometer, Dr.A. Aliev using the ULIRS Solid State NMR 600 mHz service at QMW and Dr. D. Oduwole at the ULIRS EPR service at QMW. References Fig. 5 Susceptibility plots of Bi4V2O11-d, synthesised by various preparation parameters, derived from the SQUID data 1 N. Q. Minh, J. Am. Ceram. Soc., 1993, 76, 563. 2 J. B. Goodenough, A. Manthiram, M.Paranthaman and Y. S. Zhen, Mater. Sci. Eng. B, 1992, 12, 357. 3 F. Abraham, J. C. Boivin, G. Mairesse and G. Nowogrocki, Solid V4+ spins in this weak system they cannot be easily related to State Ionics, 1990, 40/41, 934. the overall V4+ concentration because of the extent of spin– 4 G. Mairesse, in Fast Ion T ransport in Solids, ed. B. Scrosati, spin coupling. A. Magistris, C.M. Mari and G. Mariotto, Kluwer, Dordrecht, 1993, p.271. An important consequence of significant V reduction is that 5 J. C. Boivin, R. N. Vannier, G. Mairesse, F. Abraham and it imposes a lower solid solution limit in the substituted G. Nowogrocki, ISSI L ett., 1992, 3, 14. BIMEVOXes when compared to the ideal situation of a fully 6 S. Lazure, Ch. Vernochet, R. N. Vannier, G.Nowogrocki and oxidised system. Considering BIMEVOX solid solutions of G. Mairesse, Solid State Ionics, 1996, 90, 117. general formula Bi2V1-xMxO5.5-3x/2 (where M is a divalent 7 F. Abraham, M. F. Debreuille-Gresse, G. Mairesse and metal); in the ideal case where V is fully oxidised to V5+ and G. Nowogrocki, Solid State Ionics, 1988, 28–30, 529. 8 F. Krok, W. Bogusz, W. Jakubowski, J.R. Dygas and assuming that the solid solution mechanism involves creation D. Bangobango, Solid State Ionics, 1994, 70/71, 211. of only equatorial vacancies, as observed in the BICOVOX 9 E. Pernot, M. Anne, M. Bacmann, P. Strobel, J. Fouletier, R. N. structure,11 the limit for solid solution formation will be when Vannier, G. Mairesse, F. Abraham and G. Nowogrocki, Solid State all the possible vacancies are introduced, i.e.when all the V Ionics, 1994, 70/71, 259. sites are tetrahedral. This can be calculated to occur at x= 10 O. Joubert, A. Jouanneaux and M. Ganne, Mater. Res. Bull., 1994, 0.33. Generally for divalent substitution a lower solid solution 29, 175. 11 I. Abrahams, F. Krok and J. A. G. Nelstrop, Solid State Ionics, limit of around x=0.25 is usually observed.3 However, Lee 1996, 90, 57.et al.25 have shown that for M=Co this can be extended to 12 M. Huve, R. N. Vannier, G. Nowogrocki, G. Mairesse and G. Van the maximum of x=0.33. Observed lower solid solution limits Tendeloo, J.Mater. Chem., 1996, 6, 1339. in other systems suggest that further vacancy creation does 13 O. Joubert, A. Jouanneaux and M. Ganne, Nucl.Instrum. Methods not occur and that a possible explanation is that many of Phys. Res. B, 1995, 97, 119. these additional vacancies have already been created through 14 J. Galy, R. Enjalbert, P. Millan and A. Castro, C. R. Acad. Sci. Paris, Ser. II, 1993, 317, 43. V reduction. However, it is unlikely that these lower solid 15 A. C. Larson and R. B. Von Dreele, Los Alamos National solution limits can be explained entirely by this mechanism as Laboratory Report No.LAUR-86–748, 1987. this would imply unreasonably high V4+ concentrations. It 16 International T ables for Crystallography, Volume A, ed. T. Hahn, may well be the case that thermodynamic considerations are IUCR, Kluwer, Dordrecht, 1992. the predominant factor in determining the solid solution limit. 17 C. Kittel, in Introduction to Solid State Physics, John Wiley and Sons, Chichester, 1976, 5th edn., p.210. 18 R. D. Shannon and C. T. Prewitt, Acta Crystallogr., Sect. B, 1969, Conclusions 25, 925. 19 A. Aboukais, F. Delmaire, M. Rigole, R. Hubaut and G. Mairesse, We have shown that oxygen stoichiometry in Bi4V2O11-d is Chem. Mater., 1993, 5, 1819. greatly aVected by preparation parameters. Air quenching of 20 D. C. Crans, R. A. Felty, H. Chen, H. Eckert and N. Das, Inorg. samples preserves a high V4+ concentration, with slow cooling Chem., 1994, 33, 2427. methods in air or oxygen increasing the amount of oxidation. 21 R. H. H. Smits, K. Seshan, J. R. H. Ross and A. P. M. Kentgens, J. Phys. Chem., 1995, 99, 9169. While we have not been able to directly measure the value of 22 H. Eckert and I. E.Wachs, J. Phys. Chem., 1989, 93, 6796. d in this study, our results suggest that there is a significant 23 O. R. Lapina, V. M. Mastikhin, A. A. Shubin, V. N. Krasilinikov amount of V reduction and is reflected in the observed and K. I. Zamaraev, Prog. NMR. Spectrosc., 1992, 24, 457. diVerences in colour, magnetisation, EPR signal strength and 24 F. D. Hardcastle, I. E. Wachs, H. Eckert and D. A. JeVerson, unit cell contents. 51V NMR spectroscopy is not inconsistent J. Solid State Chem., 1991, 90, 194. with the presence of mainly distorted tetrahedral and distorted 25 C. K. Lee, G. S. Lim and A. R.West, J.Mater. Chem., 1994, 4, 1441. 26 H. M. Rietveld, J. Appl. Crystallogr., 1969, 2, 65. octahedral coordination geometry for vanadium in all samples irrespective of preparation conditions with small amounts of Paper 8/01614C; Received 25th February, 1998 J. Mater. Chem., 1998, 8(5), 1213–1217 1217

ISSN:0959-9428    

DOI:10.1039/a801614c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials EVect of compositional homogeneity on the magnetic properties of La0.7Ca0.3MnO3 Kumar P. S. Anil,a Joy P. Alias,b* and Sadgopal K. Dateb aCentre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune 411007, India bPhysical andMaterials Chemistry Division, National Chemical L aboratory, Pune 411008, India Dc magnetization and ac magnetic susceptibility have been measured in the temperature range 80–300 K for La0.7Ca0.3MnO3, synthesized by the conventional ceramic and the low temperature combustion methods and annealed at diVerent temperatures.Temperature dependence of the dc magnetization and the ac susceptibility is strongly dependent on the processing conditions resulting in compositional inhomogeneity in the samples.A sharp ferromagnetic transition is observed only for a compositionally homogeneous sample. The discovery of unusually high magnetoresistance (known as ation measurements. The ACS measurements were pursued as giant magnetoresistance, GMR) in the ferromagnetic perovsk- this technique can provide more information about magnetic ite manganites, Ln1-xCaxMnO3 (Ln=La, Pr, Nd, etc.) has ordering and the presence of other magnetic impurities in stimulated the need for a detailed study of their electrical a sample.15 transport and magnetic properties.1 Jonker and Van Santen2 first reported the onset of ferromagnetism in the system La1-xCaxMnO3.Wollan and Koehler3 made a detailed investi- Experimental gation of the magnetic structure of this system from neutron La0.7Ca0.3MnO3 was prepared by the combustion synthesis diVraction studies.The double-exchange (DE) magnetic intermethod (hereafter referred to as the combustion sample) follow- action between Mn3+ and Mn4+, as proposed by Zener, ing the literature method,12 and was annealed in air at diVerent explained the origin of ferromagnetism in these compounds.4 temperatures (600–1300 °C).In the ceramic synthesis method Recently it has been shown that small magnetic polarons are (referred in the text as the ceramic sample), the corresponding responsible for the pronounced magnetoresistance of these oxides were mixed in the required molar ratio and heated compounds at the Curie temperature.5 The GMR eVect in this initially at 1000 °C for 72 h with six intermediate grindings, system has been studied extensively using single crystals, thin and subsequently annealed in air at higher temperatures films, and polycrystalline samples derived from diVerent pro- (1000–1300 °C). The samples were characterized by powder X- cessing routes.Large variations in the Curie temperature are ray diVraction (XRD) method using a Philips PW1730 powder reported for a single composition processed by diVerent X-ray diVractometer. The powder XRD patterns of all the methods.Various types of anomalies in their structural, electrisamples revealed their single phase nature without any second- cal, and magnetic properties are also reported.6–11 The Curie ary or impurity phases. The microstructural features were temperature12 and magnetic entropy change13 of low temperaobtained using a Leica-Cambridge 440 scanning electron ture synthesized compounds (by the combustion of a urea– microscope. The Mn4+ content of the samples was estimated nitrate mixture or by the sol–gel method) are shown to depend by redox titrations using potassium permanganate and iron(II) on particle size; maximum Tc and entropy changes are obammonium sulfate solutions.The low field (at 10 Oe and served for bigger particles obtained by heating the sample at 27 Hz) ac susceptibility (ACS) studies were performed using higher temperatures. Since the GMR eVect can be controlled the mutual inductance technique in an APD cryogenics closed- by manipulating the grains and grain boundaries,14 the low cycle helium cryostat (50–300 K).The dc magnetization temperature synthesized compounds, which always give finer measurements were carried out on a EG&G PAR vibrating particles, oVer control over grain/grain-boundary related elecsample magnetometer (VSM) model 4500 attached to a Janis tronic properties. As these properties depend on the extent of compositional, magnetic, and structural homogeneities, com- liquid nitrogen cryostat (80–300 K).positional homogeneity at a microscopic level is the most desired factor as it leads to a uniform distribution of Mn3+/Mn4+ in the compound. The extent of the DE inter- Results and Discussion action between Mn3+ and Mn4+ which determines the Tc as In Fig. 1 the temperature dependence of the dc magnetization well as the sharpness of the ferromagnetic transition, and the (measured at 5000 Oe) is shown for the samples prepared by degree of resistivity anomaly at Tc, thus, may depend purely the ceramic and combustion methods and annealed at diVerent on the compositional homogeneity.temperatures. The samples annealed below 1300 °C show an In order to understand the origin of the diVerent types of initial increase in the magnetization at ca. 270 K and show a anomalies reported for the magnetic properties of the manbroad magnetic transition with no well defined transition ganites, we have studied the magnetic behavior of temperature. The ceramic sample annealed at 1000 °C and the La0.7Ca0.3MnO3 synthesized by two diVerent methods; (i) by combustion sample annealed at 1200 °C show a second broad the conventional ceramic method and (ii) by combustion transition below ca. 240 K. After annealing at 1300 °C for 48 synthesis or the urea–nitrate method, and annealed at diVerent hours, the first magnetic transition becomes sharp and is temperatures. The magnetic properties were evaluated using shifted to ca. 245 K for the combustion sample with a small low field ac susceptibility (ACS), high field dc magnetization, and field cooled (FC) and zero field cooled (ZFC) magnetiz- step in the magnetization at ca. 230 K. On the other hand, a J. Mater. Chem., 1998, 8(5), 1219–1223 1219well defined Tc#245 K is obtained for the ceramic sample annealed at 1300 °C for 48 hours. Fig. 2 shows the temperature variation of the ac susceptibility measured on the combustion samples.The samples annealed up to 1200 °C show an initial increase in the susceptibility above 260 K. After annealing at 1200 °C, the susceptibility curve shows multiple steps at lower temperatures, as well as the initial increase at ca. 265 K. Even the sample annealed at 1300 °C for 48 h shows a small step at ca. 230 K apart from the sharp transition at Tc=246 K.The magnetic transition temperature (Tc), which corresponds to the maximum in the dxac/dT curve of each sample, is indicated in Table 1. Inset A Fig. 2 shows the derivative of the susceptibility, dxac/dT, of the samples annealed at 1000 °C (curve 1) and 1300 °C (curve 2). Curve 1 is very broad with a maximum at 266 K and shoulders at ca. 270 K and ca. 245 K, whereas curve 2 shows only a sharp maximum at 246 K.The ac susceptibility behavior of the ceramic (curve 2) and combustion (curve 1) samples annealed at 1200 °C is compared in inset B. Both curves show almost identical behavior. Fig. 1 Temperature dependence of the magnetization (HA=5000 Oe) The ACS curves of the ceramic samples are shown in Fig. 3. of La0.7Ca0.3MnO3 annealed at various temperatures: (a) prepared by The natures of the ac susceptibility curves of the samples the combustion method, and (b) prepared by the ceramic method annealed up to 1200 °C are identical.As observed in Fig. 2, an initial increase in the susceptibility is observed below ca. 270 K and a second rise at low temperature is observed at 185 K for the 1000 °C annealed sample. The temperature at which this second transition occurs is shifted to higher temperatures (see Table 1) as the annealing temperature is increased to 1200 °C (193 K for curve b and 208 K for curve c) with an increase in the magnitude of the transition below 270 K, and finally both the transitions are merged together to form a single broad Fig. 2 Temperature dependence of the ac susceptibility of La0.7Ca0.3MnO3 synthesized by the combustion method and annealed at various temperatures.Inset A: the dxac/dT curves of (1) 1000 °C and (2) 1300 °C annealed samples; inset B: ACS curves of the samples Fig. 3 Temperature dependence of the ac susceptibility of annealed at 1200 °C, prepared by (1) combustion and (2) ceramic La0.7Ca0.3MnO3 synthesized by the ceramic method and annealed at methods.various temperatures Table 1 Mn4+ content and the Curie temperature(s) of the samples annealed at various temperatures (Tc corresponds to the tempreature at which the dxac/dT shows a maximum value) annealing temperature/°C; sample duration/ha Mn4+ content (%) Tc/K La0.7Ca0.3MnO3 1000; 72 34 262, 185 (ceramic) 1100; 12 32 263, 193 1200; 12 32 263, 208 1300; 12 30 249 1300; 24 30 245 1300; 48 30 245 La0.7Ca0.3MnO3 600; 12 62 264 (combustion) 800; 12 42 270 1000; 12 34 266 1200; 12 32 265, 246, 195 1300; 48 30 246 La0.9Ca0.1MnO3 1000; 72 14 265, 216 (ceramic) 1100; 12 14 263, 164 1200; 12 12 150 1300; 12 10 155 1300; 48 10 155 aThe ceramic samples initially annealed at 1000 °C; 72 h are subsequently annealed at higher temperatures. 1220 J. Mater. Chem., 1998, 8(5), 1219–1223transition for the sample annealed at 1300 °C for 12 hours.inhomogeneity only and not due to the excess of Mn4+ in La0.7Ca0.3MnO3. This can be justified with the following This magnetic transition becomes sharp for the sample annealed at 1300 °C for longer duration (Tc#245 K). reasons. (1) The Curie temperature for the first magnetic transition at ca. 263 K remains unchanged for the ceramic Fig. 4 shows the FC and ZFC curves of the ceramic sample annealed at two diVerent temperatures. The FC and ZFC samples annealed up to 1200 °C, though the Mn4+ content is decreased slightly (see Table 1). (2) If the magnetic transition curves deviate at a temperature slightly below Tc#245 K for the high temperature annealed sample, whereas for the low at ca. 263 K is due to excess Mn4+, there is no reason for a second magnetic transition at a lower temperature (Fig. 3). temperature annealed sample this deviation starts at ca. 265 K, close to the first magnetic transition observed in the ac The Curie temperature for this second transition increases with increasing annealing temperature and this transition must be susceptibility curve (Table 1).Both the FC and ZFC curves show a second magnetic transition at ca. 185 K. For the due to the presence of another phase with a diVerent composition. (3) There is not much variation in the Tc of the combustion combustion samples also similar FC and ZFC curves were obtained. sample with annealing temperature up to 1200 °C, though the estimated Mn4+ content is continuously decreased.With In La1-xCaxMnO3, maximum Tc (ca. 270 K) is observed for x=0.33, and Tc decreases as x is decreased or increased from decreasing Mn4+ content, the transition temperature is expected to be decreased. (4) The combustion sample, when this value.16 The temperature at which the dc magnetization and the ac susceptibility of the low-temperature-annealed annealed below 1200 °C and containing excess Mn4+, showed a single (broad) magnetic transition above 260 K; the same samples show an initial increase is close to the Tc of La0.67Ca0.33MnO3, indicating the presence of small amounts sample when annealed at 1200 °C showed three magnetic transitions as evidenced from three maxima in the dxac/dT of the x=0.33 phase in the samples.The onset of a first magnetic transition below ca. 270 K with a second broad curve, though this sample contained less Mn4+ compared to the low-temperature-annealed samples. magnetic transition at a lower temperature, and the absence of a well defined magnetic ordering temperature for the samples The above facts indicate that the observed anomalous magnetic behavior of those samples processed below 1300 °C annealed below 1300 °C, indicate that the samples prepared by the ceramic method and the combustion method, annealed is due to the presence of phases with varying compositions in the La1-xCaxMnO3 system.Validity for the above arguments at low temperatures, may contain diVerent compositions (diVerent x values) in the series La1-xCaxMnO3. It is possible comes from the results of Baythoun and Sales who had earlier shown by careful EDAX analysis that the samples prepared that on initial heating of the mixture of oxides (ceramic method) and in the decomposed urea–nitrate mixture (combus- by a low temperature sol–gel process and annealed at a temperature as high as 1400 °C were not compositionally tion method), phases with diVerent compositions in the entire range 0x1 are formed.On further heating of this mixture homogeneous.18 The ideal composition La0.5Sr0.5MnO3 synthesized by them at low temperatures and annealed at 1200 °C at higher temperatures, the compositional range is narrowed, and finally after heating at a higher temperature for suYcient had only 50% of the total sample within a compositional band of x between 0.4 and 0.6, with the rest of the sample having duration, the required composition is obtained.That is, the samples annealed at low temperatures are compositionally other compositions in the range 0x1 in La1 -xSrxMnO3. Similarly, after annealing at 1400 °C, 64% of the sample had inhomogeneous. The increasing FC magnetization (Fig. 4) at low temperatures for the low-temperature-annealed sample the ideal composition but the rest of the phases were between x=0.3 and x=0.6.A similar distribution of the various com- indicates the presence of a paramagnetic phase along with the ferromagnetic phase(s) in the sample. positions in La1-xCaxMnO3 is responsible for the observed magnetic behavior in our experiments. The magnetic transition The Curie temperatures of the manganites containing excess oxygen are reported to be higher than those of the stoichio- (at 245 K) of the combustion sample annealed at 1300 °C is sharper (Fig. 2) than that of the sample prepared by the metric samples, and this eVect is more pronounced for LaMnO3 and low Ca doped samples.2,17 The higher Tc of the oxygen- ceramic method and annealed under similar conditions (Fig. 3). This implies that the ceramic sample annealed at 1300 °C for excess compositions is due to the presence of an excess of Mn4+ in the compounds and a maximum Tc of ca. 270 K is 48 h is still inhomogeneous but with the additional phases having compositions above and below, but very close to, x= observed for 33% Mn4+ containing compositions. This Mn4+ content is equivalent to that present in La0.67Ca0.33MnO3, 0.3.The combustion sample, on the other hand, has two, almost fixed, compositions, one with x=0.3 and another which shows a magnetic transition at ca. 270 K.16 In the present results, however, the origin of the first with x#0.25. In order to show that the x=0.33 phase is formed initially, magnetic transition at ca. 270 K is due to compositional for low Ca doped samples also, the ACS curves of the composition La0.9Ca0.1MnO3 prepared by the ceramic method are shown in Fig. 5. For the sample annealed at 1000 °C for 72 h, a small increase in the susceptibility is observed at ca. Fig. 4 Temperature dependence of FC and ZFC magnetization (HA= Fig. 5 Temperature dependence of the ac susceptibility of La0.9Ca0.1MnO3 synthesized by the ceramic method and annealed at 100 Oe) of La0.7Ca0.3MnO3 prepared by the ceramic method and annealed at two diVerent temperatures various temperatures J.Mater. Chem., 1998, 8(5), 1219–1223 1221270 K with a broad transition at Tc#216 K. As the annealing by diVerent groups7,9,10,13 and identical Tc values for those samples processed at temperatures 1300 °C.6,7 temperature is increased, the contribution at ca. 270 K is decreased and the broad magnetic transition is shifted to lower The above arguments appear to be equally applicable to all the perovskite type compounds in the system La1-xAxMO3 temperatures and a well defined magnetic transition at 155 K is observed for the sample annealed at 1300 °C for 36 hours. (A=Ca, Sr, Ba, etc.; M=Mn, Co). For example, the compound La0.875Sr0.125MnO3 prepared at 1000 °C is reported19 to show Tc values and the Mn4+ content of this composition annealed at diVerent temperatures are compared, in Table 1, with that true paramagnetic behavior only above 360 K, the Tc of the composition with x=0.33 observed in the La1-xSrxMnO3 of the La0.7Ca0.3MnO3 ceramic sample synthesized and annealed under identical conditions.system.20 Our studies on the La1-xSrxCoO3 system also showed similar compositional inhomogeneity eVects for The broad nature of the magnetic transition as well as the apparent low-Tc of the combustion samples12 annealed at low samples processed at low temperatures.As the low-temperature-annealed samples show the presence temperatures [Fig. 1(a)] can be explained on the basis of compositional inhomogeneity.As both the ceramic and com- of phases with varying compositions between LaMnO3 and CaMnO3 which will have slightly varying lattice parameters, bustion samples processed below 1300 °C show an initial rise in the susceptibility at ca. 270 K, it can be attributed to the each peak in the powder X-ray diVraction pattern will be the sum of the individual peaks corresponding to the individual presence of the phase La0.67Ca0.33MnO3 in the samples.The sample will have diVerent compositions in La1-xCaxMnO3, phases. Therefore the overall XRD peak will be broader than that expected due to particle size broadening alone, for the whose Tc is a maximum for x=0.33 and continuously decreased as x is increased or decreased from this value. The sum of the low temperature synthesized compounds.One of the peaks in the powder XRD patterns of ceramic and combustion samples high field magnetization curves of all those phases with diVering transition temperatures will appear as a continuously increas- of La0.7Ca0.3MnO3 annealed at diVerent temperatures are shown in Fig. 6. The ceramic sample annealed at 1000 °C for ing curve as if the magnetic transition is very broad, with no well defined Curie temperature.The temperature at which 36 h shows a broad and asymmetric peak whereas after annealing at the same temperature for 72 h the shoulder at the maximum slope is obtained from the dM/dT curve (as reported in ref. 12) then corresponds to the Tc of the major phase higher angle side has disappeared. Similarly for the combustion sample annealed at 600 °C, a broad and asymmetric peak is present in the sample.For the 800 °C annealed sample, the dM/dT curve showed a broad maximum at ca. 235 K whereas observed, and the width and asymmetry of this peak are decreased after annealing at higher temperatures. Interestingly, the dxac/dT curve gave a maximum at 270 K. The dxac/dT curves of the combustion synthesized sample annealed at the grain size observed (from an SEM photograph) for the ceramic sample annealed at 1000 °C for 36 h is >1 mm which 1000 °C and 1300 °C shown in Fig. 2 (inset A) indicate that the Tc of the low temperature annealed sample is higher than is almost double that of the average grain size of the combustion sample (ca. 500 nm) annealed at 1000 °C for 12 h, though that of the high temperature annealed sample.The derivative curve of the 1000 °C annealed sample is very broad with a the width of the XRD peak is much higher for the ceramic sample. The asymmetry in the reflection of the low temperature shoulder at ca. 270 K and a broad feature below 250 K apart from the peak at 266 K, showing contribution from diVerent annealed samples indicates the presence of additional phases.Evaluation of the size of the particles from such broad and phases. These derivative curves are similar to the magnetic entropy change curves obtained by Guo et al.13 (magnetic asymmetric XRD peaks will be in error as it may not provide the actual size of the particles. The general conclusion that entropy, SM, is related to dM/dT ) and the higher entropy change for the high temperature annealed sample is then a ‘absence of any extra reflections in the powder XRD pattern is an indication of single phase nature of the compound’ is reflection of the increased homogeneity of that sample, rather than the change in the particle size as reported.Though a also not valid based on these arguments. From the present results it is concluded that for the calcium sharp increase in the magnetization at ca. 270 K for x=0.33 is reported,13 the magnetization increases continuously as the substituted lanthanum manganites, the anomalies reported in the magnetic behavior of low-temperature processed samples temperature is lowered to 78 K, and the total magnetization at this temperature is much less than that obtained for the x= 0.3 sample in the present study.The continuous increase in the magnetization below Tc as the temperature is decreased is due to the presence of ferromagnetic phase(s) which orders at a higher temperature, and paramagnetic contributions from those phases order at a relatively lower temperature (or from phases with very low Ca concentrations which are not ferromagnetic).The present results give evidence for the fact that compositional inhomogeneity is responsible for the dependence of Tc on the processing conditions. The diVerent values of Tc for the same composition, and almost identical values of Tc for diVerent compositions, in La1-xCaxMnO3, reported in the literature,6–11 thus arise due to non-homogeneity of the sample and also point to the fact that whatever the desired composition may be, the compound obtained upon processing below 1300 °C will be a mixture of diVerent phases.The eVect of compositional inhomogeneity may not be evident in the high field magnetization curves of the low temperature processed La0.67Ca0.33MnO3 (and those samples with substitution in the lanthanum site of this composition) because maximum Tc in the system La1-xCaxMnO3 is observed for x=0.33. However, if the Tc observed for this composition is less than that expected, then the observed Tc will be an indication of the major phase Fig. 6 Powder XRD pattern from the (200) plane of La0.7Ca0.3MnO3, present in the sample. This may be the reason for the large prepared by the ceramic and combustion methods, and annealed at diVerent temperatures diVerences in Tc of the composition La0.67Ca0.33MnO3 reported 1222 J.Mater. Chem., 1998, 8(5), 1219–122310 J. M. D. Coey, M. Viret, L. Ranno and K. Ounadjela, Phys. Rev. are due to compositional inhomogeneity which leads to mag- L ett., 1995, 75, 3910. netic as well as structural inhomogeneity. 11 R. Mahendiran, S. K. Tiwary, A. K. Raychaudhuri, T. V. Ramakrishnan, R.Mahesh, N. Rangavittal and C. N. R. Rao, Phys. P. S. A. K. is thankful to the University Grants Commission, Rev. B, 1996, 53, 3348. India, for financial support and Prof. D. S. Joag for his 12 R. D. Sanchez, J. Rivas, C. V. Vazquez, A. L. Quintela, continuous encouragement. M. T. Causa, M. Tovar and S. OseroV, Appl. Phys. L ett., 1996, 68, 134. 13 Z. B. Guo, Y. W.Du, J. S. Zhu, W. P. Ding and D. Feng, Phys. References Rev. L ett., 1997, 78, 1142; Z. B. Guo, J. R. Zhang, H. Huang, W. P. Ding and Y. W. 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HeV ner, L. P. Lee, M. F. Hundley, J. J. Neumeier, 19 D. N. Argyriou, J. M. Mitchell, C. D. Potter, D. G. Hinks, G. M. Luke, K. Kojima, B. Nachumi, Y. J. Uemura, D. E. J. D. Jorgensen and S. D. Bader, Phys. Rev. L ett., 1996, 76, 3826. MacLaughlin and S.-W. Cheong, Phys. Rev. L ett., 1996, 77, 1869. 20 H. Y. Hwang, S.-W. Cheong, N. P. Ong and B. Batlogg, Phys. Rev. 8 J. W. Lynn, R. W. Erwin, J. A. Borchers, Q. Huang, A. Santoro, JL ett., 1996, 77, 2041. L. Peng and Z. Y. Li, Phys. Rev. L ett., 1996, 76, 4046. 9 G. H. Rao, J. R. Sun, J. K. Liang and W. Y. Zhou, Phys. Rev. B, 1997, 55, 3742. Paper 7/08235E; Received 17th November, 1997 J. Mater. Chem., 1998, 8(5), 1219–1223 1223

ISSN:0959-9428    

DOI:10.1039/a708235e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Surface morphology study of corona-poled thin films derived from sol–gel processed organic–inorganic hybrid materials for photonics applications Yoo Hong Min,a Kwang-Sup Lee,*b Choon Sup Yoona and Lee Mi Doc aDepartment of Physics, Korea Advanced Institute of Science and T echnology, Taejon 305-701, Korea bDepartment of Macromolecular Science, Hannam University, T aejon 300-791, Korea cElectronics and T elecommunications Research Institute, P.O.Box 106, Yusong, Taejon 305-600, Korea Dye-doped and a dye-attached sol–gel films using the chromophore (E)-N-butyl-(4-{2-[4-bis(2-hydroxyethyl)amino]phenyl}- ethenyl)pyridinium tetraphenylborate (BPTP) and N,N-bis(2-hydroxyethyl)amino-N¾-methylstibazoliumtoluene-p-sulfonate (BAST) were fabricated by sol–gel processing.Surface morphology of the films was studied using an atomic force microscope. In the dye-doped film, many surface defects were observed. The morphology of the surface defects varied as a function of chromophore concentration. The shapes of the defects became more complicated as the chromophore concentration increased. On the other hand, no evidence of such defects was present in the dye-attached film and the quality of the film was high.Also for the dye-attached film, the surface was optically flat and smooth, and the surface roughness was measured to be less than 4 nm. It was found that corona poling processes also aVected the quality of the dye-attached film significantly. Corona poling with a needle electrode resulted in many irregular shaped defects in the film.However, poling with a tungsten wire stabilized the corona discharge and thus prevented the formation of defects, which led to films of excellent quality. The electro-optic coeYcient, r33, of the BPTP dye-attached film was measured to be 5.0 pm V-1 and this value was maintained even after 54 days at room temperature. Poled side-chain nonlinear optical (NLO) polymers, where The sol–gel processing technique is often utilized for fabricating inorganic polymer thin films.7 Using sol–gel processes, two organic chromophores with a large molecular hyperpolarizdi Verent types of sol–gel composite films were fabricated in ability are covalently bonded to the polymer backbone, have our experiment, namely dye-doped and dye-attached systems.been of great interest for photonics applications.1 Using such In the former the organic chromophores are physically blended a material, electro-optic modulators with a 40 GHz bandwidth with the silica matrix. The dye-attached system was obtained have already been realized at the laboratory level, and a by using the functionalized silicon alkoxide with one alkoxide number of passive and active photonic devices were also functional group substituted by an organic chromophore. successfully fabricated.2 In order to apply these sol–gel films to waveguide devices, From the initial stages of NLO polymeric materials research the optical propagation loss should be lower than 1 dB cm-1.in the mid-1980s, thermal relaxation and low values of NLO The causes of optical loss have been attributed to optical coeYcients of chromophores in these systems were the major absorption, Rayleigh scattering, nonuniform refractive index obstacles for practical applications.Since then there have been profile, defects in the film, surface roughness and surface continuous eVorts toward reducing thermal relaxation and damages generated by corona poling, etc.8 Since these factors increasing the NLO activity of the materials.3 In recent years, are closely related to the method of fabrication, and thus the in addition to enhancing these two fundamental factors, the resulting thin film quality, it is important to assess how research was extended to improve the optical quality, prodi Verent sol–gel processes and corona poling processes aVect cessability and the chemical stability of NLO materials, which the parameters mentioned above.are the properties closely related to those of matrix polymers. In this work, dye-doped and dye-attached sol–gel films with NLO polymer systems which are currently being investigated a stilbazolium salt dye were fabricated. The surface morpho- can be divided into two major categories.These include organic logies of the films obtained from diVerent sol–gel processes, polymer systems with a high glass transition temperature (Tg) curing and poling conditions were investigated using atomic polymer as a matrix,4 and cross-linked inorganic polymer force microscopy (AFM). Surface defects, the electro-optic systems.5 Among inorganic polymers, silicate glass is the most coeYcient and the photobleaching eVect are also described.studied and important. It has been reported by several research groups that the use of high Tg polymers can remarkably reduce the thermal relaxation of the molecular dipoles. Such improved stability is attributed to the restricted free volume and the Experimental chain stiVness of the polymer matrix. However, it has been Materials pointed out that organic polymers generally produce serious surface damage when poled by the corona discharge method.6 Tetraethylorthosilicate (TEOS) (Adrich) and 3-isocyanato- Using an inorganic polymer, such problems of surface damage propyl triethoxysilane (IP-TEOS) (Lancaster) were used can be easily overcome.Silicate glass has a high Tg and also as-received without any further purification.N,Nexhibits transparency in the spectral region of device appli- Dimethylformamide (DMF) (Junsei) solvent was distilled cations, hence it is considered to be an attractive alternative under reduced pressure over anhydrous magnesium sulfate. The NLO chromophores, (E)-N-butyl-(4-{2-[4-bis(2-hydroxy- to organic polymer systems.J. Mater. Chem., 1998, 8(5), 1225–1232 1225ethyl)amino]phenyl}ethenyl)pyridinium tetraphenylborate (0.0462 g, 1 M) were added and stirred for 15 days for the appropriate viscosity for spin casting to be obtained. (BPTP) and N,N-bis(2-hydroxyethyl)amino-N¾-methylstilbazoliumtoluene- p-sulfonate (BAST) were synthesized according to the methods reported elsewhere.9 Film casting and corona poling Sol–gel films were fabricated by the spin casting method.Dye-doped system. TEOS (10.0 g, 48.0 mmol) and ethanol Coating solutions were prepared by the method described in (2.2 g) were mixed in a 40 ml vial with HCl aqueous solution the previous section. The viscous sol was filtered through a (2.9 g, 2 M), which was added dropwise while stirring gently at Teflon syringe filter of 0.45 mm pore size.Thin films were spin 0 °C. Further stirring was performed at room temperature for coated on indium tin oxide (ITO) substrates with a rotation 12 h by using a magnetic spin bar with a rotation speed of speed of 1000–2000 rpm. The film thickness ranged from 400 rpm to complete the sol reaction. Then BPTP (0.302 g, 0.457 mmol) and DMF (15 ml ) were added to the sol and stirred again until the sol became viscous enough for film casting.Another batch of sol with a diVerent BPTP concentration (0.453 g, 0.686 mmol) was also prepared using the same procedure. Dye-attached system. DMF solvent (2 ml), IP-TEOS (0.394 g, 1.59 mmol) and BPTP (0.5 g, 0.76 mmol) were mixed together in a 20 ml vial and stirred at 90 °C for 3 h, during which time the bonding reaction of BPTP molecules with IP-TEOS took place to form urethane linkages.After cooling to room temperature, TEOS (0.039 g, 0.189 mmol) and HCl aqueous solution (0.0618 g, 1 M) were added. This mixture was then stirred for 10 days so that an appropriate viscosity for the spin casting might be obtained. Similarly, IP-TEOS (0.221 g, 0.895 mmol) and BAST (0.200 g, 0.425 mmol) were dissolved in DMF (2 ml) and the solution was stirred at 90 °C for 3 h to form urethane bonding between BAST molecules Fig. 2 UV–VIS absorption spectra for cured (———) and poled (- - - -) and IP-TEOS. After cooling the solution to room temperature, samples. The poling condition was at 160 °C for 2 h with an applied voltage of 13 kV. TEOS (0.0490 g, 0.235 mmol) and HCl aqueous solution Fig. 1 (a) Two diVerent types of sol–gel routes for dye-doped system (SG-I) and dye-attached system (SG-II). (b) Chemical equation shows the sol–gel monomer for SG-II where the BPTP or BAST salt-type chromophore is covalently bonded to the alkoxysilane by the urethane linkage. 1226 J. Mater. Chem., 1998, 8(5), 1225–1232Measurements UV–VIS spectra were obtained by a Shimadzu UV-3010PC spectrophotometer.The surface morphologies of the films were observed by using a Seiko SPA-300 atomic force microscope (AFM) equipped with an SPI-3700 controller. The 100 mm long cantilever for the AFM (Olympus) was microfabricated from pyramidal Si3N4 and the spring constant was 0.09 N m-1. The electro-optic coeYcient was measured at 1.3 mm by the simple reflection method proposed by Teng and Man.10 Results and Discussion Two diVerent sol–gel processes for preparing dye-doped and dye-attached systems are shown in Fig. 1. In sol–gel process I (SG-I), the sol–gel film was a physically blended composite where the NLO chromophore was merely distributed in the silica matrix without any chemical attachment. In sol–gel Fig. 3 Optical photograph of a dye-doped sol–gel film (magnification process II (SG-II), the NLO chromophore was covalently ×100) bonded to the silica matrix by using the functionalized sol–gel monomer described in Fig. 1( b). Considering the disappearance of the stretching vibration mode peak of the isocyanate group around 2300 cm-1 in the FTIR spectrum, the urethane 0.5 mm to 3 mm for the dye-attached system, depending on the viscosity and the rotation rate.However for the dye-doped linkage forming reaction between diol of the chromophore and isocyanate of IP-TEOS was assumed to proceed nearly system, only films of the thickness less than 1 mm were free of cracks. quantitatively. Fig. 2 shows the UV–VIS absorption spectra for the BPTP The alignment of molecular dipoles in the film was established by the corona poling method.The poling system con- dye-attached films prepared by the SG-II process. The spectra were measured in the wavelength range between 250 and sisted of a base and an electrode, and the whole system was covered by a glass bell jar. The base was electrically grounded 800 nm. Two samples prepared from the same film were used to investigate the poling eVect.The absorption maximum for and sat on top of a hot-plate. The atmosphere above the films was not controlled in any way. Either a stainless-steel needle the unpoled film was at 473 nm. For the poled film, the height of the absorption peak was reduced as compared with the with an edge angle of 60° or a tungsten wire of 20 mm diameter was used as an electrode. In the case of needle poling, the unpoled film, but the peak position remained the same. Considering the same curing conditions for both films, the needle electrode was positioned 2 cm above the ground with a poling voltage of 13 kV, at which a stable corona discharge reduction of the peak height can be accounted for by the corona poling eVect, which indicates the alignment of chromo- started to be generated.For the wire poling, the distance between the wire electrode and the ground was set at 1 cm phore dipoles normal to the film surface. For the dye-doped system, fabrication of sol–gel films thicker and a poling voltage of 5 kV was suYcient for generating a stable corona discharge. than 1 mm was very diYcult because of severe cracking prob- Fig. 4 AFM images of a BPTP dye-doped composite film with 0.46 mmol of BPTP, (a) 20×20 mm2, ( b) 2×2 mm2.The film was thermally cured at 150 °C for 2 h. J. Mater. Chem., 1998, 8(5), 1225–1232 1227Fig. 5 AFM images of a BPTP dye-doped composite film with 0.69 mmol of BPTP, (a) 30×30 mm2, ( b) 10×10 mm2. The film was thermally cured at 150 °C for 2 h. lems (Fig. 3). The films were very brittle and the adhesion to the ITO layer was poor.During thermal curing, the color of the dye-doped film changed from bright orange to pale yellow. The melting temperature of the chromophore was 79 °C and decomposition started at around 150 °C, as determined by thermogravimetric analysis (TGA) using a very slow heating run. Therefore, it is very likely that the change in color during the thermal treatment may be caused by decomposition and/or vaporization of chromophore molecules at elevated temperatures.The AFM images of two dye-doped sol–gel films are shown in Fig. 4 and 5. Both films have the same concentration of TEOS, ethanol and H2O, and were prepared using the same thermal curing procedures (150 °C for 2 h). The only diVerence between Fig. 4 and 5 is that the doping concentration of BPTP in the latter was 1.5 times greater than in the former, as was described in the Experimental section (0.46 mmol versus 0.69 mmol).In Fig. 4, crater-like defects with diameters of 100–200 nm and a depth of 20 nm were scattered randomly on the surface. On the other hand, in Fig. 5, canyon-like defects run in zigzag fashion, twisted and mingled together.The depth and width of these canyons were less than 20 nm and several hundred nm, respectively, and the length ranged from submicron to several mm. The present result shows that the film quality deteriorated at higher concentrations of BPTP. This may indicate that the distribution of the dye chromophore molecules becomes less inhomogeneous at the nanometer scale as the BPTP concentration increases.The maximum doping ratio of the NLO chromophore without any phase separation was about 5–6 wt.%.11 Here, no phase separation is defined as there was no observable aggregation of the dye through an optical microscope. Whether or not the distribution of the chromophores in the silica matrix was uniform on the nanometer scale could not be proved. When the concentration of chromophore exceeded a certain critical value, the film was observed to be translucent and surface defects were observed. Fig. 6(a) is the SEM micrograph of the dye-doped film containing BPTP chromophore (20 wt.%). This film was not cured so that the dye aggregations remained on the surface or inside the film. On the other hand, no aggregation was found on the Fig. 6 SEM micrographs for (a) a dye-doped film of 20 wt.% dye concentration and (b) a dye-attached film of 64 wt.% dye concentration surface of the dye-attached film [Fig. 6(b)]. 1228 J. Mater. Chem., 1998, 8(5), 1225–1232Fig. 7(a) and (b) show the AFM images, at diVerent magnifi- concentration of the chromophore increased, the film flexibility approached that of organic polymers and the adhesion to the cations, of a BPTP dye-attached sol–gel film fabricated by the SG-II route without corona poling.In this case, the thin film ITO electrode layer also improved. Fig. 7(c) and (d) shows AFM images at diVerent magnifi- was thermally cured at 160 °C for 80 min. As seen from Fig. 7(a), the surface was relatively flat and defects such as cations of the SG-II sol–gel film which was cured at 160 °C for 80 min while poling at 13 kV with a corona discharge craters or canyons could not be observed.The surface roughness was estimated to be less than 2 nm from AFM images using a needle electrode. Unevenly distributed defects, in the form of irregular-shaped craters characterized by several of higher magnification (2×2 mm2) [Fig. 7(b)]. It is believed that the reasons for the remarkable improvement of the dye- hundred nm diameters and 12–26 nm depths, were generated.These defects might been formed by the bombardment of attached film quality were that the chemical bonding of chromophore molecules to the silica matrix prevented the dye nonuniform and unstable plasma produced from the rough edge of the needle. The depths of most craters were smaller molecules from aggregating and that the chromophore molecules provided elasticity between the stiV SiO2 backbones.than the wavelength of visible light. However, the diameters were much larger than the UV–VIS wavelength. Therefore, the Such elasticity can accommodate severe contractions and hence prevent the formation of cracks [Fig. 6(b)].12 Film thicknesses scattering loss by these defects may not be neglected when used as a waveguide.of 0.5–3 mm could be fabricated in the dye-attached system and no cracks were found after the thermal treatment. As the The dye-attached sol–gel film using the NLO chromophore Fig. 7 AFM images of BPTP dye-attached sol–gel composite films: (a,b) without and (c,d) with corona poling using a needle electrode. The image sizes were 20×20 mm2 for (a,c), 2×2 mm2 for (b) and 2.5×2.5 mm2 for (d).The films were thermally cured at 160 °C for 80 min. J. Mater. Chem., 1998, 8(5), 1225–1232 1229with tosylate anion (BAST) instead of tetraphenylborate anion was also prepared by the SG-II process. AFM images for two diVerent BAST sol–gel films without and with corona poling using a needle electrode are exhibited in Fig. 8(a) and (b), respectively. The overall surface morphologies show features similar to the BPTP dye-attached sol–gel film. The surface of the cured only film is very flat and smooth [Fig. 8(a)] and the surface roughness is less than 4 nm. However, the AFM images of the BAST thin film, which was corona-poled by using a needle electrode, showed many defects of irregular shapes and sizes similar to those shown by the BPTP film [Fig. 7(c), (d)]. This problem could be overcome by using a tungsten wire electrode. Fig. 9 shows the surface morphology of a 20 mm diameter tungsten wire poled sample and nearly no surface damage can be observed. The results imply that if corona discharge is stabilized by the tungsten wire, it is possible to avoid the surface damage generated by the plasma and poled films of excellent quality can be obtained.In order to investigate the influence of corona poling on dye-attached films, cross-sectional AFM images were analyzed. As shown in Fig. 10, the surfaces of unpoled BPTP (a) and BAST (b) films are very smooth and flat. In contrast, BAST film (c) poled by the needle electrode has valleys of 3–8 nm depth and 0.8–1.2 nm width, and peaks of 3–4 nm height and 1.5–3 mm width.The results of roughness measurements are summarized in Table 1. The roughness of the BAST thin film, poled by using a needle electrode, was four times greater than those of unpoled BAST and BPTP dye-attached films. The dye-attached sol–gel film showed a good stability towards stabilized corona discharge.This obviously contrasts with the case of organic polymer systems where severe surface damage, such as cracks, pin holes, chemical reaction, surface deformation, etc., was generated.6 The endurance of the sol–gel film may be due to the strong covalent bonds which forms the SiO2 matrix. Electro-optic properties of the poled dye-attached BPTP films were investigated. Measurements on dye-doped films were not possible because of low dye concentration (lower than 5 wt.%), sublimation and/or decomposition of the dye during the poling process, and rapid thermal relaxation.The Fig. 8 AFM images (20×20 mm2) of BAST dye-attached sol–gel composite films (a) without and (b) with corona poling using a needle electrode Fig. 9 AFM image (20×20 mm2) of a BAST dye-attached sol–gel composite film.The film was poled with an applied voltage of 13 kV using 20 mm tungsten wire. (a) Top view and (b) inclined side view. 1230 J. Mater. Chem., 1998, 8(5), 1225–1232Fig. 11 Temporal stability of the electro-optic coeYcient for the SG-II sample at room temperature large area illuminator (Oriel) as the UV source in the spectral Fig. 10 (a) Cross-section of Fig. 7(a); ( b) cross-section of Fig. 8(a); and range of 320 to 450 nm. The BPTP dye-attached film was (c) cross-section of Fig. 8( b) exposed to 55 mW cm-1 UV intensity. The change of refractive index was measured at 1.3 mm as a function of exposure time Table 1 Roughness measurements of dye-attached films by using a prism coupling method. As shown in Fig. 12, the refractive index decreased exponentially.The refractive index sample Ra a/nm Rb max/nm Rc z/nm was changed by 0.028 over 3 h exposure. Fig. 13 shows the Fig. 7(a) 0.209 3.563 1.163 change of the UV–VIS absorption curve of the photobleached Fig. 8(a) 0.199 1.290 0.866 film. The absorption peak height decreased as the exposure Fig. 8(b) 1.517 9.480 4.177 time increased. However no new peak appeared as a result of photobleaching.The results suggest that the mechanism of aThe mean roughness (Ra), calculated from Ra=1/L | f (x)|dx, with f (x) photobleaching in the BPTP chromophore is not due to the profile curve and L the length of the profile curve. bRmax was cis–trans isomer transformation, as happens with azo or stil- obtained from the diVerence between the highest and lowest points on the profile.cRz was determined, which gives the mean variation between the twenty highest and twenty lowest points on the profile. electro-optic coeYcient, r33, was measured at a wavelength of 1.3 mm for the samples which were poled by a needle electrode at 160 °C for 2 h with an an applied voltage of 13 kV. The electro-optic coeYcient values at diVerent sites of a film remained the same inside a circular boundary of about 10 mm diameter. However the electro-optic coeYcient values of diVerent films varied between 3.1 and 5.0 pm V-1 with the most probable frequency at 4 pm V-1, since the poling eYciency varied greatly from time to time even under the same poling conditions. As shown in Fig. 2 the absorption peak is quite far from the wavelength used for measuring the electro-optic coeYcient.Hence the measured electro-optic coeYcient can be regarded as a non-resonant value. In corona poling, conductivity can hardly be quantified Fig. 12 Change of refractive index of the BPTP dye-attached sol–gel because the leakage current, applied electric field and conduc- film by photobleaching eVects tion area are not well defined. However an estimation of the conductivity of the film can be made for contact poling. A very large conduction was observed at elevated temperatures over 100 °C, and as a consequence the film was damaged and dc contact poling was not possible. The leakage current was about 100 mA over an electrode area of 30 mm2 in which the applied field strength was 50 V mm-1 which corresponds to a value two orders of magnitude larger than that observed in nonionic organic sol–gel films, such as 4-[N,N-di(2-hydroxyethyl) amino]-4¾-nitrostilbene (DANS diol).The large electrical conduction observed in the ionic sol–gel films would certainly reduce the poling field by draining the charges piled up on the film surface, and this could lead to a poorer poling eYciency than it might otherwise have. Therefore it is very likely that the electro-optic coeYcient values measured were underestimated.The film showed good temporal stability. The initial value of the electro-optic coeYcient remained unchanged for 54 days (Fig. 11). Fig. 13 Change of UV–VIS absorption spectrum of the BPTP dyeattached sol–gel film by photobleaching eVects Photobleaching experiments were performed by using a J.Mater. Chem., 1998, 8(5), 1225–1232 1231S. L. Kwiatkowski, G. F. Lipscomb and R. S. Lytel, Appl. Phys. bene dyes.13 However, the results support the possibility that L ett., 1991, 58, 1730. the UV radiation could break the double bond of BPTP 3 J. W. Wu, J. F. Valley, S. Ermer, E. S. Binkley, J. T. Kenny and chromophore molecules, which would then lead to the R.Lytel, Appl. Phys. L ett., 1991, 59, 2213; D. Yu, A. Gharavi and reduction of charge transfer absorption in the photobleached K. Yu, Appl. Phys. L ett., 1995, 66, 1050; M. Chen, L. R. Dalton, film. L. Yu, Y. Q. Shi and W. H. Steier,Macromolecules, 1992, 25, 4032. 4 B. K. Mandal, Y. M. Chen, J. Y. Lee, J. Kumar and S. Tripathy, Appl. Phys. L ett., 1991, 58, 3; C. Xu, B.Wu, L. R. Dalton, Conclusions P. M. Ranon, Y. Shi and W. H. Steier, Macromolecules, 1992, 25, 6716; P. M. Ranon, Y. Shi, W. H. Steier, C. Xu, B. Wu and Using sol–gel processes, a BPTP dye-doped film and BPTP, L. R. Dalton, Appl. Phys. L ett., 1993, 62, 2605; J. A. F. Boogers, BAST dye-attached films were fabricated. Surface morphology P. Th. A. Klaase, J. J. de Vlieger, D. P.W. Alkema and was studied by using AFM and many surface defects were A. H. A. Tinnemans, Macromolecules, 1994, 27, 197; C.-K. Park, observed in the dye-doped film. As the chromophore concen- J. Zieba, C.-F. Zhao, B. Swedek, W. M. K. P. Wijekoon and P. N. Prasad, Macromolecules, 1995, 28, 3713; K. M. White, tration increased, the defect concentration also increased and D. K. Kitipichai and C.V. Francis, Appl. Phys. L ett., 1995, 66, the shapes of defects became more complicated. On the other 3099; Y. Shi, W. H. Steier, L. Yu and L. R. Dalton, Appl. Phys. hand, surface defects were not observed in the dye-attached L ett., 1992, 60, 25; A. K.-Y. Jen, K. J. Drost, Y. Cai, V. P. Rao and sol–gel film. Surface roughness was measured to be less than L. R. Dalton, J.Chem. Soc., Chem. Commun., 1994, 965; T. Verbiest, a few nm. In the film poled by the needle electrode, many D. M. Burland, M. C. Jurich, V. Y. Lee, R. D. Miller and W. Volksen, Macromolecules, 1995, 28, 3005; D. Yu, A. Gharavi defects of irregular shapes were present due to nonuniform and L. Yu, Macromolecules, 1995, 28, 784; S.-K. Ham, S.-H. Choi, distribution of the corona discharge.When the corona dis- B.-H. Lee and K. Song, Polymer (Korea), 1997, 21, 201; H. K. Kim, charge was stabilized by a 20 mm diameter tungsten wire I. K. Moon, M. Y. Jin and K.-Y. Choi, Korea Polym. J., 1997, 5, 57. electrode, such defects were not observed and poled film of an 5 J. Kim, J. L. Plawsky, R. LaPerta and G. M. Korenowsky, Chem. excellent quality was obtained. Mater., 1992, 4, 249; Y.Zhang, P. N. Prasad and R. Burzynski, The electro-optic coeYcient, r33, of the poled BPTP dye- Chem. Mater., 1992, 4, 851; R. J. Jeng, Y. M. Chen, A. K. Jain, J. Kumar and S. K. Tripathy, Chem. Mater., 1992, 4, 1141; attached film was measured to be 5 pm V-1 and the film R. J. Jeng, Y. M. Chen, A. K. Jain, J. Kumar and S. K. 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ISSN:0959-9428    

DOI:10.1039/a800917a

出版商:RSC    

年代:1998

数据来源: RSC