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FEATURE ARTICLE Organic molecular solids as thin film transistor semiconductors H. E. Katz Bell L aboratories, L ucent T echnologies, 600 Mountain Avenue, Murray Hill, NJ 07974, USA The use of discrete organic compounds as active materials in transistors is described, beginning with a-sexithiophene (a-6T) and progressing to other thiophene oligomers and nonthiophene semiconductors. Device operation, molecular design, synthesis, film morphology and transport of holes and electrons are covered.Thin film transistors (TFTs) based on organic semiconductors can be fashioned directly on the gate dielectric as in Fig. 1, in an arrangement known as ‘bottom contacts’, or alternatively, are envisioned as key components of plastic circuitry for use as display drivers1 in portable computers and pagers, and as on top of the semiconductor, the so-called ‘top contact’ geometry of Fig. 2. In the former arrangement, charge need memory elements in transaction cards and identification tags.2 Such transistors are by no means expected to replace silicon only be injected laterally from the source to form the channel, while the latter alternative requires perpendicular charge trans- in high performance or high density devices, but instead are aimed at applications where ease of fabrication, mechanical port as well.This could be aided by selective doping of the semiconductor under the contacts.4 The top contact geometry flexibility and avoidance of high temperature excursions are of particular importance. Organic TFTs are just one class of has the advantage of larger and more intimate metal–semiconductor charge transfer interfaces than does the bottom contact organic devices, of which rectifiers, light-emitting diodes, photodetectors, solar cells, electro-optic switches and sensors are geometry.4 As will be discussed below, the active material can comprise two or more semiconductors, varying in bandgap, other representative examples.1,3 Since each of these latter devices would merit extensive discussion in their own right if band energy, or type, either mixed or in separate layers.The metal and dielectrics can be composed of a variety of materials treated here, they will instead be considered to be outside the scope of the present discussion, which will be devoted exclus- as well.4 Finally, the TFTs can be assembled and cascaded to form higher-order circuit elements.ively to materials issues relevant to the development of organic TFTs. The semiconductor must possess several distinct but interrelated attributes. The material must accept charge without a A generic embodiment of a TFT device is shown in Fig. 1.3 The ‘off ’ state is defined as the case of little or no current substantial barrier from the source electrode.The charge must migrate quickly between the source and the channel without flowing between the source and drain electrodes at a given source–drain voltage, while the ‘on’ state refers to the case large hysteresis. The mobility must be high enough to allow useful quantities of source–drain current to flow, modulated where substantial source–drain current flows at that voltage. Switching between the two states is accomplished by the by accessible voltage and power.The semiconductor and other materials with which it is in contact must withstand the application and removal of an electric field from the gate electrode across the gate dielectric to the semiconductor– operating conditions without thermal, electrochemical or photochemical degradation.These requirements define the neces- dielectric interface, effectively charging a capacitor. When the TFT operates in the so-called accumulation mode, the charges sary band levels, bandgaps and surface states for the semiconductors to perform, as illustrated in Fig. 3. Again, at a on the semiconductor side of the capacitor, injected from the source, are mobile and conduct the source–drain ‘channel’ ‘reasonable voltage’, the highest occupied and lowest unoccupied molecular orbitals (analogous to valence and conduction current.For ‘p-type’ semiconductors, where the organic molecules would be considered electron donors, the carriers are band energy levels in inorganic semiconductors) must be altered so that holes or electrons will enter the channel region holes, while electron-accepting organics are ‘n-type’ and form channels of electrons.In the absence of a gate field, there is as needed, without creating chemical instability.5 Too high a bandgap would probably mean that the bands themselves no channel and ideally no source–drain conduction. In practice, however, there can be adventitious off-currents caused by would be too far in energy from the voltage-modified charge carrier energies at the semiconductor interfaces.For a given impurities in the semiconductor and by leakage pathways. While the device structure is fairly specifically defined, there level of chemical or morphological defects, the probability of trap states would also increase in high bandgap materials. is some possible variability.The source and drain electrodes However, too low a bandgap or low charge carrier energies increasethe likelihood of thermal excitation or chemical doping of the materials, making them difficult to turn ‘off’. The Fig. 1 Schematic structure of an organic TFT, with the usual ‘bottom contact’ geometry. The substrate is conductive and often consists of heavily doped Si.The dielectric would then be SiO2. The source, drain and gate contacts are typically gold, but other metals or conductive Fig. 2 TFT structure illustrating the ‘top contact’ geometry composites can be used. J. Mater. Chem., 1997, 7(3), 369–376 369mobility. Thus, the mobility of several different semiconductors approached 0.1 cm2 V-1 s-1 at high dopant concentrations, but the conductivity became so high that the on/off ratio fell below 1.7 This key observation implies that molecular crystalline solids can be expected to be superior to polymeric semiconductors in TFTs.While much early TFT work was performed on conducting polymers such as polythiophene,1,8 these materials are doped almost by definition, and probably cannot be purified to the same degree as discrete molecular compounds.While the polymer mobilities may have been respectable, largely because of the doping, the on/off ratios were not utilizable. However, from a processing standpoint, polymeric materials are still advantageous in that inexpensive condensedphase deposition techniques are available that would avoid the high vacuum steps associated with the present use of molecular solid semiconductors, and thus remain attractive for further study.Unsubstituted thiophene oligomers The introduction of molecular crystals as TFT semiconductors may be credited to F. Garnier and his collaborators at CNRS, who first demonstrated devices with significant mobilities, on/off ratios and saturation behaviour using oligomeric thiophenes, chiefly the unsubstituted hexamer. The characteristics of such an early device are shown in Fig. 4. The preponderance of subsequent data on organic TFTs has also been obtained Fig. 3 Relative electronic energy levels of TFT components, under hole-injection (p-channel) and electron-injection (n-channel) using a-sexithiophene (a-6T) as the semiconductor, so it is conditions appropriate to probe the relevant chemistry, morphology and device physics of this compound in some detail.There are three principal ways to synthesize a-6T from the surfaces of the metal contacts and the surface functionality of commercially available terthiophene (a-3T), as shown in the dielectric affect these performance characteristics by influ- Scheme 1. Neutral a-3T may be oxidatively dimerized by ferric encing the interfacial charge carrier energies, determining the chloride in a nonpolar aromatic solvent, by a method described local solid state structure of the semiconductor and acting as in a European Patent Application.9 The chief advantage of sites of unwanted traps and chemical reactions.this method lies in the convenience of the reaction conditions. The two performance parameters that must be optimized in The disadvantages are the undesirably large quantity of iron TFTs are field effect mobility (mFE) and on/off ratio.The former retained in the crude solid product and the finite probability is related to the absolute quantity of ‘on’ current (Ion) that can of bond formation at carbons other than the terminal ones. be induced in the device, and is defined for the regimes where Cleaner products are obtained when the a-3T starting material current is linear with respect to source–drain voltage, and is first deprotonated with butyllithium or another strong ‘saturated’ (independent of source–drain voltage) in eqn. (1) lithium base, and then oxidized with copper(II) chloride.10 This and (2), respectively, is probably the most widely employed method, and avoids the possibility of nonselective coupling.However, a minor side Ion=[WCimFE VD(VG-VO)]/L (1) reaction occurs which places chloro groups at terminal carbons Ion=[WCimFE (VG-VO)2]/2L (2) of the a-6T product.11 Despite the low concentration of this contaminant, it is difficult or impossible to remove and could where W and L are channel width and length, respectively, Ci is the capacitance per unit area of the gate dielectric, and VD, disrupt the solid state structure of films made from the product.Therefore, a third method was developed where the oxidizing VG and VO are the drain–source, gate–source and threshold voltages, respectively. The latter expresses this current relative to the current (Ioff) that would flow in the absence of a gate field, as in eqn.(3), Ion/Ioff=mFE Ci VG/2mrrh (3) where mr and r are the mobility and density of residual charge and h is the height of the semiconducting layer. As will be discussed below, useful on/off ratios (>106) can now be obtained from several organic semiconductors. While these materials have moderate mobilities, their intrinsic conductivities can be rendered vanishingly small through proper synthesis and purification techniques, leading to very low ‘off ’ currents and lowering the denominator of the on/off ratio.Obtaining practically useful mobilities (>0.1 cm2 V-1 s-1) is not as facile,6 as the intermolecular overlaps in most organic crystals are small and near-surface crystalline morphologies are imperfect.It would therefore be tempting to increase the ‘on’ current through chemical doping. This tactic has been Fig. 4 Current–voltage plots for an early a-6T TFT [ref. 24(a)], with extensively considered, and it was concluded that the off- kind permission from Elsevier Science S.A., P.O. Box 564, 1001 Lausanne, Switzerland conduction increases more rapidly with doping level than does 370 J.Mater. Chem., 1997, 7(3), 369–376unsubstituted oligomers higher than a-3T, has proved elusive until very recently. The structure of the trimer was determined in 1989, and was found to be nearly flat, with torsional angles of 6–9°.17 The tetramer with terminal methyl groups was found to adopt a herringbone packing motif with a substantial tilt of the molecules with respect to the long unit cell axis.18 This type of structure is common to many conjugated organics and will be seen to be a harbinger of the a-6T structure in many respects.The torsional angles between thiophene rings in the dimethyl a-4T are between 3 and 4°. Several higher oligomer structures with internal alkyl and alkylthio substituents have been crystallographically determined. 19 Distortions imparted by the substituents include larger torsional angles, rotational disorder and poor intermolecular overlap. While certainly providing valuable insight, especially at the single molecule level, these compounds are not close models for the superstructures of the high oligomers. Crystalline polythiophene has been examined by X-ray diffraction, and the herringbone structure, chain planarity and alternating disposition of the thiophene rings have been established therein.20 These structural features might therefore be reasonably predicted for unsubstituted high oligomers such as a-6T.Crystal structures of a-6T were at last described in 1995.21 Carefully controlled, solventless growth procedures were used to obtain the crystal specimens. Surprisingly, two different Scheme 1 structures were found.They share the flat single molecule structure, monoclinic unit cell and herringbone packing common to several of the analogues described above. However, agent for the lithiated a-3T is ferric acetylacetonate.11,12 Besides again avoiding undesired regiochemistry, no terminally substi- they differ in the position, density and orientation of the molecules with respect to the unit cell axes.For the so-called tuted a-6T products are detected even in crude products prepared this way. ‘high temperature’ polymorph,21b shown in Fig. 5, the energy band dispersions were calculated along the three principal axes The isolation of a suitable crude product is only the first step towards obtaining device-grade a-6T.It is also necessary of the reciprocal lattice. Significant dispersions were found along two of the axes, where ‘sideways’ carbon–sulfur contacts to thoroughly triturate the crude product to remove small organic and inorganic impurities, and then recrystallize and near the van der Waals distance occur. From this calculation, it could be inferred that high mobilities would be observed in sublime the product under inert atmosphere and vacuum, respectively, before reliable device characterization can be those two dimensions.Furthermore, X-ray diffraction shows that the related oligomers a-4T and a-8T pack in arrangements attempted. Establishment of this protocol was a key step in determining reliable and encouraging performance parameters virtually identical to that of a-6T, both as bulk solids and with respect to substrate surfaces in thin film form, a prediction for a-6T in TFTs.11 These principles have also enabled high mobilities and on/off ratios to be observed in a variety of other borne out by a very recent single crystal study.22 In the initial demonstration of organic TFTs,23 it appeared compounds, as will be described later.The value of ultrapurification to organic device performance had already been well that the hexamer represented the minimum length for substantial mobility among the oligothiophenes.The value obtained, delineated for other classes of devices.6,13 a-6T Can be deposited in thin film form with a variety of on the order of 10-4 cm2 V-1 s-1, was similar to that previously observed in conjugated polymers, and was probably morphologies.The deposition temperature, evaporation rate and functionality of the substrate all influence the grain size similarly dependent on doping and defect levels. Immediately subsequent work24 indicated a strong dependence of mobility and molecular orientation of the films.14 At room temperature and slow to moderate deposition rates (<5 A° s-1) on on the nature of the gate dielectric and further emphasized the hexamer as the optimal length.A thorough and understandable polar surfaces, grain sizes on the order of 100 nm are obtained, with a preference for flat platelets containing molecules nearly model was also presented to account for the behaviour of the perpendicular to the substrate, although some parallel molecular orientation also occurs.The molecular layer spacing is 23–24 A° , close to the molecular length. Very fast deposition or a substrate temperature of 77 K produces smaller grains, molecules parallel to the substrate and slightly larger layer spacing. On the other hand, a much higher substrate temperature of 260 °C results in exclusive perpendicular molecular orientation observable by X-ray and electron diffraction, UV–VIS dichroism and conductivity anisotropy. Elongated crystallites and new polymorphs are also observed, some of which may be mesophases,15 with layer spacings distinct from those observed after room temperature deposition.The highest hole mobilities are observed with high temperature depositions because of the favourable morphology and because of the additional purification that occurs during film growth.Rapid thermal annealing or melt growth of the films leads to much larger crystalline domains, several micrometers in size, but with extensive fractures that limit the overall hole mobility.16 Fig. 5 Herringbone packing motif and unit cell definition for the ‘high temperature’ phase of a-6T The single crystal structure of a-6T, and indeed, any of the J.Mater. Chem., 1997, 7(3), 369–376 371devices, using the standard equations and also including the role of traps in determining the threshold voltage, above which the most significant gate-induced currents are observed. Finally, it was predicted that improved purification of the a- 6T would lead to higher mobilities, along with a preliminary verification.Indeed, it was later rigorously shown that improved refinement methods described above lead not only to higher mobilities, well above 0.01 cm2 V-1 s-1, but also greatly reduced off-currents, so that the on/off ratio reaches one million and the semiconductor could be described as intrinsic.11,25 Characteristics of such a device are shown in Fig. 6, where it may be noted that the current is at the detection limit at zero gate voltage, without the need for extra ‘depletion’ voltage.Improvements were also noted for a-4T and a-8T; in fact, the latter compound had mobility comparable to the hexamer, and a-4T was noteworthy for its extremely low off-current.11 A careful analysis of the film thickness and channel length dependencies of the field-induced currents showed that the channel in a-6T is confined to an extremely thin region, Fig. 7 Temperature dependence of the mobility of a-6T. The squares perhaps as thin as 50 A° , near the dielectric.25 A ‘two-dimen- are experimental data and the solid curves are fits to the Holstein theory. sional’ solid is formed, not primarily because of the morphology, which does happen to be anisotropic, but mainly because of the potential well that forms near the dielectric Unsubstituted oligothiophenes have been applied to elecinterface and that extends only one to a few monolayers tronic devices as Langmuir–Blodgett films29 as well as by outward.A hint that the mobility could be further enhanced evaporation. Besides TFTs, Schottky diodes30 and active was derived from a positive mobility dependence on source– optical devices31 have been fabricated.The interplay of optical drain voltage above 0.1 MV cm-1. These more detailed obser- and electronic effects in thiophene oligomers has recently been vations were incorporated into a more comprehensive model investigated.32 that also takes into account circuit elements arising from the unpatterned deposition of the semiconductor and features of End-substituted thiophene hexamers the external circuit.26 It has also been shown that the temperature dependence of the a-6T mobility from 4 K to ambient is The placing of substituents on oligothiophenes is an attractive nonmonotonic, with a minimum near 45 K.27 This behaviour strategy because of the possibility of electronic tuning, is consistent with Holstein’s theory for small polaron motion, increased processing options and control of the film morand data can be fitted by the same set of parameters on both phology.As discussed above, substitution anywhere other than sides of the minimum, except at the very lowest temperatures, at the 4- or 5-carbons of the terminal rings leads to severe as shown in Fig. 7. Since these parameters (polaron binding distortions of the conformation and intermolecular overlap energy and carrier–lattice coupling) are associated with bulk and would probably be unproductive. Benefits have in fact material properties, it is unlikely that the microscopic mobility been realized by the 5-alkyl substitution of a-6T.33,34 Two is limited by grain boundaries, and likely that the mobility can synthetic strategies have been developed for accomplishing be enhanced by uncovering materials for which these param- this, outlined in Scheme 2.In the first, commercially available eters are more favourable. There are also indications that alkylthiophenes are appended to 5-bromobithiophene via crystalline disorder affects the polaron binding energies. Most alkylthienylzinc reagents to form alkylterthiophenes, which are recently, using a different approach, an enhanced mobility of >0.07 cm2 V-1 s-1 has been observed by constructing transistors from single crystals of a-6T mounted on the gate dielectrics with source and drain electrodes deposited on the opposite face of the crystal.28 It is not yet known whether the single crystal is in a phase with more favourable (lower) values of the Holstein parameters, or whether the high mobility is due to the avoidance of gross cracks and contact delamination.Fig. 6 Current–voltage plots for an ‘intrinsic’ (dopant-free) a-6T TFT. Scheme 2 Note that the current scale is logarithmic. 372 J. Mater. Chem., 1997, 7(3), 369–376then lithiated and dimerized.33 A second route begins with the total heavy atoms and a different linkage compared to a-6T.The melting point of this compound is very high, over 400°C, acylation of a-3T followed by deoxygenation of the product.34 The first route avoids the limited yield associated with the and the morphology consists of smooth interconnected grains with perpendicular orientation. These favourable properties acylation step, but requires careful chromatography.The second route employs simpler chromatography because of the are best obtained when the substrate temperature is 100 °C. The conformation of the molecule would be expected to be polarity contrast of the acylterthiophene intermediate and provides greater choice over the nature of the eventual alkyl flatter than that of a-6T.At the same time, the semiconducting properties of penta- substituent. Unlike the case of the unsubstituted derivatives, CuCl2 is a suitable coupling reagent for the alkylterthienyl- cene23 were revisited.40 The mobility of pentacene turns out to be extremely sensitive to the deposition conditions. Variations lithiums because no chlorinated hexathienyls can form, and it is advantageous to utilize the relatively high reactivity of CuCl2 in the deposition rate over 1–2 orders of magnitude and substrate temperature over just tens of degrees about ambient to intercept the lithiated compounds before they can isomerize to (1-lithioalkyl) compounds. produces films ranging from 10-6 to 3×10-2 cm2 V-1 s-1.This is due to the striking changes in morphology that Dihexylated a-6T forms a much smoother, orientationally homogeneous film than does the unsubstituted parent.33 The accompany these variations.At the extremes of low temperature and/or low deposition rate, amorphous films are produced, ordered domains are larger and the hexathienyl cores are directed at a slight but consistent tilt angle relative to the while at more moderate deposition rates and slightly elevated temperatures, polycrystalline films reminiscent of thiophene substrate normal.The influence of the alkyl chains on the morphology is manifest in the three melting transitions, evi- oligomers are obtained. A novel liquid-phase deposition of a soluble pentacene Diels–Alder adduct followed by in situ dence of mesophases, observed with this compound.34 The mobility is 0.05 cm2 V-1 s-1, higher than typically achieved thermal conversion to pentacene produced a mobility of 10-3 cm2 V-1 s-1, and represents a first approach to higher- without substitution, and less prone to diminution by contaminants than that of a-6T.The dihexyl compound has been used order devices including ring oscillators and logic gates made without high-vacuum deposition of the semiconductor.2 The in devices where organic conductive leads were printed on plastic substrates.35 Use of dodecyl substituents on a-6T yields morphology of these latter films was considered to be amorphous.40 a material with mobility comparable to the parent, even though the proportional volumes of the active moieties and inert More recently, mobilities as high as 0.6 cm2 V-1 s-1 were reported for pentacene deposited at elevated temperature using substituents are comparable.36 The melting points are further lowered and the solubility is increased.It has been demon- top contact geometry.41 This is a breakthrough value for organic TFTs, similar to the hole mobility measured in highly strated that oligothiophenes with fused tetrahydrobenzo endcaps may be deposited with extremely low conductivities, purified organic single crystals such as naphthalene and anthracene using transient photoconductivity techniques,6 and also useful for low off-currents, although these films are susceptible to oxygen doping.37 approaches the electron mobility of amorphous silicon.42 The exceptional performance of this form of pentacene has been In an attempt to lower the barrier to hole injection, a-6T with hexylthio substituents was synthesized.34 Unfortunately, traced to its forming large (1–10 micron) thin film single crystal domains, on the order of the device sizes.43 Fig. 8 shows a doping and decomposition levels were too high for this material to be considered useful. Routes to additional a-6T derivatives comparison of the device characteristics and electron diffraction patterns of TFT films deposited at ambient temperature with more elaborate substituents, including polyethers and electron withdrawing substituents such as formyl and cyano, and 85°C.The high temperature electron diffraction pattern shows single crystallinity, with the long molecular axes perpen- have also been devised.38 dicular to the substrate.The highest mobility is associated with this morphology. Fused ring compounds Pentacene shares the flat ribbon shape common to the thiopheneoligomers and the benzodithiophene dimer discussed In trying to determine whether catenated thiophenes are essential to the construction of organic semiconductors, a above. However, its lack of heteratoms indicates that sulfurs are not essential for either favourable morphology or high compound with the thiophenes incorporated into fused benzodithiophene rings was prepared.39 The synthesis is based on mobility.It would still be an open question as to whether the ribbon shape is necessary. Some evidence to the contrary has what was originally reported for that ring system, followed by ferric acetylacetonate coupling (Scheme 3).A mobility of been derived from phthalocyanines, which are planar but fourfold symmetric. Fair mobilities have been reported for phthalo- 0.04 cm2 V-1 s-1 was observed, despite fewer sulfurs, fewer cyanine derivatives in highly conductive states.7 More recent work has identified phthalocyanine derivatives which show mobility comparable to a-6T and edge-on morphologies in undoped, low conductivity states.44 Thus, TFT films can conceivably be fabricated from compounds lacking sulfurs and high aspect ratios.In the course of our own compound screening, we have considered p-type compounds such as biphenylenediamines45 commonly used in organic light-emitting diodes and 5,7,12,14- tetrathiapentacene for TFTs. These compounds are not strictly planar and to date have not shown high TFT mobilities.Our present belief is that planarity is extremely important in designing high mobility p-type compounds. n-Channel organic transistors The range of organic compounds that transport predominantly electrons is much more limited than those which are effective hole transporters. The highest mobilities have been found with Scheme 3 C60-based TFTs:46 0.08 cm2 V-1 s-1 for the neat material, and J.Mater. Chem., 1997, 7(3), 369–376 373perylenetetracarboxylic dianhyride (PTCDA) and its derivatives PTCDI and NTCDA. Fig. 8 Current–voltage plots for pentacene deposited on (a) ambient- PTCDA has an electron mobility of 10-5 to 10-4 cm2 V-1 s-1 temperature and (b) 85°C (bottom figure) substrates.The insets are in TFTs.48 The low mobility is due in part to a morphology plots to determine the threshold voltages, and the electron which has the molecules lying flat on the surface of the diffractograms. dielectric. Interestingly, PTCDA transports mainly holes in the molecular stacking direction, which happens to be perpendicu- a factor of 3–4 higher for devices grown on substrates pre- lar to the direction of transport in a TFT.Slightly lower treated with tetrakis(dimethylamino)ethylene. The character- mobilities are found with substituted and unsubstituted istics are shown in Fig. 9; the signs of the gate voltage and imides,49 probably reflecting the expected lower electron affin- drain current are opposite those for p-type devices. These ities of the imides.On the other hand, NTCDA shows higher devices are all much more sensitive to the atmosphere than mobility than the more delocalized PTCDA.50 Although all of are p-type devices, partly because of the chemical sensitivity these compounds are more stable than C60, the devices again of C60 itself, and partly because of the inherent oxygen sensi- degrade rapidly with operation in air.This degradation is tivity of electrons (‘radical anions’) in organic materials. reversible, and the devices resume their normal operating Temperature- and field-effect mobility have also been measured characteristics when moisture is removed from the ambient. It for a C60/C70 mixture containing about 10% C70.47 is possible that higher apparent mobilities would arise from Another class of electron carriers are the dyes based on use of lower work function electrodes, compounds with improved morphologies or molecules with higher electron affinities.These routes are being explored.For example,tetracyanoquinodimethane has a very high electron affinity, but only a fair mobility in a highly doped state.7 One higher order effect that has been demonstrated using n-type semiconductors is related to complementary circuit fabrication. Heterostructure field effect transistors displaying distinguishable n- and p-type behaviour in the same devices have been made from thiophene hexamers as p-type materials and C60, or PTCDA as n-type.51 This double polarity behaviour is shown for a-6T/C60 in Fig. 10. The function of such a device could be determined in a circuit by the sign of the gate voltage applied to it.Circuits containing complementary transistors are important where low power dissipation is a major consideration. Summary and outlook The range of organic molecules displaying substantial semiconducting action in TFTs has been expanded to include various shapes and constitutions. Several approaches to high hole mobility have been uncovered, and electron mobility may also now be seriously considered. A major ongoing challenge is to Fig. 9 Current–voltage plots for an n-channel, C60-based TFT produce the highest mobility morphologies without the high 374 J. Mater. Chem., 1997, 7(3), 369–37615 S. Destri, M. Mascherpa and W. Porzio, Adv. Mater., 1993, 5, 43. 16 (a) L. Torsi, A. Dodabalapur, A.J. Lovinger, H. E. Katz, R. Ruel, D. D. Davis and K. W. Baldwin, Chem. Mater., 1995, 7, 2247; (b) A. J. Lovinger, D. D. Davis, A. Dodabalapur, H. E. Katz and L. Torsi, Macromolecules, 1996, 29, 4952. 17 F. Van Bolhuis, H. Wynberg, E. E. Havinga, E. W. Meijer and E. G. J. Staring, Synth. Met., 1989, 30, 381. 18 (a) S. Hotta and K. Waragai, J. Mater. Chem., 1991, 1, 835; (b) S.Hotta and K. Waragai, Adv. Mater., 1993, 5, 896. 19 (a) G. Barbarella, M. Zambianchi, R. Di Toro, M. Colonna, L. Antolini and A. Bongini, Adv.Mater., 1996, 8, 327; (b) J-H. Liao, M. Benz, E. LeGoff and M. G. Kanatzidis, Adv. Mater., 1994, 6, 135; (c) J. K. Herrema, J. Wildeman, F. van Bolhuis and G. Hadziioannou, Synth.Met., 1993, 60, 239. 20 (a) Z. Mo, K-B. Lee, Y. B. Moon, M.Kobayashi, A. J. Heeger and F. Wudl, Macromolecules, 1985, 18, 1972; (b) W. Porzio, S. Destri, M. Mascherpa, S. Rossini and S. Bru�ckner, Synth. Met., 1993, 55–57, 408. 21 (a) G. Horowitz, B. Bachet, A. Yassar, P. Lang, F. Demanze, J- Fig. 10 Current flow at constant absolute source–drain voltage in a L. Fave and F. Garnier, Chem.Mater., 1995, 7, 1337; (b) T. Siegrist, single a-6T/C60 heterostructure TFT as a function of sign and magni- R.M. Fleming, R. C. Haddon, R. A. udise, A. J. Lovinger, tude of the gate voltage. Substantial currents for both negative drain H. E. Katz, P. M. Bridenbaugh and D. D. Davis, J. Mater. Res., and gate (p-channel) and positive drain and gate (n-channel) operation 1995, 10, 2170. are observed. 22 A. J. Lovinger, D. D.Davis, A. Dodabalapur and H. E. Katz, unpublished results; D. Fichou, B. Bachet, F. Demanze, I. Billy, G. Horowitz and F. Garnier, Adv. Mater., 1996, 8, 500. 23 G. Horowitz, D. Fichou, X. Peng and F. Garnier, Synth. Met., vacuum deposition procedure, to achieve the most valuable 1991, 41–43, 1127. gains in process efficiency. Once devices are fabricated in this 24 (a)F. Garnier, G.Horowitz, X. Z. Peng and D. Fichou, Synth.Met., manner, their packaging and reliability will be an additional 1991, 45, 163; (b) G. Horowitz and P. Delannoy, J. Chim. Phys., serious concern. The issues of process sequence and long term 1992, 89, 1037. 25 A. Dodabalapur, L. Torsi and H. E. Katz, Science, 1995, 268, 270. stability should evolve as the main foci of future organic TFT 26 L.Torsi, A. Dodabalapur and H. E. Katz, J. Appl. Phys., 1995, investigations. 78, 1088. 27 L. Torsi, A. Dodabalapur, L. J. Rothberg, A. W. P. Fung and I amgrateful to my colleagues, named in many of the references, H. E. Katz, Science, 1996, 272, 1462. for a most productive collaboration. I particularly would like 28 G. Horowitz, F. Garnier, A. Yassar, R. Hajlaoui and F. Kouki, to thank A.Dodabalapur and J. Laquindanum for helpful Adv. Mater., 1996, 8, 52. suggestions regarding this manuscript. Finally, I would like to 29 (a) S. Tasaka, H. E. Katz, R. S. Hutton, J. Orenstein, G. H. Fredrickson and T. T. Wang, Synth. Met., 1986, 16, 17; acknowledge Drs T. Jackson, YenWei and D. Dimitrikopoulos (b) J. Paloheimo, P. Kuivalainen, H. Stubb, E. 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Stoldt, 402,269, 1990; FR Appl. 89/7,610, 1989; (b) T. Kurata, K. Hamano, M. S. Wever, P. Ba�uerle, M. Sokolowski, D. D. C. Bradley and S. Kubota and H. Koezuka, Organic T hin Films for Photonic E. Umbach, Synth.Met., 1996, 76, 133. Applications, Toronto, 1993, p. 186. (c) M. S. A. Abdou, X. Lu, 38 Y. Wei, Y. Yang and J-M. Yeh, Chem.Mater., 1996, 8, 2659.Z. W. Xie, F. Orfino, M. J. Deen and S. Holdcroft, Chem. Mater., 39 J. Laquindanum, H. E. Katz, A. Dodabalapur and A. J. Lovinger, 1995, 7, 631. Adv. Mater., in the press. 10 (a) J. Kagan and S. K. Arora, Heterocycles, 1983, 20, 1937; (b) M- 40 C. D. Dimitrakopoulos, A. R. Brown and A. Pomp, J. Appl. Phys., T. Zhao, B. P. Singh and P. N. Prasad, J. Chem. Phys., 1988, 1996, 80, 2501. 89, 5535. 41 Y. Y. Lin, D. J. Gundlach and T. N. Jackson, Device Research 11 H. E. Katz, L. Torsi and A. Dodabalapur, Chem. Mater., 1995, Conference, Santa Barbara, 1996, p. 175. 7, 2235. 42 Amorphous and Microcrystalline Semiconductor Devices: 12 (a) H. E. Katz and D. J. Cram, J. Am. Chem. Soc., 1984, 106, 4977; Optoelectronic Devices, ed. J. Kanicki, Artech House, Boston, 1991. (b) M. J. Marsella and T. M. Swager, J. Am. Chem. Soc., 1993, 43 J. Laquindanum, H. E. Katz, A. J. Lovinger and A. Dodabalapur, 115, 12214. Chem. Mater., 1996, 8, 2542. 13 F. F. So, S. R. Forrest, Y. Q. Shi and W. H. Steier, Appl. Phys. 44 Z. Bao, A. Dodabalapur and A. J. Lovinger, Appl. Phys. L ett., L ett., 1990, 56, 674. 1996, 69, 3066. 14 (a) B. Servet, G. Horowitz, S. Ries, O. Lagorsse, P. Alnot, A. Yassar, 45 P. M. Borsenberger, W. T. Gruenbaum, L. J. Sorriero and F. Deloffre, P. Srivastava, R. Hajlaoui, P. Lang and F. Garnier, N. Zumbulyadis, Jpn. J. Appl. Phys., 1995, 34, 1597. Chem. Mater., 1994, 6, 1809; (b) A. J. Lovinger, D. D. Davis, 46 R. C. Haddon, A. S. Perel, R. C. Morris, T. T. M. Palstra, R. Ruel, L. Torsi, A. Dodabalapur and H. E. Katz, J. Mater. Res., 1995, 10, 2958. A. F. Hebard and R. M. Fleming, Appl. Phys. L ett., 1995, 67, 121. J. Mater. Chem., 1997, 7(3), 369–376 37547 J. Paloheimo, H. Isotalo, J. Kastner and H. Kuzmany, Synth.Met., 50 J. Laquindanum, H. E. Katz, A. Dodabalapur and A. J. Lovinger, J. Am. Chem. Soc., 1996, 118, 11331. 1993, 55–57, 3185. 48 J. R. Ostrick, A. Dodabalapur, L. Torsi, A. J. Lovinger, 51 A. Dodabalapur, H. E. Katz, L. Torsi and R. C. Haddon, Science, 1995, 269, 1560. E. W. Kwock, T. M. Miller, M. Galvin and H. E. Katz, unpublished results. 49 G. Horowitz, F. Kouki, P. Spearman, D. Fichou, C. Nogues, Paper 6/05274F; Received 29th July, 1996 X. Pan and F. Garnier, Adv.Mater., 1996, 8, 242. 376 J. Mater. Chem., 1997, 7(3), 369&ndash

ISSN:0959-9428    

DOI:10.1039/a605274f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Electrocrystallization, X-ray structure and electronic properties of the dmit-based salt [MePh3P] [Ni(dmit)2]3 Anthony E. Pullen,a Hsiang-Lin Liu,b D. B. Tanner,b Khalil A. Abbouda and John R. Reynolds*a aDepartment of Chemistry, Center forMacromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611–7200, USA bDepartment of Physics, University of Florida, P.O.Box 118440, Gainesville, Florida 32611-8440, USA Electrooxidation of [Ni(dmit)2 ]-(dmit=C3S52-=4,5-dithiolate-2-thione-1,3-dithiole) in 351 acetonitrile–acetone at a Pt wire anode in the presence of methyltriphenylphosphonium bromide electrolyte yields the radical anion salt complex [MePh3P][Ni(dmit)2]3. Black shiny platelet crystals were harvested. They belong to the monoclinic space group P21/c, M= 1631.41, a=21.0872(1), b=17.4930(2), c=15.7203(2) A° , b=107.072(1)°, V=5543.4(1) A° 3 and Z=4.The crystal packing structure consists of columns of Ni(dmit)2 units of width one unit separated by columns of MePh3P+ counter-ions. The Ni(dmit)2 columns are composed of dimers of Ni(dmit)2 units with non-bonding interactions with six other pairs of Ni(dmit)2 units.The arrangement of the dimers with respect to each other in the columns has been seen in other phosphonium-based Ni(dmit)2 complexes and is similar to the packing of k-BEDT-TTF radical cation salts which have shown superconductivity. Single-crystal temperaturedependent conductivity measurements have shown that this material is semiconducting with a room-temperature conductivity of 0.1 S cm-1 and a thermal activation energy of 0.22 eV.Since the reported synthesis of the dmit (dmit=C3S52-=4,5- Ph4P+, we have replaced a phenyl group on the cation with a methyl group in order to study, not only the structural dithiolate-2-thione-1,3-dithiole) ligand,1 it has been utilized in differences, but also the electronic properties. Herein, we report an extensive amount of research along with the development the synthesis, X-ray structure analysis and temperature-depen- of a number of analogues.The research has encompassed the dent conductivity of [MePh3P][Ni(dmit)2]3 and compare its areas of coordination chemistry,2 organic chemistry3 and mateproperties to the [Me4P][Ni(dmit)2]2, [Ph4P][Ni(dmit)2 ]3 rials chemistry.4 Bis-chelate dmit complexes using squareand [(PhCH2)Ph3P][Ni(dmit)2]3 salts.6,7 planar coordinating metals (i.e.NiII, PdII, PtII ) have been used in the assembly of semiconducting, metallic and even superconducting materials. The planar structure and sulfur-rich nature Experimental of dmit allows it to form stackable close-packing structures when using square-planar coordinating metals.Also, the large Synthesis of [MePh3P][Ni(dmit)2 ]3 sulfur atomic orbitals allows for intermolecular non-bonding [Bu4N][Ni(dmit)2] was synthesized following the procedures orbital interactions.4 Currently seven different dmit-based sys- described by Hansen et al.8 The radical anion salt tems are known to have superconducting electrical properties. [MePh3P][Ni(dmit)2]3 was synthesized via constant-current The complex a-[EDT-TTF][Ni(dmit)2 ] is the latest dmit- electrocrystallization in a two-compartment glass H-cell based complex to show such electrical properties, with a Tc of equipped with Pt wire electrodes.A saturated solution of 1.3 K at ambient pressure.5 [Bu4N][Ni(dmit)2] was electrooxidized in 351 acetonitrile– The primary methods used in the search for dmit-based acetone with 0.06 mol dm-3 MePh3PBr under an argon atmos- conducting materials has been to change the counter-ion and phere.A current density of 0.9 mA cm-2 was applied over a the metal centre, with the Ni(dmit)2 system and the alkylam- period of 18 days. Black, shiny chunk-like and platelet crystals monium-based cations being the most widely studied.6 The were harvested.All solvents were degassed thoroughly prior complex [Me4N][Ni(dmit)2]2 shows superconducting behav- to use. Acetone was used as received (Aldrich) and acetonitrile iour under 7 kbar pressure with a Tc of 5.0 K.5 One class of was dried over type 4A molecular sieves (Fisher). closed-shell cations not thoroughly studied are the phosphonium- based cations.6,7 The first Ni(dmit)2 non-integer oxi- X-Ray structure determination dation state complex to be electrocrystallized using a phosphonium-based cation was [Me4P][Ni(dmit)2]2 by Kato Crystallographic data for [MePh3P][Ni(dmit)2]3 are shown and co-workers.6 The structure is composed of columns of in Table 1.Data were collected at 173 K on a Siemens SMART dimers of Ni(dmit)2 units separated by columns of Me4P+ PLATFORM equipped with a CCD area detector.A black cations. The salt exhibits semiconductivity with a single-crystal shiny platelet crystal (0.23×0.1×0.08 mm3) was chosen for room-temperature conductivity of 0.6 S cm-1. Recently we, study. along with Nakamura et al.,7 have synthesized and studied the The diffractometer was equipped with a graphite mono- 351 tetraphenylphosphonium-based complex [Ph4P][Ni- chromator utilizing Mo-Ka radiation (l=0.71073 A° ).Cell (dmit)2 ]3 . This complex exhibits a unique packing array of parameters were refined using 8192 reflections. A hemisphere Ni(dmit)2 units. The packing is characterized by stacks of of data (1381 frames) was collected using the v-scan method Ni(dmit)2 units separated by orthogonal Ni(dmit)2 spacer (0.3° frame width).The first 50 frames were remeasured at the units. The salt displays semiconducting behaviour with a end of data collection to monitor instrument and crystal single-crystal room-temperature conductivity of 7–10 S cm-1. stability (maximum correction on I<1%). Psi-scan absorption To further the understanding of phosphonium-based Ni(dmit)2 corrections were applied based on the entire data set.radical anion salts, we have synthesized the similar351 complex The structure was solved by direct methods in SHELXTL, and refined using full-matrix least-squares procedures. The [MePh3P][Ni(dmit)2]3 by electrocrystallization. Similar to J. Mater. Chem., 1997, 7(3), 377–380 377Table 1 Crystallographic data for [MePh3P][Ni(dmit)2]3 mined to be ±0.2 K or better over the temperature range measured.chemical formula C37H18Ni3PS30 formula mass 1631.41 space group P21 /c Results and Discussion a/A° 21.0872(1) b/A° 17.4930(2) Crystal structure of [MePh3P][Ni(dmit)2 ]3 c/A° 15.7203(2) The crystal structure of [MePh3P][Ni(dmit)2]3 † consists of b/degrees 107.072(1) one MePh3P+ cation and three crystallographically indepen- V /A° 3 5543.4(1) Z 4 dent Ni(dmit)2 units.The packing is characterized by columns Dc /g cm-3 1.955 of Ni(dmit)2 dimers separated by columns of MePh3P+ coun- F(000) 3276 ter-ions. The Ni(dmit)2 units are arranged in a dimeric fashion m(Mo-Ka)/cm-1 22.0 in the bc plane with the long axis of Ni(dmit)2 molecules in 2hmax/degrees 55.0 the a direction, as shown in Fig. 2. Each dimer is surrounded range of h, k, l -28–25; 0–22; 0–20 by six other dimers.Each of the dimers forms dihedral angles R1 ;a wR2b 0.034; 0.065 goodness-of-fit 1.131 of 44.5(1)° and 51.2(1)° with four other dimers along the c Drmax/e A° -3 0.545 direction and 6.7(1)° with two other dimers along the b Drmin/e A° -3 -0.499 direction. This packing motif is quite similar to both [Me4P][Ni(dmit)2]2,6 and the k-phase BEDT-TTF salts. aR1=.(||Fo|-|Fc||)/.|Fo|.bwR2=[.[w(Fo2-Fc2 )2]/.[w(Fo2 )2]]1/2; Currently the complex k-[BEDT-TTF]2{Cu[N(CN)2]Cl} w=1/[s2(Fo2)+(0.0370p)2+0.31p], p=[max(Fo2, 0)+2Fc2]/3. with this packing array has the highest superconducting transition temperature measured to date of a molecular material of 12.8 K.4 The Me4P+ complex also forms dimers of Ni(dmit)2 non-H atoms were treated anisotropically, whereas the hydro- units but in this instance, dihedral angles of 60° with four gen atoms were refined with isotropic thermal parameters. 713 other adjacent dimers and 0° with two other pairs of the six Parameters were refined in the final cycle of refinement using total surrounding dimers are observed. There are extensive 9941 reflections [with I>2s(I )] to yield R1 of 3.40%, and S,S non-bonding interdimer orbital interactions in a two- 12219 reflections to yield wR2 of 6.48%, respectively.dimensional array resulting from close contacts with distances Refinement was carried out using F2. less than the sum of the van der Waals radii (3.70 A° ). The Molecular numbering schemes for the three crystallograph- S,S distances range from 3.440 A° resulting from thiolate– ically independent Ni(dmit)2 units of [MePh3P][Ni(dmit)2]3 thiolate [S(4)–S(14)] interactions to 3.658 A° due to thiolate– are shown in Fig. 1. Selected bond lengths and angles are thiole [S(18)–S(25)] interactions. There are also several Ni located in Table 2 for [MePh3P][Ni(dmit)2]3. dz2,S non-bonding interdimer interactions observed in the crystal lattice.These range from 3.232 A° due to Ni dz2–thiole Conductivity measurements [Ni(3)–S(9)] orbital overlap to 3.856 A° due to Ni dz2–thiolate Temperature-dependent (300–150 K) resistances were meas- [Ni(2)–S(24)] orbital interactions. ured by a four-probe method using an ac technique. Two Within the dimers, the Ni(dmit)2 units stack in an eclipsed single-crystal platelets of [MePh3P][Ni(dmit)2]3 (typically fashion.Two of the three crystallographically independent 0.91×0.46×0.09 mm3) were measured in this study. Narrow- Ni(dmit)2 units are in dimers with the units being slightly gauge (0.02 mm diameter) gold wires were affixed to the crystal slipped (transverse offset) from perfectly eclipsed, as shown by using fast drying gold paint.The sample was anchored ther- the view down the c axis in Fig. 3. These Ni(dmit)2 units form mally to the cold head of a closed-cycle refrigerator (CTI dimers with intradimer spacings ranging from 3.443 to 3.652 A° . Cryogenics). A typical run was performed by first cooling the The third crystallographically independent Ni(dmit)2 forms a sample to the lowest temperature, and then taking the data dimer with a perfectly eclipsed stacking motif.This is mediated while warming. Temperature reproducibility has been deter- by strong Ni dz2,Ni dz2 orbital interactions which is shown by the solid line in the packing diagram in Fig. 2. The distance is only 2.7837(7) A° between the Ni atoms. This results in a fold-like dmit–Ni–dmit dihedral angle of 13.0° of the dmit ligand planes from 0° for a perfectly square-planar complex.To our knowledge, this very short Ni,Ni interaction resulting from dimers arranged in an eclipsed fashion is unique among Ni(dmit)2-based complexes. This has been observed in several instances with Pd(dmit)24–6,9 and Pt(dmit)2-based materials.4,10 The above-described packing of the anions and cations in [MePh3P][Ni(dmit)2]3 is significantly different from the other similar 351 phosphonium-based complexes [Ph4P] [Ni(dmit)2]3 and [(PhCH2)Ph3P][Ni(dmit)2]3 but very similar to the 251 salt [Me4P][Ni(dmit)2]2.6,7 The Ph4P+ salt displays a unique packing scheme amongst the Ni(dmit)2 complexes, with stacks of Ni(dmit)2 units separated by orthogonal spacer Ni(dmit)2 units.By simply adding a methylene spacer to one of the phenyl groups, all of the Ni(dmit)2 molecules of [(PhCH2)Ph3P][Ni(dmit)2]3 are arranged in parallel planes.By replacing a phenyl group with a methyl † Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Fig. 1 Thermal ellipsoid drawings (50% probability) and numbering Centre (CCDC).See Information for Authors, J. Mater. Chem., 1997, Issue 1. Any request to the CCDC for this material should quote the schemes for the three crystallographically independent Ni(dmit)2 moieties in [MePh3P][Ni(dmit)2]3 full literature citation and the reference number 1145/25. 378 J. Mater. Chem., 1997, 7(3), 377–380Table 2 Bond lengths (A° ) and angles (degrees) for the crystallographically independent Ni(dmit)2 units of [MePh3P][Ni(dmit)2]3 Ni(1)MS(7) 2.1856(8) S(9)MC(6) 1.732(3) S(15)MC(13) 1.707(3) S(22)MC(21) 1.730(3) Ni(1)MS(4) 2.1871(8) S(9)MC(5) 1,737(3) S(16)MC(14) 1.700(3) S(22)MC(22) 1.750(3) Ni(1)MS(5) 2.1890(8) S(10)MC(6) 1,640(3) S(17)MC(15) 1.697(3) S(23)MC(21) 1.741(3) Ni(1)MS(6) 2.2106(8) C(2)MC(3) 1.390(4) S(18)MC(16) 1.737(3) S(23)MC(23) 1.744(3) Ni(1)MNi(1)a 2.7837(7) C(4)MC(5) 1.394(4) S(18)MC(14) 1.743(3) S(24)MC(22) 1.713(3) S(1)MC(1) 1.634(3) Ni(2)MS(14) 2.1595(8) S(19)MC(16) 1.735(3) S(25)MC(23) 1.715(3) S(2)MC(1) 1.740(3) Ni(2)MS(15) 2.1660(8) S(19)MC(15) 1.739(3) S(26)MC(24) 1.696(3) S(2)MC(2) 1.745(3) Ni(2)MS(17) 2.1614(8) S(20)MC(16) 1.641(3) S(27)MC(25) 1.697(3) S(3)MC(3) 1.739(3) Ni(2)MS(16) 2.1614(8) C(12)MC(13) 1.382(4) S(28)MC(26) 1.738(3) S(3)MC(1) 1.746(3) S(11)MC(11) 1.650(3) C(14)MC(15) 1.388(4) S(28)MC(24) 1.741(3) S(4)MC(2) 1.693(3) S(12)MC(11) 1.729(3) Ni(3)MS(26) 2.1615(8) S(29)MC(26) 1.740(3) S(5)MC(3) 1.690(3) S(12)MC(12) 1.745(3) Ni(3)MS(27) 2.1670(8) S(29)MC(25) 1.742(3) S(6)MC(4) 1.695(3) S(13)MC(11) 1.741(3) Ni(3)MS(25) 2.1712(8) S(30)MC(26) 1.641(3) S(7)MC(5) 1.686(3) S(13)MC(13) 1.745(3) Ni(3)MS(24) 2.1749(8) C(22)MC(23) 1.372(4) S(8)MC(4) 1.744(3) S(14)MC(12) 1.705(3) S(21)MC(21) 1.654(3) C(24)MC(25) 1.393(4) S(8)MC(6) 1.746(3) S(7)MNi(1)MS(4) 170.92(3) C(2)MC(3)MS(3) 116.6(2) S(11)MC(11)MS(12) 123.3(2) C(21)MS(22)MC(22) 97.44(14) S(7)MNi(1)MS(5) 85.21(3) S(5)MC(3)MS(3) 122.0(2) S(11)MC(11)MS(13) 122.9(2) C(21)MS(23)MC(23) 97.11(14) S(4)MNi(1)MS(5) 92.20(3) C(5)MC(4)MS(6) 121.5(2) S(12)MC(11)MS(13) 113.7(2) C(22)MS(24)MNi(3) 101.69(10) S(7)MNi(1)MS(6) 92.29(3) C(5)MC(4)MS(8) 115.1(2) C(13)MC(12)MS(14) 120.9(2) C(23)MS(25)MNi(3) 102.18(10) S(4)MNi(1)MS(6) 88.89(3) S(6)MC(4)MS(8) 123.4(2) C(13)MC(12)MS(12) 115.6(2) C(24)MS(26)MNi(3) 102.94(10) S(5)MNi(1)MS(6) 170.71(3) C(4)MC(5)MS(7) 121.8(2) S(14)MC(12)MS(12) 123.5(2) C(25)MS(27)MNi(3) 102.76(10) S(7)MNi(1)MNi(1)a 101.01(3) C(4)MC(5)MS(9) 116.7(2) C(12)MC(13)MS(15) 120.9(2) C(26)MS(28)MC(24) 97.17(14) S(4)MNi(1)MNi(1)a 87.95(3) S(7)MC(5)MS(9) 121.5(2) C(12)MC(13)MS(13) 116.2(2) C(26)MS(29)MC(25) 97.27(14) S(5)MNi(1)MNi(1)a 97.09(3) S(10)MC(6)MS(9) 121.9(2) C(15)MC(13)MS(13) 122.9(2) S(21)MC(21)MS(22) 123.8(2) S(6)MNi(1)MNi(1)a 92.16(3) S(10)MC(6)MS(8) 124.4(2) C(15)MC(14)MS(16) 121.1(2) S(21)MC(21)MS(23) 122.8(2) C(1)MS(2)MC(2) 97.53(14) S(9)MC(6)MS(8) 113.7(2) C(15)MC(14)MS(18) 116.0(2) S(22)MC(21)MS(23) 113.5(2) C(3)MS(3)MC(1) 97.02(14) S(14)MNi(2)MS(15) 93.11(3) S(16)MC(14)MS(18) 122.9(2) C(23)MC(22)MS(24) 122.0(2) C(2)MS(4)MNi(1) 102.45(10) S(14)MNi(2)MS(17) 177.89(3) S(16)MC(14)MS(18) 122.9(2) C(23)MC(22)MS(22) 115.6(2) C(3)MS(5)MNi(1) 102.51(10) S(15)MNi(2)MS(17) 85.64(3) C(14)MC(15)MS(17) 121.1(2) C(22)MC(23)MS(25) 120.8(2) C(4)MS(6)MNi(1) 101.61(10) S(14)MNi(2)MS(16) 88.13(3) C(14)MC(15)MS(19) 115.7(2) C(22)MC(23)MS(23) 116.3(2) C(5)MS(7)MNi(1) 102.47(10) S(15)MNi(2)MS(16) 177.90(3) S(17)MC(15)MS(19) 123.2(2) S(25)MC(23)MS(23) 122.9(2) C(4)MS(8)MC(6) 97.34(14) S(17)MNi(2)MS(16) 93.07(3) S(20)MC(16)MS(19) 123.1(2) C(25)MC(24)MS(26) 120.8(2) C(6)MS(9)MC(5) 97.14(14) C(11)MS(12)MC(12) 97.50(14) S(20)MC(16)MS(18) 123.3(2) C(25)MC(24)MS(28) 116.1(2) S(1)MC(1)MS(2) 123.3(2) C(11)MS(13)MC(13) 96.16(14) S(19)MC(16)MS(18) 113.6(2) S(26)MC(24)MS(28) 123.1(2) S(1)MC(1)MS(3) 123.2(2) C(12)MS(14)MNi(2) 102.50(10) S(26)MNi(3)MS(27) 92.66(3) C(24)MC(25)MS(27) 120.8(2) S(2)MC(1)MS(3) 113.5(2) C(13)MS(15)MNi(2) 102.44(10) S(26)MNi(3)MS(25) 178.64(3) C(24)MC(25)MS(29) 115.7(2) C(3)MC(2)MS(4) 121.4(2) C(14)MS(16)MNi(2) 102.24(10) S(27)MNi(3)MS(25) 86.35(3) S(27)MC(25)MS(29) 123.5(2) C(3)MC(2)MS(2) 115.3(2) C(15)MS(17)MNi(2) 102.51(10) S(26)MNi(3)MS(24) 87.78(3) S(30)MC(26)MS(28) 122.7(2) S(4)MC(2)MS(2) 123.2(2) C(16)MS(18)MC(14) 97.09(14) S(27)MNi(3)MS(24) 176.61(3) S(30)MC(26)MS(29) 123.5(2) C(2)MC(3)MS(5) 121.4(2) C(16)MS(19)MC(15) 97.44(14) S(25)MNi(3)MS(24) 93.26(3) S(28)MC(26)MS(29) 113.8(2) aSymmetry transformations used to generate equivalent atoms: -x, -y, -z+2.Fig. 3 View perpendicular to the Ni(dmit)2 moieties showing intradimer quasi-eclipsed stacking arrangements of the moieties of [MePh3P][Ni(dmit)2 ]3.Also shown are the dimers packed in a columnar arrangement separated by MePh3P+ cations. Dashed lines represent S,S distances less than the sum of the van der Waals radii. Fig. 2 View along the long axis of the Ni(dmit)2 moieties showing a dimeric packing arrangement in [MePh3P][Ni(dmit)2 ]3 [MePh3P+ cations have been omitted for clarity]. Also shown are extensive S,S tivity decreases rapidly from its 300 K value of 0.1 S cm-1 with and Ni dz2,S (A) and Ni dz2,Ni dz2 (——) non-bonding orbital interactions. decreasing temperature.The temperature-dependent conductivity is well fit by eqn. (1), group, the material [MePh3P][Ni(dmit)2]3 results with the s(T )=s0 exp(-Ea/kBT ) same stoichiometry but with a very different packing. The with a thermal activation energy Ea of 220 meV.The room- complex [Me4P][Ni(dmit)2]2 with a 251 stoichiometry due temperature conductivity is two orders of magnitude smaller to the small size of the cation, has a packing of the Ni(dmit)2 than that of [Ph4P][Ni(dmit)2]37 and similar to the value moieties identical to that of [MePh3P][Ni(dmit)2]3. reported for [(PhCH2)Ph3P][Ni(dmit)2]3 (0.2 S cm-1) and [Me4P][Ni(dmit)2]2 (0.6 S cm-1).6 Moreover, the value of the Electrical conductivity thermal activation energy is about 20 times larger than that of [Ph4P][Ni(dmit)2]3.Thus, although both [MePh3P] The temperature dependence of the four-probe is shown in Fig. 4. Semiconducting behaviour is illustrated as the conduc- [Ni(dmit)2]3 and [Ph4P][Ni(dmit)2 ]3 have the same stoichio- J. Mater. Chem., 1997, 7(3), 377–380 3792 V.E. Shklover, S. S. Nagapetyan and Y. T. Struchkov, Usp. Khim., 1990, 59, 1179; R. M. Olk, B. Olk, W. Dietzsch, R. Kirmse and E. Hoyer, Coord. Chem. Rev., 1992, 117, 99. 3 N. Svenstrup and J. Becher, Synthesis, 1995, 215. 4 P. Cassoux and L. V. Interrante, Comments Inorg. Chem., 1991, 12, 47; P. Cassoux, L. Valade, H. Kobayashi, A. Kobayashi, R.A. Clark and A. E. Underhill, Coord. Chem. Rev., 1991, 110, 115; J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H. H. Wang, A. M. Kini and M. H. Whangbo, Organic Superconductors (Including Fullerenes), Prentice Hall, Englewood Cliffs, NJ, 1992; P. Cassoux and L. Valade, in Inorganic Materials, ed. D. W. Bruce and D. O’Hare, Wiley, Chichester, 1992, pp. 1–58. 5 M. Bousseau, L. Valade, J. P. Legros, P. Cassoux, M. Garbauskas and L. V. Interrante, J. Am. Chem. Soc., 1986, 108, 1908; L. Brossard, M. Ribault, M. Bousseau, L. Valade and P. Cassoux, C. R. Acad. Sci. (Paris), Se�rie II, 1986, 302, 205; L. Brossard, M. Ribault, L. Valade and P. Cassoux, Physica B & C (Amsterdam), 1986, 143, 378; A. Kobayashi, A. Kim, Y. Sasaki, R. Kato, H. Kobayashi, S.Moriyama, Y. Nishio, K. Kajita and W. Sasaki, Chem. L ett., 1987, 1819; K. Kajita, Y. Nishio, S. Moriyama, R. Kato, H. Kobayashi and W. Sasaki, Solid State Commun., 1988, 65, 361; L. Brossard, H. Hurdequint, M. Ribault, L. Valade, J. P. Legros and P. Cassoux, Synth. Met., 1988, 27, B157; Fig. 4 Dc conductivity for [MePh3P][Ni(dmit)2]3 as a function of L. Brossard, M. Ribault, L.Valade and P. Cassoux, J. Phys. (Paris), temperature 1989, 50, 1521; A. Kobayashi, H. Kobayashi, A. Miyamoto, R. Kato, R. A. Clark and A. E. Underhill, Chem. L ett., 1991, 2163; H. Kobayashi, K. Bun, T. Naito, R. Kato and A. Kobayashi, Chem. metry, the electrical properties of these materials are dominated L ett., 1992, 1909; H. Tajima, M. Inokuchi, A. Kobayashi, by the differences in packing caused by differences in counter- T.Ohta, R. Kato, H. Kobayashi and H. Kuroda, Chem. L ett., 1993, ion structure. 1235. It has long been advocated that molecular systems are 6 R. Kato, H. Kobayashi, H. Kim, A. Kobayashi, Y. Sasaki, T. Mori advantageous owing to their tailorability by the chemist to and H. Inokuchi, Synth. Met., 1988, 27, B359; P. Cassoux, L.Brossard, M. Tokumoto, H. Kobayashi, A. Moradpour, D. Zhu, ‘fine tune’ a system to potentially yield improved material M. Mizuno and E. Yagubskii, Synth. Met., 1995, 71, 1845; properties. We have seen from the results for [MePh3P] A. Errami, C. J. Bowlas, F. Menou, C. Faulmann, F. Gangneron, [Ni(dmit)2 ]3 , [(PhCH2)Ph3P][Ni(dmit)2]3, [Me4P] L. Valade, P. Cassoux, K. Lahlil and A.Moradpour, Synth. Met., [Ni(dmit)2 ]2 and [Ph4P][Ni(dmit)2]3 that although the com- 1995, 71, 1895; C. Faulmann, A. Errami, B. Donnadieu, I. Malfant, ponents of the materials, such as the counter-ion, can be J. P. Legros, P. Cassoux, C. Rovira and E. Canadell, Inorg. Chem., changed only slightly, very different unexpected and unpredict- 1996, 35, 3856. 7 T. Nakamura, A. E. Underhill, A.T. Coomber, R. H. Friend, able structural and electrical properties may result. This has H. Tajima, A. Kobayashi and H. Kobayashi, Inorg. Chem., 1995, been seen not only in this series of phosphonium-based 34, 870; T. Nakamura, A. E. Underhill, T. Coomber, R. H. Friend, Ni(dmit)2 salts, but also within other families (i.e. ammonium, H. Tajima, A. Kobayashi and H. Kobayashi, Synth.Met., 1995, 70, sulfonium) of Ni(dmit)2 salts.4,6,7 1061; H. L. Liu, D. B. Tanner, A. E. Pullen, K. A. Abboud and J. R. Reynolds, Phys. Rev. B, 1996, 53, 10557. This work was funded by grants from the Air Force Office of 8 T. K. Hansen, J. Becher, T. Jorgensen, K. S. Varma, R. Khedekar and M. P. Cava, Org. Synth., 1995, 73, 270. Scientific Research (F49620-96-1-0067 and F49620-93-1-0322) 9 C. Faulmann, J. P. Legros, P. Cassoux, J. Cornelissen, L. Brossard, for work completed in the Chemistry Department and the M. Inokuchi, H. Tajima and M. Tokumoto, J. Chem. Soc., Dalton National Science Foundation (DMR-9403894) for the work T rans., 1994, 249; R. Kato, Y. L. Liu, H. Sawa, S. Aonuma, completed in the Physics Department. We also acknowledge A. Ichikawa, H. Takahashi and N. Mori, Solid State the National Science Foundation for funding the purchase of Commun., 1995, 94, 973; A. Kobayashi, A. Sato, K. Kawano, the X-ray equipment. T. Naito, H. Kobayashi and T. Watanabe, J. Mater. Chem., 1995, 5, 1671. 10 M. L. Doublet, E. Canadell, J. P. Pouget, E. B. Yagubskii, J. Ren References and M. H. Whangbo, Solid State Commun., 1993, 88, 699. 1 G. Steimecke, R. Kirmse and E. Hoyer, Z. Chem., 1975, 15, 28; G. Steimecke, H. J. Sieler, R. Kirmse and E. Hoyer, Phosphorus Paper 6/06026I; Received 2nd September, 1996 Sulfur, 1979, 7, 49. 380 J. Mater. Chem., 1997, 7(3), 377–3

ISSN:0959-9428    

DOI:10.1039/a606026i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Synthesis and X-ray crystal structure of a vinylogue of tetramethyltetraselenafulvalene Martin R. Bryce,* Antony Chesney, Shimon Yoshida, Adrian J. Moore, Andrei S. Batsanov and Judith A. K. Howard Department of Chemistry, University of Durham, Durham, UK DH1 3L E Efficient syntheses of 2,2¾-ethanediylidenebis(4,5-dimethyl-2H-1,3-diselenole) 14 and the 1,3-dithiole analogue 16 are described. Cyclic voltammetry establishes that they are efficient p-electron donors. The molecular structures of 14 and 16 have been determined by single crystal X-ray analysis: the crystals are isomorphous and the molecules form planar layers parallel to the crystallographic (10 2) plane.The study of molecular conductors1 has progressed rapidly which is a charge-density wave localisation inherent to one dimensional conducting systems.5 since the discovery that the charge-transfer complex of the pelectron donor tetrathiafulvalene (TTF) 1 and the p-electron The incorporation of conjugated alkene linking groups between the two 1,3-dithiole rings of TTF has been widely explored as a structural modification to the p-donor unit.6,7 The rationale behind the design of TTF derivatives with extended conjugation is twofold: (i) the oxidised states responsible for conduction in charge-transfer complexes and radical cation salts should be stabilised by decreased intramolecular Coulombic repulsion, and (ii) increased spacial extension of the p-framework should lead to increased dimensionality. There is now clear evidence from detailed solution electrochemical studies on several 2,2¾-ethanediylidenebis(1,3-dithiole) derivatives, e.g.the parent system 4a,6a,b that the second oxidation potential is significantly lower than that of TTF 1. The vinylogue 5 of BEDT-TTF 3 was recently synthesised independently and concurrently by three research groups.6c–e Although,to date, donor 5 has not yielded any superconducting salts, a recent report that donor 6a, which comprises a closelyrelated vinylogous TTF framework, affords a superconducting Au(CN)2 salt6h has added a new impetus to studies on these systems,and a 1,3-diselenole analogue 6b has been synthesised.8 Here we describe the synthesis of compound 14, which is the first reported vinylogue of TMTSF 2, along with the X-ray crystal structure and solution electrochemical properties of this new p-electron donor.The synthesis, X-ray crystal structure and electrochemistry of the tetramethyldiselenadithiafulvalene analogue 16 are also reported for the first time. acceptor tetracyano-p-quinodimethane (TCNQ) exhibited met- Results and Discussion allic conductivity.2 Salts of the related p-donor molecule tetramethyltetraselenafulvalene (TMTSF) 2 provided the first Synthesis family of organic superconductors3 and the synthesis of new multi-chalcogen p-electron donors has remained at the fore- The synthesis of 14 is presented in Scheme 1.The key step in assembling the vinylogous TMTSF skeleton is the Wittig front of research, with a few systems, notably bis(ethylenedithio)- tetrathiafulvalene (BEDT-TTF) 3, providing radical cation reaction of aldehyde 13 with the phosphorus ylide derived from reagent 12, for which the starting material was the known salts which are organic superconductors with Tc values as high as ca. 12 K.4 The complex TTF–TCNQ, is considered to be a selone 7.9 Methylation of 7 using methyl trifluoromethanesulfonate yielded the 1,3-diselenolium cation salt 8 which, upon one-dimensional metal, whereas salts of TMTSF 2 and BEDTTTF 3 are characterised by an increase in dimensionality reduction with sodium cyanoborohydride, yielded the unstable selenoether 9.Conversion of compound 9 into the 1,3-diselenol- of their transport properties, arising from close interstack chalcogen···chalcogen interactions. This effect is known to ium cation 10 was achieved by treatment with tetrafluoroboric acid in diethyl ether.Salt 10 was isolated as a very hygroscopic, stabilise the metallic state by suppressing the Peierls distortion, 381 J. Mater. Chem., 1997, 7(3), 381–385382 Scheme 2 Reagents and conditions: i, BuLi, THF, -78 °C, 0.25 h; ii, 13, THF, -78�20 °C, 12 h Fig. 1 Molecular structure of 16; symmetrically related atoms are primed Table 1 Bond lengths from the crystal structures of 14 and 16 bond lengths/A° 14(X=Se) 16(X=Se/S) Scheme 1 Reagents and conditions: i, CF3SO3Me, CH2Cl2, 20°C, 2 h; ii, NaCNBH3, THF, 20 °C, 0.25 h; iii, HBF4, Et2O, 0 °C, 0.5 h; iv, C(1)–X(1) 1.897(3) 1.847(3) PPh3, MeCN, 20 °C, 12 h; v, PBu3, MeCN, 20°C, 0.5 h; vi, Et3N, C(1)–X(2) 1.895(3) 1.848(3) MeCN, 20 °C, 0.25 h; vii, glyoxal (aq), 20 °C, 3 h; viii, KOBut, MeCN, C(1)–C(4) 1.353(4) 1.348(5) 20 °C, then immediately compound 13, 20°C, 0.66 h X(1)–C(3) 1.906(3) 1.865(3) X(2)–C(2) 1.908(3) 1.870(3) C(2)–C(3) 1.342(4) 1.344(5) unstable solid, which was used immediately in the next step.C(4)–C(4¾) 1.437(5) 1.440(7) The overall yield for the three-step sequence 7�10 was typically 70–75%. Cation salt 10, upon reaction with triphenylphosphine or tributylphosphine, yielded the unstable Table 2 Crystal data for 14 and 16 salts 11 and 12, respectively: the former could be isolated as a pink solid, but the latter decomposed rapidly and could not 16 14 be isolated.Therefore, compound 12 was used immediately formula C12H14S2Se2 C12H14Se4 after preparation. Deprotonation of 11 with triethylamine at M 380.3 474.1 0°C gave a transient ylide which was intercepted in situ with a/A° 6.411(1) 6.483(1) aqueous glyoxal to furnish the desired vinylogous aldehyde 13 b/A° 6.837(1) 6.873(1) (70% yield) as a pale yellow solid which could be conveniently c/A° 8.337(1) 8.378(1) stored under an inert atmosphere at 0°C for up to four weeks.a(°) 70.35(1) 70.48(1) The ylide from triphenylphosphine reagent 11 was not suffic- b(°) 81.76(1) 81.67(1) c(°) 82.47(1) 82.44(1) iently activated to react with the conjugated aldehyde group setting reflns 478 512 of 13, so we used the more reactive tributylphosphine analogue h range(°) 10–30 10–30 12, drawing on our experience of 1,3-dithiole Wittig chemis- V /A° 3 339.25(8) 346.75(8) try.10 Thus, sequential addition of potassium tert-butoxide and Dx/g cm-3 1.86 2.27 aldehyde 13 to salt 12 yielded the target compound 14 as an m(Mo-Ka)/cm-1 57.3 105.5 air-stable, bright yellow crystalline solid in 70% yield.crystal size/mm 0.4×0.1×0.06 0.4×0.22×0.14 min./max. transmission 0.338/0.736 0.077/0.325 Similarly, the tetramethyldiselenadithiafulvalene analogue 16 data total 2833 3106 was obtained (78% yield) by deprotonation of 1,3-dithiole data unique 1808 1841 reagent 15 using butyllithium, following the known pro- Rinta 0.080, 0.040 0.122, 0.033 cedure,11 followed by addition of aldehyde 13 (Scheme 2).data observed, |F|>4s(F) 1615 1694 R(F, obs. data) 0.039 0.028 X-Ray molecular structures of 14 and 16 wR(F2, all data) 0.100 0.073 goodness-of-fit 1.23 1.15 The molecular structures of compounds 14 and 16 have been Dr max, min/e A° -3 0.73, -0.67 0.45, -1.16 determined by single crystal X-ray analysis.Crystals of 14 and 16 are isomorphous. Both molecules (Fig. 1, Tables 1 and 2) aBefore and after the absorption correction.J . Mate r . Chem., 1997, 7(3), 381–385 383 Table 3 Cyclic voltammetric data for new vinylogous systems 14 and possess a crystallographic inversion centre and adopt small 16, with selected compounds for comparison.Data are versus Ag/AgCl, chair-like distortions, the dithiole/diselenole rings folding by unless otherwise stated 7.8 (14) and 7.0° (16) along the S(Se)···S(Se) vectors. In 16 the Ci molecular symmetry is spurious, due to disorder, which Compound E11/2/V E21/2/V DE/V makes the S and Se atoms indistinguishable.This observation 1 TTF 0.34 0.71 0.37 has precedent in other mixed sulfur/selenium tetrachalcogeno- TSFa,b 0.48 0.76 0.28 fulvalene derivatives.12 The C(1)NC(4) and C(4)–C(4¾) bond 4ac 0.20 0.36 0.16 distances are similar to thos other planar systems of this 4bc 0.26 0.40 0.14 kind6d,f and indicate a small degree of p-delocalisation (ca. 4cc 0.32 0.47 0.14 10%).13 TMTTFa,c 0.25 0.61 0.36 Molecules in the crystals are arranged in planar layers 2 TMTSFd 0.44 0.72 0.28 4dc 0.19 0.34 0.15 parallel to the crystallographic (10 2) plane (Fig. 2). Molecules 16 0.29 0.44 0.15 within a layer, related via the b translation, form intermolecular 14 0.36 0.50 0.14 chalcogen···chalcogen contacts of 3.87 (in 14) and 3.90 A° (in 16). The latter (effectively, Se···S) distance is slightly longer aTSF=tetraselenafulvalene; TMTTF=tetramethyltetrathiafulvalene.than the sum of the van der Waals radii of selenium (2.0 A° )13 bRef. 16. cRef. 6(b). dRef. 17. Data taken from ref. 16, reported using and sulfur (1.8 A° ),14 while the former (Se···Se) contact is shorter Et4NClO4 in MeCN versus SCE. than the double radius of selenium. It is noteworthy that the substitution of Se for S causes no appreciable expansion of the structure along the y axis [b=6.837(1) A° in 16 vs. 6.873(1) A° in 14, while the difference between the S and Se radii should the following general trends in the redox properties. With have contributed 0.2 A° per unit cell translation]. The effect increasing conjugative length there is (i) a lowering of both can be attributed to the higher atomic polarisability of Se redox potentials (especially E21/2) due to the increased electron compared to S (3.77×10-24 and 2.90×10-24 cm3, respect- delocalisation and (ii) a smaller difference (DE) between E11/2 ively15), which makes the electron shell of the former easier to and E21/2 (tending to zero as the conjugation length increases), deform to maximise the packing density elsewhere, but is also indicative of increased stabilisation of the dicationic state as a favourable for stronger intermolecular interactions.The result of increased charge separation (and thus reduced on-site interplanar separations between the layers are ca. 3.68 (14) Coulombic repulsion). For the series 4d,6b 16 and 14 it is and 3.64 A° (16), with only partial overlap between the noteworthy that the oxidation becomes harder by sequentially molecules.substituting selenium atoms for sulfur whilst DE is essentially unaffected by selenium replacement. These observations are Solution electrochemistry attributable to a decrease in p-orbital interaction between the carbon framework and the heteroatom as a result of increasing The solution redox properties of donors 14 and 16 have been heteroatom size.16 studied by cyclic voltammetry and the results are collated in Table 3, along with selected model compounds for comparison.The new extended compounds are very efficient p-electron Conclusions donors; they display the expected two reversible, one-electron In summary, we have achieved the first synthesis of a vinylogue redox couples.These data are entirely consistent with previous of TMTSF 2, namely 2,2¾-ethanediylidenebis(4,5-dimethyl-2H- work with vinylogous TTF systems,6 which has established 1,3-diselenole) 14. The 1,3-dithiole analogue 16 is also reported. These new compounds are very efficient p-electron donors, and X-ray structural analysis of 14 and 16 reveals that the molecules are arranged in planar layers.This combination of structural and electrochemical properties makes compounds 14 and 16 promising candidates for the formation of conducting or superconducting radical ion salts. Experimental General details Details of equipment and procedures are the same as those reported recently.18 Solvents and reagents employed were standard reagent grade and were used as received unless otherwise stated.All anhydrous solvents were obtained by standard techniques and acid-free CH2Cl2 was prepared by either washing with dilute sodium hydrogen carbonate or filtration through basic alumina, followed by distillation prior to use. Cyclic voltammetric experiments were performed using 10-5 M donor and 0.1 M Bu4NClO4 in dry MeCN under argon Fig. 2 Crystal packing of 14, showing short intermolecular Se···Se versus Ag/AgCl, Pt working and counter electrodes, 20°C, contacts (<4 A°). Symmetrically related atoms are primed; H atoms are omitted. recorded on a BAS 50W electrochemical analyser.384 4,5-Dimethyl-2-methylseleno-1,3-diselenolium (4,5-Dimethyl-2H-1,3-diselenol-2-yl )tributylphosphonium trifluoromethanesulfonate 8 Tetrafluoroborate salt 10 (65 mg, 0.198 mmol) was dissolved To a stirred solution of 4,5-dimethyl-2H-1,3-diselenole-2-selone in dry MeCN (20 cm3) under argon at 20°C and treated with 79 (300 mg, 0.98 mmol) in dry CH2Cl2 (25 cm3) was added freshly distilled tributylphosphine (0.07 cm3, 0.26 mmol).The methyl trifluoromethanesulfonate (0.14 cm3, 1.22 mmol). The orange solution immediately decolorised and was left to stir resultant mixture was stirred under an argon atmosphere for for 0.5 h whereupon it was used directly in the preparation 2 h at 20°C whereupon the volume of the mixture was reduced of 14.to ca. 5 cm3 in vacuo. Addition of anhydrous diethyl ether precipited a solid, which was filtered, washed with diethyl ether 2-(4,5-Dimethyl-2H-1,3-diselenol-2-ylidene)ethanal 13 and dried to give 8 (400 mg, 87%) as an unstable pale yellow To a solution of reagent 11 (260 mg, 0.53 mmol) in MeCN solid, mp 120–121 °C (Calc.for C7H9F3O3SSe3: C, 17.87; H, (20 cm3) was added triethylamine (0.11 cm3, 0.8 mmol) and 1.91. Found: C, 19.19; H, 2.37%); dH (CDCl3) 3.17 (3H, s), 2.67 the mixture was stirred for 15 min at 20°C, whereupon glyoxal (6H, s).(1.0 cm3 of a 40% aqueous solution, excess) was added and the solution stirred at room temperature for 3 h. The mixture 4,5-Dimethyl-2-methylseleno-2H-1,3-diselenole 9 was diluted with water (50 cm3), extracted with CH2Cl2 To a solution of salt 8 (400 mg, 0.86 mmol) in anhydrous THF (2×50 cm3), the organic portions were combined and dried (30 cm3) under argon at 20°C was added sodium cyanoborohy- (MgSO4), and the solvent removed in vacuo.The residue was dride (1 M in THF, 1.07 mol, 1.07 cm3) dropwise over 2 min. purified by column chromatography on neutral alumina, The yellow solution rapidly turned light orange and was initially with CH2Cl2–hexane as eluent (152 v/v) followed by maintained at 20°C for 15 min. At this point, the THF was CH2Cl2, to afford 13 (100 mg, 70%) as a pale yellow solid, mp removed in vacuo and the residue taken up in a mixture of 65–67°C; m/z (80Se, DCI) 269 (MH+, 100%) (HRMS: Calc.diethyl ether (50 cm3) and water (50 cm3). The aqueous phase for C7H8OSe2, 267.8906. Found, 267.9071); dH(CDCl3) 9.46 was separated and washed with diethyl ether (2×50 cm3), the (1H, d, J 1.8), 7.20 (1H, d, J 1.8), 2.17 (3H, s), 2.13 (3H, s); dC organic layers were combined and dried (MgSO4). Removal (CDCl3 ) 182.7, 161.5, 133.0, 126.5, 114.0, 15.7, 15.6; of the solvent in vacuo afforded compound 9 (257 mg, 93%) nmax(KBr)/cm-1 1605 (CNO). as a bright yellow solid (mp 61–63 °C) which was essentially pure by 1H NMR spectroscopy. Correct elemental analysis 2,2¾-Ethanediylidenebis(4,5-dimethyl-2H-1,3-diselenole) 14 could not be obtained due to the rapid decomposition of 9 during handling (with the liberation of methyl selenol) (Calc.To a stirred solution of phosphonium salt 12 in anhydrous for C6H10Se3 : C, 22.59; H, 3.16. Found: C, 24.15; H, 3.00%); MeCN, as prepared above, at 20°C was added potassium tertm/ z (DCI, 80Se) 322 (M+, 5%), 226 (M+-MeSeH, 100); butoxide (22 mg, 0.198 mmol) followed by the immediate dH(CDCl3) 5.9 (1H, s), 2.2 (3H, s), 1.95 (6H, s).addition of an MeCN solution of aldehyde 13 (58 mg, 0.216 mmol). The mixture turned deep orange on addition of 4,5-Dimethyl-1,3-diselenolium tetrafluoroborate 10 the butoxide and then bright yellow with the formation of a white precipitate on addition of the aldehyde. The mixture was To an ice-cooled solution of 9 (240 mg, 0.75 mmol) in anhy- stirred for 40 min and then the solvent was evaporated in drous diethyl ether (20 cm3) was added dropwise over 5 min vacuo to afford a brown residue which was flushed through a tetrafluoroboric acid (0.82 mmol, 0.14 cm3 of a 54% complex column containing a short plug of neutral alumina using acid- in diethyl ether).After 0.5 h, the pink solid which had precipi- free CH2Cl2–hexane mixture (151 v/v) as the eluent, to yield tated was rapidly filtered and washed with dry diethyl ether yellow crystals contaminated with a small amount of an (50 cm3) to afford 10 (217 mg, 89%) as an extremely hygro- unidentified orange oil.After washing this product with diethyl scopic, salmon-pink solid which was used directly in sub- ether, compound 14 (80 mg, 85%) was isolated as bright yellow sequent reactions.crystals, mp 244–245 °C (from CS2) (Calc. for C12H14Se45C, 30.37; H, 2.95. Found: C, 30.22; H, 2.91%); m/z (80Se, DCI) (4,5-Dimethyl-2H-1,3-diselenol-2-yl )triphenylphosphonium 477(M+, 100%); dH(CDCl3 ) 5.95 (2H, s), 1.95 (12H, s); tetrafluoroborate 11 nmax(KBr)/cm-1 1647, 1519, 792; lmax(MeCN)/nm (e) 371 Tetrafluoroborate salt 10 (250 mg, 0.77 mmol) was dissolved (1.9×104).A crystal of 14 suitable for X-ray analysis was in dry MeCN (30 cm3) under argon at 20°C and treated with grown by slow evaporation of a CS2 solution. triphenylphosphine (220 mg, 0.85 mmol). The resultant solution was stirred under argon for 12 h, by which time the 2-[2-(4,5-Dimethyl-2H-1,3-diselenol-2-ylidene)ethylidene]-4,5- solution had turned deep red.The volume of the mixture was dimethyl-2H-1,3-dithiole 16 reduced in vacuo to ca. 2 cm3 before ice-cold anhydrous diethyl To a stirred solution of compound 1511 (35 mg, 0.15 mmol) in ether (50 cm3) was added. The resultant solution was stirred dry THF (20 cm3) under argon at -78 °C was added BuLi at room temperature for 15 min, whereupon an off-white solid (0.1 cm3 of a 1.6 M solution in hexane, 0.16 mmol) and the precipitated.The diethyl ether was decanted off and the solid solution stirred for 15 min. Compound 13 (35 mg, 0.13 mmol) washed rapidly with ice-cold anhydrous diethyl ether in dry THF (5 cm3) was then added and stirring continued at (2×20 cm3). The solid was dried under high vacuum to afford -78°C for 1 h and the reaction mixture was allowed to reach 11 (260 mg, 70%) as a hygroscopic pink solid, mp 46–50 °C; dH(CDCl3) 7.8–7.6 (15H, m), 6.85 (1H, d, J 4.7†), 2.0 (6H, s). 20°C (ca. 15 h). The solvent was evaporated, water (10 cm3) was added and the residue was extracted with CH2Cl2 (acidfree, 3×25 cm3). The combined extracts were washed with † J values given in Hz.J .Mate r . Chem., 1997, 7(3), 381–385 385 Chem. Soc., 1981, 103, 2440; (b) K. Bechgaard and D. Je�rome, Sci. water (2×10 cm3) and dried (MgSO4), and the solvent was Am., 1982, 247, 50. evaporated. Column chromatography of the residue on neutral 4 (a) A. M. Kini, U. Geiser, H. H. Wang, K. D. Carlson, alumina eluting with hexane–toluene (251 v/v) afforded com- J. M. Williams, W.K. Kwok, K. G. Vandervoot, J. E. Thompson, pound 16 (39 mg, 78%) as a yellow solid, mp 242–243 °C D. L. Stupka, D. Jung and M-H. Whangbo, Inorg.Chem., 1990, 29, (from CS2 ) (Calc. for C12H14S2Se2 : C, 37.90; H, 3.71. Found: 2555; (b) J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H. H. Wang, A. M. Kini and M-H. Whangbo, Organic C, 38.13 H, 3.98%); m/z (80Se, DCI) 382 (M+, 100%); Superconductors (including Fullerenes), Prentice Hall, New Jersey, dH[CS2–(CD3)2CO] 6.12 (1H, d, J 10.5), 5.55 (1H, d, J 10.5), 1992. 1.95 (3H, s), 1.94 (3H, s), 1.90 (3H, s), 1.89 (3H, s); 5 S. Roth, One-Dimensional Metals, VCH, Weinheim, 1995. nmax(KBr)/cm-1 1630, 1501; lmax(MeCN)/nm (e) 393 6 (a) Z. Yoshida, T. Kawasi, H. Awaji, I. Sugimoto, T. Sugimoto and (1.8×104).A crystal suitable for X-ray analysis was grown by S. Yoneda, T etrahedron L ett., 1983, 24, 3469; (b) T. Sugimoto, H. Awaji, I. Sugimoto, Y. Misaki, T. Kawase, S. Yoneda and slow evaporation of a CS2–hexane solution. Z. Yoshida, Chem. Mater., 1989, 1, 535; (c) V. Yu Khodorkovskii, L. N. Veselova and O. Ya. Neiland, Khim. Geterotsikl. Soedin., 1990, 130 (Chem. Abstr., 1990, 113, 22868); (d) A.J. Moore, M. R. X-Ray crystallography Bryce, D. J. Ando and M. B. Hursthouse, J. Chem. Soc., Chem. Commun., 1991, 320; (e) T. K. Hansen, M. V. Lakshimikantham, Single-crystal diffraction experiments were carried out at T= M. P. Cava, R. M. Metzger and J. Becher, J. Org. Chem., 1991, 56, 150 K on a Siemens 3-circle diffractometer with a CCD area 2720; (f ) M.R. Bryce, M. A. Coffin and W. Clegg, J. Org. Chem., detector, using graphite monochromated Mo-Ka radiation 1992, 57, 1696;(g)M.Salle�,M.Jubault, A. Gorgues, K. Boubekeur, (l=0.71073 A° ). The yellow plate-like crystals of 14 and 16 M. Fourmigue�, P. Batail and E. Canadell, Chem. Mater., 1993, 5, were isomorphous, in triclinic space group P1� (No. 2), Z=1. 1196; (h) Y. Misaki, N.Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and S. Tanaka, Angew. Chem., Int. Ed. Engl., 1995, 34, A hemisphere of data with 2h 61° were collected in an v 1222; (i ) Y. Misaki, T. Ohta, N. Higuchi, H. Fujiwara, T. Yamabe, scan mode (0.3° steps) and corrected for absorption using the T. Mori, H. Mori and S. Tanaka, J. Mater. Chem., 1995, 5, 1571; Gaussian integration technique for the real crystal shape (8 ( j) D.Lorcy, R. Carlier, A. Robert, A. Tallec, P. Le Magueres and and 6 faces indexed, respectively). The structures were solved L. Ouahab, J. Org. Chem., 1995, 60, 1443; (k) M. R. Bryce, by direct methods and refined by full-matrix least-squares A. J. Moore, B. K. Tanner, R. Whitehead, W. Clegg, F. Gerson, A. Lamprecht and S. Pfenninger, Chem.Mater., 1996, 8, 1182.(non-H atoms with anisotropic displacement parameters; the 7 For reviews on vinylogous TTF donors see: (a) Z. Yoshida and disordered Se/S atoms in 16 were refined at common sites with T. Sugimoto, Angew. Chem., Int. Ed. Engl., 1988, 27, 1573; 0.5/0.5 occupancies; all H atoms refined in isotropic approxi- (b) M. R. Bryce, J. Mater. Chem., 1995, 5, 1481. mation; 101 variables) against F2 of all data, using SHELXTL 8 Y.Misaki, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and software.19 Crystal data and experimental details are listed S. Tanaka, Chem. Commun., 1996, 363. 9 K. Bechgaard, D. O. Cowan, A. N. Bloch and L. Henriksen, J. Org. in Table 2. Chem., 1975, 40, 746. Atomic coordinates, thermal parameters, and bond lengths 10 A. J. Moore and M.R. Bryce, unpublished observations. See also and angles have been deposited at the Cambridge references 6(a) and 6(b) in which tributylphosphine is used exclus- Crystallographic Data Centre (CCDC). See Information for ively in similar reactions. Authors, J. Mater. Chem., 1997, Issue 1. Any request to the 11 K. Akiba, K. Ishikawa and N. Inamoto, Bull. Chem. Soc. Jpn., 1978, 51, 2674; A.J. Moore and M. R. Bryce, J. Chem. Soc., Perkin CCDC for this material should quote the full literature citation T rans. 1, 1991, 157. and the reference number 11451/24. 12 (a) A. Mhanni, L. Ouahab, D. Grandjean, J. Amouroux and J. M. Fabre, Acta Crystallogr., Sect. C, 1991, 47, 1980; (b) S. Triki, L. Quahab, D. Grandjean, J. Amouroux and J. M. Fabre, Acta We thank EPSRC for funding this work.Crystallogr., Sect. C, 1991, 47, 1941. 13 L. Pauling, T he Nature of the Chemical Bond, 3rd edn., Cornell University Press, Ithaca, 1960. 14 G. Filippini and A. Gavezzotti, Acta Crystallogr., Sect. B, 1993, References 49, 868. 1 (a) J. R. Ferraro and J. M. Williams, Introduction to Synthetic 15 T. Miller and B. Bedeson, Adv. Atom. Mol. Phys., 1977, 13, 1. Electrical Conductors, Academic Press, London, 1987; 16 E. M. Engler, F. B. Kaufman, D. C. Green, C. E. Klots and R. N. (b) M. R. Bryce, Chem. Soc. Rev., 1991, 20, 355; (c) A. E. Underhill, Compton, J. Am. Chem. Soc., 1975, 97, 2921. 17 E. M. Engler, V. V. Patel, J. R. Anderson, R. R. Schumaker and J. Mater. Chem., 1992, 2, 1; (d) J. Mater. Chem., Special Issue on A. A. Fukushima, J. Am. Chem. Soc., 1978, 100, 3769. Molecular Conductors, 1995, 5, 1469. 18 General details: M.R. Bryce, A. Chesney, A. K. Lay, A. S.Batsanov 2 (a) J. P. Ferraris, D. Cowan, V. Walatka anPerlstein, J. Am. and J. A. K. Howard, J. Chem. Soc., Perkin T rans. 1, 1996, 2451. Chem. Soc., 1973, 95, 948; (b) L. B. Coleman, M. J. Cohen, 19 G. M Sheldrick, SHELXTL, ver. 5/VMS, Siemens Analytical X- D. J. Sandman, F. G. Yamagishi, A. F. Garito and A. J. Heeger, Ray Instruments Inc., Madison, Wisconsin, USA, 1995. Solid State Commun., 1973, 12, 1125. 3 (a) K. Bechgaard, K. Carneiro, F. B. Rasmussen, M. Olsen, G. Rindorf, C. S. Jacobsen, H. J. Pedersen and J. C. Scott, J. Am. Paper 6/06834K; Received 7th October, 1996

ISSN:0959-9428    

DOI:10.1039/a606834k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Preparation and X-ray crystal structures of the first radical cation salts of 4-iodotetrathiafulvalene: [ITTF .+]2 {Pd[S2C2(CN)2]2}2- and ITTF .+HSO4- Andrei S. Batsanov,a Adrian J. Moore,a Neil Robertson,b Andrew Green,a Martin R. Bryce,*a Judith A. K. Howarda and Allan E. Underhill*b aDepartment of Chemistry, University of Durham, Durham, UK DH1 3L E bDepartment of Chemistry, UCNW Bangor, Bangor, Gwynedd, UK L L 57 2UW The title radical ion salts of 4-iodotetrathiafulvalene 1 have been prepared and their X-ray crystal structures determined at 150 K.The 251 salt [ITTF.+]2 {Pd[S2C2(CN)2 ]2}2- 3 forms a mixed stack structure in which the Pd(mnt)2 anions intermingle with pairs of iodo-TTF radical cations, i.e. a DDADDA stacking arrangement. The structure of the 151 salt ITTF.+ HSO4- 4 comprises stepped stacks of ITTF cations with two alternating modes of overlap.Between the cation stacks there are infinite chains of hydrogensulfate anions, linked by hydrogen bonds. Both structures are characterised by short intermolecular contacts involving the iodine substituent. Within the field of molecular conductors,1 the control of a perchlorate salt by electrocrystallisation in acetonitrile in the presence of tetrabutylammonium perchlorate as supporting intermolecular interactions in the solid state by chemical modification is a challenging topic, and the pivotal role played electrolyte.In these experiments the HSO4- anion must be derived from residual sulfuric acid which had been used for by chalcogen atoms is well established.It is widely recognised within solid-state chemistry that halogen atoms can participate washing the electrodes prior to the electrocrystallisation. in relatively strong and directional intermolecular interactions, thereby providing an effective means of ‘crystal engineering’.2 In this context, halogenated derivatives of tetrathiafulvalene (TTF), ethylenedithio-TTF (EDT-TTF) and ethylenedithiodiselenadithiafulvalene (EDT-DSDTF) are emerging as new p-electron donors in the search for TTF-based radical cation salts and charge-transfer complexes which possess increased dimensionality.3 Although a range of halogenated derivatives of TTF have been synthesised in several laboratories,4 to date, only one radical cation salt has been well characterised, viz.an insulating 151 iodide salt of tetraiodo-TTF, the X-ray crystal structure of which has been reported recently.4e The X-ray crystal structures of a few radical ion salts of halogenated EDT-TTF and EDT-DSDTF derivatives are known,5 and some are molecular semiconductors {e.g.a [Pd(dmit)2]5a and a ClO4 salt}5c and these structures are characterised by relatively strong interactions between the halogen substituent and the anions.It is known that halogenation of the TTF skeleton raises the oxidation potential significantly4 (as would be expected The asymmetric unit of the crystal structure of salt 3 for the attachment of electron-withdrawing substituents). comprises one ITTF.+ radical cation (in a general position) Therefore, we directed our attention to monohalogeno-TTFs,4b and a half of a [Pd(mnt)2]2- anion located at an inversion and we considered iodine to be the most promising substituent centre (Fig. 1, Table 1); both moieties are nearly planar. The for participating in intermolecular interactions, as it is more polarisable than the other halogens. Herein we report the preparation and X-ray crystal structures of the first radical cation salts of 4-iodo-TTF 1.Results and Discussion 4-Iodo-TTF 1 was synthesised by halogenation of 4-tetrathiafulvalenyllithium using perfluorohexyl iodide, as reported by Becker et al.4c This halogenating reagent is more efficient than tosyl iodide which we had used previously.4b The 251 salt [ITTF.+]2 {Pd[S2C2(CN)2]2}2- 3 was obtained as black crystals by mixing compound 1 and K+{Pd[S2C2(CN)2]2}- 2 in acetone.The 151 salt ITTF.+HSO4- 4 was obtained by electrochemical oxidation of donor 1 under constant current in acetonitrile containing sulfuric acid. Remarkably, the same Fig. 1 ITTF and Pd(mnt)2 ions in the crystal structure of 3, projected on their planes hydrogensulfate salt 4 was obtained during attempts to obtain J. Mater. Chem., 1997, 7(3), 387–389 387Table 1 Selected bond distances (A° ) in the structures of 3 and 4 3 3 4 PdMS(5) 2.302(4) C(1)MC(4) 1.38(2) 1.392(7) PdMS(6) 2.288(4) C(1)MS(1) 1.72(1) 1.731(5) S(5)MC(7) 1.72(2) C(1)MS(2) 1.74(2) 1.735(5) S(6)MC(8) 1.73(2) S(1)MC(2) 1.77(2) 1.738(5) C(7)MC(8) 1.39(2) S(2)MC(3) 1.73(2) 1.735(5) 4 C(2)MC(3) 1.35(2) 1.344(7) S(5)MO(1) 1.443(4) C(2)MI 2.06(2) 2.083(5) S(5)MO(2) 1.519(4) C(4)MS(3) 1.72(2) 1.723(5) S(5)MO(3) 1.521(3) C(4)MS(4) 1.737(14) 1.724(5) S(5)MO(4) 1.444(3) S(3)MC(5) 1.74(2) 1.724(5) C(5)MC(6) 1.34(2) 1.337(8) Fig. 4 Crystal structure of 4, showing hydrogen bonds (dashes), the radical cations form a dimer with an interplanar separation of disorder of the H atom in the O(2)HO(2¾) bond, and short 3.4 A° . These dimers intermingle with [Pd(mnt)2]2- anions to contacts (dots) form a mixed DDADDA stack parallel to the [1 1� 0] crystallographic direction (Fig. 2). The cation and anion planes in the stack form a dihedral angle of 9° with an average interplanar separation of 3.6 A° . Short contacts (S,S 3.67–3.73 A° and S,I cations form a stair-like stack with two alternating kinds of 3.81 A° ) between cations and anions of different stacks join the overlap: (i) between two TTF moieties with a lateral shift of stacks into layers parallel to the (0 0 1) plane (Fig. 3). A nearly ca. 0.5 A° , and (ii) between substituted dithiole rings only; the linear CMI,NMC interlayer contact [I,N(2) 3.04 A° ] is interplanar separations are 3.33 and 3.40 A° , respectively. remarkably shorter than the sum of van der Waals radii Parallel to this stack, i.e.in the direction of the crystallographic (3.65 A° ),6 even after the correction for asphericity of the iodine axis y, runs a chain of hydrogensulfate anions, linked by strong atom (3.36 A° ).7 hydrogen bonds O(2),O(2¾) 2.555(7) and O(3),O(3¾) The asymmetric unit of salt 4 comprises an ITTF.+ radical 2.627(7) A° . Both of these bonds are crystallographically centro- cation and a HSO4- anion (Fig. 4, Table 1). Almost planar symmeric. In the former bond the hydrogen atom was found to be disordered over two positions, corresponding to (asymmetric) distances OMH 0.8(1) and H,O 1.9(1) A° . In the latter bond the only peak of electron density was located at the inversion centre, implying a truly symmetrical bond. Although both H atoms were successfully refined, the reliability of this result is limited.The anion–cation contacts I,O(4) 2.92 (CMIMO 168°) and S(3),O(2) 2.82 A° are substantially shorter than the sums of the van der Waals radii (3.5 and 3.2 A° , or if corrected for ellipsoidal shape of the I and S atoms, 3.16 and 3.00 A° , respectively),6,7 and imply significant polarisation of the ‘soft’ I or S atoms. On the other hand, the H(3),O(1) and H(6),O(1) contacts of 2.19(5) and 2.24(6) A° can be regarded as hydrogen bonds.Thus, the anionic chain contributes significantly to the close packing of cations. The geometry of the ITTF moieties in 3 and 4 clearly characterises them as radical cations. The elongation of the central CNC bond distance is usually the most sensitive indicator of the degree of charge transfer.These bonds in 3 [1.38(2) A° ] and 4 [1.392(7) A° ] are significantly longer than in neutral 1 [1.34(1) A° ]4c and in two polymorphs of pure TTF [1.349(3)8a and 1.337(4)8b A° ]. They are also marginally longer than in radical cation salts with ‘soft’ anions, such as I4TTF.+I- [1.369(4) A° ],4e and close to the distances in the salts with strongly electronegative counter ions and complete charge Fig. 2 Stack of ions in the structure of 3 transfer (1.39–1.40 A° ).9 A linear relation b=1.757-0.0385d has been suggested recently10 between the mean length (b) of the four CMS bonds adjacent to the central CNC bond and the degree of charge transfer d. For b=1.730(8) A° in 3 a 1.728(5) A° in 4, this formula gives d=0.7(2) and 0.75(13), respectively.Both salts 3 and 4 exhibit low conductivity values [srt= 2×10-6 S cm-1 (four-probe compressed pellet measurement) and 5×10-7 S cm-1 (two-probe, single-crystal measurement) respectively]. Preliminary static susceptibility data on a small polycrystalline sample of salt 3 over the temperature range 300–4 K suggest that the material behaves as a one-dimensional Heisenberg antiferromagnet with an isotropic nearest neighbour exchange interaction, J#50 K, consistent with the Bonner–Fischer model.11 These magnetic data are qualitatively similar to those of many linear chain charge-transfer com- Fig. 3 Interstack contacts in the structure of 3; projection on the (1 1� 0) plane pounds studied previously,12 including the salt I4TTF.+ I-.4e 388 J. Mater. Chem., 1997, 7(3), 387–389Table 2 Crystal data Conclusions compound 3 4 The first radical ion salts of the electron donor molecule ITTF formula C20H6I2N4PdS12 C6H4IO4S5 1 have been prepared, and the X-ray crystal structures of the M 1047.21 427.29 title salts establish that the iodine substituent participates to a symmetry triclinic triclinic significant extent in intermolecular interactions.These results, a/A° 7.667(1) 8.145(1) combined with those recently obtained by other workers,4e,5a–c b/A° 8.577(1) 8.242(1) c/A° 11.638(2) 9.916(1) auger well for the use of halogenated TTF derivatives in the a/degrees 74.42(1) 99.17(1) synthesis of new charge-transfer materials, in which the solid b/degrees 88.38(1) 100.98(1) state structure can be modified by intermolecular and c/degrees 86.64(1) 104.75(1) interstack interactions involving polarisable halogen atoms.U/A° 3 735.9(2) 616.5(1) space group P 1� P 1� Z 1 2 Experimental m/cm-1 36.0 34.4 Dc/g cm-3 2.36 2.30 Preparation of [ITTF·+]2 {Pd[S2C2(CN)2]2}2- 3 crystal size/mm 0.02×0.2×0.25 0.11×0.2×0.3 2hmax/degrees 50.5 51 Method 1. 4-Iodo-TTF 14c (7 mg, 0.021 mmol) and data total 3126 2718 K+{Pd[S2C2(CN)2]2}- 2 (15 mg, 0.035 mmol) were each data unique 2227 1948 dissolved in separate portions of dry acetone (10 ml) and data observed, I>2s(I) 1745 1909 placed in the outer compartments of a three-compartment Rinta 0.101, 0.060 0.092, 0.027 transmission min, max 0.67, 1.00 0.46, 0.85 diffusion cell.The central section was filled with dry acetone no. of variables 178 162 (10 ml) and separated from the outer compartments by porous wR(F2), all data 0.223 0.081 glass frits.After 13 days, black crystals of complex 3 (2 mg, goodness-of-fit 1.56 1.12 18%) suitable for X-ray analysis were collected from the central R(F), obs. data 0.078 0.029 compartment and washed with acetone. Drmax/e A° -3 2.4 0.79 Drmin/e A° -3 -2.2 -1.03 Method 2. 4-Iodo-TTF 1 (13 mg, 0.038 mmol) and aBefore and after the absorption correction.K[Pd(mnt)2] (28 mg, 0.068 mmol) were each dissolved in dry acetone (10 ml) and the solutions mixed, affording immediately We thank the EPSRC for funding this work and Dr T. Rogers a black precipitate which was collected by filtration, washed for the magnetic data on salt 4. with cold acetone and dried to afford complex 3 (8 mg, 40%) as a fine black powder.Analysis: found C, 22.80; H, 0.90; N, References 5.38; S, 36.51; C20H6I2N4PdS12 requires C, 22.84; H, 0.57; N, 1 Reviews: (a) M. R. Bryce, Chem. Soc. Rev., 1991, 20, 355; (b) A. E. 5.35; S, 36.71%. Underhill, J. Mater. Chem., 1992, 2, 1; (c) J. Mater. Chem., Special Issue on Molecular Conductors, 1995, 5(10), 1469–1760. 2 G. R. Desiraju, Crystal Engineering, T he Design of Organic Solids, Preparation of ITTF·+HSO4- 4 Elsevier, Amsterdam, 1989, ch. 6. 3 For reviews which focus on increased dimensionality in TTF mate- 4-Iodo-TTF 1 (11 mg, 0.033 mmol) was dissolved in dry, rials, see: (a)M. Adam and K. Mu�llen, Adv.Mater., 1994, 6, 439; (b) degassed acetonitrile (25 ml) containing 0.02 ml of concen- M. R. Bryce, J.Mater. Chem., 1995, 5, 1481.trated sulfuric acid and placed in the anode compartment of a 4 For leading references, see: (a) M. Jorgensen and K. Bechgaard, 50 ml H-shaped electrocrystallisation cell. In the cathode com- Synthesis, 1989, 207; (b) M. R. Bryce and G. Cooke, Synthesis, partment, separated from the anode compartment by a porous 1991, 263; (c) C. Wang, A. Ellern, V. Khodorkovsky, J.Bernstein glass frit, was placed dry, degassed acetonitrile (25 ml) contain- and J. Y. Becker, J. Chem. Soc., Chem. Commun., 1994, 983; (d) C. Wang, J. Y. Becker, J. Bernstein, A. Ellern and ing 0.02 ml of concentrated sulfuric acid. A constant current V. Khodorkovsky, J.Mater. Chem., 1995, 5, 1559; (e) R. Gompper, of 1 mA was passed through the cell for 10 days. Black crystals J. Hock, K.Polborn, E. Dormann and H. Winter, Adv. Mater., of complex 4 (10 mg, 71%) were harvested from the anode, 1995, 7, 41. and were also collected from the walls of the anode compart- 5 (a) T. Imakubo, H. Sawa and R. Kato, J. Chem. Soc., Chem. ment. Analysis: found C, 17.01; H, 0.85; S, 35.32; C20H6N4S12I2 Commun., 1995, 1097; (b) T. Imakubo, H. Sawa and R. Kato, J. Chem. Soc., Chem. Commun., 1995, 1667; (c)M.Iyoda, H. Suzuki, requires C, 16.86; H, 0.94; S, 37.47%. S. Sasaki, H. Yoshino, K. Kikuchi, K. Saito, I. Ikemoto, H. Matsuyama and T. Mori, J.Mater. Chem., 1996, 6, 501. X-Ray crystallography 6 A. Gavezzotti, J. Am. Chem. Soc., 1983, 105, 5220. 7 S. C. Nyburg and C. H. Faerman, Acta Crystallogr., Sect. B, 1985, Single-crystal X-ray diffraction experiments for 3 and 4 41, 274. 8 (a)W. F. Cooper, J. W. Edmonds, F.Wudl and P. Coppens, Cryst. were carried out at T=150 K on a Siemens three-circle Struct. Commun., 1974,3, 23; (b) A. Ellern, J. Bernstein, J. Y. Becker, diffractometer, equipped with a CCD area detector (graphite- S. Zamir, L. Shahal and S. Cohen, Chem.Mater., 1994, 6, 1378. monochromated Mo-Ka radiation, l=0.71073 A° , v-scan 9 (a) P.Batail, C. Livage, S. S. P. Parkin, C. Coulon, J. D. Martin mode, semi-empirical absorption correction on Laue equiva- and E. Canadell, Angew. Chem., Int. Ed. Engl., 1991, 30, 1498; (b) lents) and an Oxford Cryosystems open-flow N2 gas cryostat. P. Erk, S. Hu�nig, G. Klebe, M. Krebs and J. U. von Schu�tz, Chem. The structures were solved by Patterson (3) and direct (4) Ber., 1991, 124, 2005; (c) G.Matsubayashi, K. Ueyama and T. Tanaka, J. Chem. Soc., Dalton T rans., 1985, 465; (d) methods and refined by full-matrix least squares against F2 of T. Iamakubo, H. Sawa and R. Kato, J. Chem. Soc., Chem. all data, using SHELXTL software.13 Non-H atoms were Commun., 1995, 1097. refined anisotropically; all H atoms in 4 were refined in 10 D. A. Clemente and A. Marzotto, J. Mater. Chem., 1996, 6, 941. isotropic approximation, in 3 were treated as ‘riding’. Crystal 11 J. C. Bonner and M. E. Fischer, Phys. Rev. A, 1964, 135, 640. data and experimental details are listed in Table 2; atomic 12 (a) J. B. Torrance in L ow-Dimensional Conductors and Superconductors, ed. D. Je�rome and L. G. Caron, NAT O ASI Ser. coordinates, thermal parameters and bond lengths and angles B, 1987, 165, 113; (b) S. D. Obertelli, R. H. Friend, D. R. Talham, have been deposited at the Cambridge Crystallographic Data M. Kurmoo and P. Day, J. Phys., Condens. Matter, 1989, 1, 5671. Centre (CCDC). See Information for Authors, J. Mater. Chem., 13 G. M. Sheldrick, SHELXTL, Version 5, Siemens Analytical X-Ray 1997, Issue 1. Any request to the CCDC for this material Instruments Inc., Madison, WI, USA, 1995. should quote the full literature citation and the reference number 1145/27. Paper 6/06829D; Received 7th October, 1996 J. Mater. Chem., 1997, 7(3), 387

ISSN:0959-9428    

DOI:10.1039/a606829d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

The azulene ring as a structural element in liquid crystals Sia�n E. Estdale, Roger Brettle, David A. Dunmur and Charles M. Marson Department of Chemistry, University of Sheffield, Sheffield, UK S3 7HF A new approach to the synthesis of azulene liquid crystals is described based on Hafner’s procedure involving reaction of a pyridinium salt with a cyclopentadienide. The preparation of a variety of liquid crystalline materials using this method is described.Variants are reported with single substituents on the azulene ring in the 6-position and doubly substituted in the 2, 6- positions. The effect of the azulene ring as a core or dipolar terminal structural element is explored. 6-(5-Alkyl-1,3-dioxan-2- yl)azulenes are shown to exhibit smectic A phases and 2-cyclohexyl-6-(5-tridecyl-1,3-dioxan-2-yl)azulene show smectic A and B phases.Phase characterisation of the materials is recorded together with X-ray measurements on the smectic A phase of one representative compound. Results of dichroism studies on the azulene mesogens are also briefly reviewed. The essential structure of a calamitic mesogen incorporates a Simple alkyl propane-1,3-diols were prepared by reacting rigid core with a flexible terminal chain, and often a polar end diethyl malonate with the appropriate alkyl halide and then group, and mesophase behaviour is strongly dependent on the reducing the ester groups with LiAlH4; 2-(4-alkyloxyphenyl)- nature of the core.In the search for new mesogenic structures, propane-1,3-diols were prepared by reacting ethyl 4-alkoxythe azulene ring system potentially opens up a whole new phenylacetates with diethyl oxalate; the product was then range of liquid crystal types.The azulene ring C10H10 is a non- decarbonylated and reduced with LiAlH4. benzenoid aromatic hydrocarbon with an intrinsic dipole The products derived from Scheme 1 were a mixture of cis moment (1.08 D) which is delocalised over the whole ring.1 and trans isomers which were separable by MPLC or HPLC, Azulenes are chromophores: the deep blue colour of the parent and were assigned by the characteristic 1H NMR spectra for compound arises from the electronic transitionfrom the highest the two CH2 groups on the dioxan-2-yl ring.For the cis- occupied molecular orbital to the lowest unoccupied antibond- isomers, the chemical shift difference between the axial and ing orbital (the 1Lb band).2 The azulene ring system is planar equatorial hydrogens is small whereas a large chemical shift and thermodynamically stable, although the 10p electrons difference is observed for the trans isomers and this character- display the reactivity expected of an aromatic system.istic pattern agrees with previously published results.12 Substitution of the ring can alter the wavelength of this absorption band resulting in different colours for different azulene derivatives.Praefcke and Schmidt3 reported the synthesis of substituted azulenes linked to nematogenic alkylcyclohexanes by an ester group following the Nozoe procedure.4 We have also used this Attempts were also made to prepare mesogenic azulenes route to produce mesogenic azulenes5 with alkylbiphenyls as with a phenyl ring instead of the dioxan-2-yl ring.Two the mesogenic moiety. In 1990, a series of patents by Mitsubishi homologues 2a,b were prepared by different methods. described the synthesis of a range of 2-substituted,6 6-substi- Deprotection of 1a with dilute hydrochloric acid gives azulene- tuted7 and 2,6-disubstituted azulenes8–10 using the Nozoe route, 6-carbaldehyde which was reacted with the appropriate some of which were mesogenic.Only limited data were pre- Wadsworth–Emmons reagent to give 6-(4-hexyloxystryryl)- sented on the mesophase behaviour of these compounds which azulene, which rapidly decomposed. Reduction of the double were mostly examined as solutes in a nematic host material.bond gave 2a. The C10 analogue, 2b was prepared by reducing The mesophase properties of previously reported azulene based the double bond of the appropriate stilbazole, quaternising the liquid crystals are summarised in Table 1. product with 1-bromobutane and reacting the resulting pyridinium salt with sodium cyclopentadienide. Synthesis In order to prepare potentially mesogenic azulenes without ester linkages, we adopted the Hafner synthesis11 where an N- Mesophase Behaviour alkyl-4-methylpyridinium salt was reacted with sodium cyclo- Of the compounds synthesised, the trans isomers of 1e–k, 1n pentadienide to give 6-methylazulene (see Schemes 1 and 2).and 1p were mesogenic. Table 2 shows the transition tempera- In a similar way we prepared 6-(diethoxymethyl)azulene 1a tures for compounds 1e–k which showed a monotropic smectic by reaction of sodium cyclopentadienide with 4-(diethoxy- A phase.These trans isomers exhibited two crystal forms (K1 methyl)pyridinium bromide. Alternatively, reaction with and K2) which melted at different temperatures. The observed monosubstituted sodium cyclopentadienides gave a mixture of phase sequence is shown in Fig. 1 and illustrates the trends in 1,6- and 2,6-disubstituted azulenes which, in some cases, were melting points of the two crystal forms and the SA phase. (For separable by HPLC. Transacetalation of the diethoxymethyl the two metastable crystal states:K1 corresponds to the melting group with 2-substituted propane-1,3-diols then gave substituted azulenes, some of which were mesogenic.point on initially heating the crystal from room temperature, J. Mater. Chem., 1997, 7(3), 391–401 391Table 1 Transition temperatures and wavelengths of visible absorption of mesogenic azulenes previously reported in the literature transition tempa/°C R1 R2 R3 R4 lmax/nm K N I ref. H CO2Et CO2Et $ 136 $ (110.5) $ 3 H CO2Me CO2Me $ 149 $ (121.9) $ 3 H CO2Et CO2Et 480 $ 123.7 $ (115.9) $ 3 H CO2Pr CO2Pr $ 104.5 $ (89.3) $ 3 H CO2Et H 510 $ 86.1 $ 153.2 $ 3 H CO2Et CO2Et $ 144 $ (78.6) $ 5 H CO2Et H $ 146 $ (145) $ 5 CO2Et CO2Et 475 $ 122 $ (111) $ 8 H H H 476 $ 118 $ (122.6) $ 7 H H H 566 $ 106.7 $ 119.4 $ 7 aParentheses indicate a monotropic transition. and K2 is the melting point when heating the crystal phase calculated to be 27 A° .Molecular modelling calculations were then made in an attempt to describe the molecular arrange- formed on cooling). For compounds where K2 is lower than the monotropic smectic A transition temperature an enanti- ment. At 0 K, the molecular length was determined from MACROMODELto be 27.56 A°, which is close to the observed otropic SA phase is observed.The trans isomer of 1n showed a crystal B phase at around value for the inter-layer spacing of this smectic A phase. An even closer value is obtained when part of the molecule is 170 °C and was identified by the lancet texture observed on cooling from the isotropic phase. For compound 1p, where the tilted with respect to the smectic layers; this has the effect of shorteningthe apparent length of the molecule and calculations 2-substituent is an unsubstituted cyclohexyl ring, smectic A (144 °C) and smectic hexatic B (117°C) phases were observed.predict a value of 26.9 A° at 300 K. However, modelling the molecule at 357 K, the value for the molecular length decreases Compound 1q was prepared as it was hoped that the molecular length could then be extended with a collinear chain on the to 23.65 A°.The entropy of the system is now greater, and this manifests itself in thermal agitation of the alkyl chain which is cyclohexyl ring; however the cis and trans isomers were inseparable by HPLC. no longer fully extended. From this result it is possible to rule out a monolayer structure for this SA phase, since for the Addition of a 2-cyclohexyl substituent (compound 1p) increases the thermal stability of the SA phase compared to temperatures at which the phase is observed, there will be some thermal agitation of the alkyl chain, and the measured the singly substituted 6-(tridecyl-1,3-dioxan-2-yl)azulene, 1h which showed a monotropic smectic A phase, such that an molecular length must be less than the calculated value with a fully extended chain.enantiotropic phase is now observed. This molecule inrporates an aromatic ring with saturated cyclic groups either side In considering how the molecules are arranged within the layers, the intermolecular interactions must also be considered. of it, which traditionally has been considered unfavourable for mesogenic behaviour. Potentially, this molecule opens up a Azulene has a distributed dipole moment and dipolar resonance forms of azulene will contribute to the intermolecular new series of mesogens and it is expected that the addition of a terminal alkyl chain on to the cyclohexyl ring will lower the interactions in the smectic mesophase. It has been reported in the literature13,14 that only anti-azulenophanes of the type clearing points and transition temperatures of the observed mesophases. shown (Fig. 2) can be formed, since this minimises the energy of both the resonance and electrostatic interactions between Small angle X-ray measurements were made for compound 1f, 6-(5-undecyl-1,3-dioxan-2-yl)azulene. From the data the interacting azulene pairs. For the corresponding synazulenophase these interactions would be repulsive.It is obtained, an average value for the inter-layer spacing was 392 J. Mater. Chem., 1997, 7(3), 391–401that involves extensive interdigitation of the alkyl chains, which accounts for both the dipolar interactions of the azulene ring and the thermal disorder of the alkyl chains. Linear Dichroism Since azulene derivatives are coloured, their use as dichroic materials in liquid crystal devices is of some interest.Measurement of the linear dichroism of a number of nonmesogenic and mesogenic compounds dissolved in suitable nematic host materials have been reported.16 Measurements were also carried out on three compounds prepared in this work. From these studies it is possible to determine the degree of order of the host azulene molecules and the angle made by the transition moment to the long molecular axis. For the parent azulene, the transition moment responsible for the characteristic blue colour is polarized perpendicular to the axis2 through carbon atoms 2 and 6.Substitution of the azulene ring and attachment of different terminal groups change the absorption frequency and the angle of the transition moment with respect to the molecular axis.Consequently, it is possible to make azulene liquid crystal mixtures having different colours and with either positive or negative linear dichroism. In Table 3 absorption frequencies and dichroic ratios are summarised for a range of azulene derivatives: a dichroic ratio of less than one indicates that the optical absorption perpendicular to the azulene molecular axis is larger than along the axis.Conclusions New 6-substituted azulenes were successfully synthesised by reacting functionalised N-alkylpyridinium salts with sodium cyclopentadienide to give mesogenic azulenes where the azulene ring was incorporated as an end group. The preparation of 6-(diethoxymethyl)azulene 1a and azulene-6-carbaldehyde was significant as they are functionalised azulenes which may be reacted further to give new 6-substituted azulene compounds.The development of the transacetalation reaction of 6-(diethoxymethyl)azulene led to a new homologous series of mesogenic azulenes which exhibited monotropic smectic A phases in the range 78 to 86°C. These compounds are the first reported azulenes to show a smectic phase. In these compounds it may be argued that the azulene ring has a dual role, and is behaving both as part of the core and as a polar end group.Scheme 1 Molecular modelling substantiated the claim that the dipolar interactions of adjacent azulene rings are important in determining the intermolecular interactions which results in the observed smectic A layered structure, with the alkyl chains extensively interdigitated. Attempts to extend the core led to the synthesis of 6-[5-(4- dodecyloxyphenyl)-1,3-dioxan-2-yl]azulene, 1n.A crystal B phase was observed in the range 170–190 °C. This contrasts with related compounds without a phenyl group as part of the core, which form a smectic A phase approximately 100 °C lower. It was also possible to prepare potential azulene mesogens by hydrogenation of a stilbazole and reacting the quarternised salt with sodium cyclopentadienide. Unfortunately, the resultant 6-(4-decyloxyphenethyl)azulene, 2b was not mesogenic, which can be attributed to the separation of the N H O N O O N O O OH OH Bu + O O Br– – Na+ 1b aromatic rings by a flexible dimethylene linkage.(However, Scheme 2 the intermediate 4-(4¾-decyloxyphenethyl)pyridine was mesogenic, and exhibited a smecticA phase in the range 159–222°C.) New 1,6- and 2,6-disubstituted azulenes were synthesised by expected that in the observed mesophase the azulene rings would adopt a packing arrangement which minimises the the reaction of functionalised N-alkylpyridinum salts with sodium monosubstituted cyclopentadienides.The synthesis of energy of these types of interactions, resulting in an antiparallel bilayer structure as illustrated (Fig. 3). A similar type 2-cyclohexyl-6-(tridecyl-1,3-dioxan-2-yl)azulene 1p gave a mesogen which showed a smectic A and a smectic B phase in of alignment is observed in mesogens with strongly polar groups.15 Our proposed structure for the SA phase is a bilayer the range 95–144 °C.All previously reported azulene mesogens J. Mater. Chem., 1997, 7(3), 391–401 393Table 2 Mesophase behaviour of azulene liquid crystals transition temperatures (microscopy) transition data (DSC) cis compound mp K1 mp/°C K2mp/°C (SA/I)/°C DH/kJ mol-1 Tonset/°C DS J K-1 mol-1 1c 81.4 100.1 — — 1d 83.6 99.6 — — 1e 94.5 94.5 76.8 83.9 4350 82 12.3 1f 96.9 97.8 — (84.1) 3350 79 9.5 1g 97.5 98.5 78.5 85.0 3440 79 9.8 1h 99.7 101.1 80.0 84.0 3150 79 9.0 1i 100.2 102.1 86.0 (83.9) 4210 80 11.9 1j 102.1 102.8 88.0 (79.5) 3290 77 9.4 1k 103.4 103.9 90.0 (78.9) 4000 75 11.5 are linked through ester groups.It is anticipated that substitution of the cyclohexyl ring by an alkyl chain will lead to a new homologous series with lower clearing points and transition temperatures.The linear dichroism of some azulene mesogens was determined by measuring the order parameter of these compounds as dyes in liquid crystal hosts. The optical order parameters were low as a result of the large angle which the transition moment makes with the molecular axis; in some cases this angle was close to the magic angle of 54°44¾ at which the dichroism is zero.As a result of the large angle, it was possible to vary the sign of the dichroism by varying the substituents on the azulene ring. However, these compounds are not suitable for use in guest–host displays despite the high extinction coefficients. Fig. 1 Phase diagram of compounds 1c –k: (a) K1–I; (1) SA–I; (p) Various aspects of the synthesis and physical properties of K2 – SA; (c) K2 –I azulene liquid crystals have been explored in this work.It is evident that the synthesis of azulene is difficult and having tried a number of routes, the most successful method for this work involved the reaction of N-alkylpyridinium salts with sodium cyclopentadienide. However, the development of new azulene based liquid crystals is restricted by the limited synthetic routes currently available.Experimental Fig. 2 Structures of the azuleneophanes Reactions sensitive to moisture and air were carried out in flame-dried glassware under nitrogen or argon using freshly distilled solvents. Solvents were dried and purified according to literature methods. Thin-layer chromatography on TLC aluminium sheets pre-coated with silica gel (Merck 69) F254 was used to monitor reactions and to establish the purity of samples.TLC plates were inspected using UV light or developed with iodine vapour. Oil-free sodium hydride was obtained by washing with dry light petroleum in an argon atmosphere. Amberlyst 15 (H+) ion-exchange resin was used in transacetalation reactions. Column chromatography separations were performed on silica gel (Merck 60) or neutral silica (Merck, 60) as the stationary phase.Loading of the sample was carried out either as a concentrated solution of the mixture in the solvent used for the mobile phase, or whenever the mixture was only sparingly soluble in the eluent, it was supported on silica gel by dissolving in a solvent, adding silica and evaporating the slurry to dryness to leave a powder which was poured on to the top of the column.Organic solutions were dried over magnesium sulfate unless otherwise stated. Melting points were determined using either a Reichert-Ko�fler hot-stage apparatus or a Zeiss-Labpol microscope equipped with crossed polarisers and a Linkam hot-stage with integrated temperature controller, and are uncorrected. Elemental analyses were performed by the University of Sheffield Microanalytical Service.Low resolution mass spectra were recorded using a Kratos MS 25 mass spectrometer. High resolution mass spectra was recorded using a Kratos MS 60 mass spectrometer to give Fig. 3 Proposed layer structure of the smectic A phase involving extensive interdigitation accurate mass values. 1H and 13C NMR spectra were recorded 394 J.Mater. Chem., 1997, 7(3), 391–401Table 3 Absorption frequencies and dichroic ratios for a range of azulene derivatives compound lmax/nm emax/cm2 mol-1 dichroic ratio AII/A) ref. 548 280000 1.0 17 565 340000 1.0 17 590 440000 1.44 17 480 720000 1.8a 3 510 630000 2.1a 3 468 560000 2.4 5 595 320000 0.72 — 550 354000 0.64 — 565 340000 0.50 — aExtrapolated from literature values.using SiMe4 as an internal standard in stated solvents. 10% K2CO3 solution (75 ml). This was extracted with diethyl ether (3×50 ml), dried and reduced to leave a colourless oil. Multiplicities are represented by the following abbreviations: s, singlet; d, doublet; t, triplet, q, quartet; m, multiplet; br, Purification by vacuum distillation gave unreacted pyridine-4- carbaldehyde, bp 73–74°C, 0.5 mmHg and 4-(diethoxymethyl)- broad signal.Coupling constants, (J) are given in Hz. pyridine as a colourless oil, bp 75–76 °C, 0.5 mmHg, 19 g, 81%; dH (250 MHz, CDCl3) 1.25(t, 6H, J 7, 2Me); 3.58[m, 4H, 4-(Diethoxymethyl ) pyridine 2(OCH2Me)]; 5.50[s, 1H, pyridine-CH-(OEt)2]; 7.40(d, 2H, J This compound was prepared by adapting the procedure of 6, pyridine); 8.70(d, 2H, J 6, pyridine); dC (63 MHz, CDCl3) Popp and McEwen,17 but full experimental details are given 15.0(q, 2C, 2Me); 61.2[t, 2C, 2(OCH2Me]; 99.8[d, 1C, pyri- below.A 13.5% solution of hydrogen bromide in ethanol was dine-CH-(OEt)2]; 121.6(d, 2C, pyridine); 147.6(s, 1C, pyridine); prepared by cooling ethanol (88 ml) to 0°C under nitrogen 149.9(d, 2C, pyridine); m/z (EI) 181(M+, 90%).and adding acetyl bromide (12 ml) dropwise. To a portion of this solution (52 ml) pyridine-4-carbaldehyde (11.2 g, N-Butyl-4-(diethoxymethyl )pyridinium bromide 105 mmol) was added to give a white precipitate and a yellow 4-(Diethoxymethyl)pyridine (4 g, 22.0 mmol) was dissolved in solution which was stirred at 20°C for 90 h. Dry benzene dry ethanol (10 ml) and 1-bromobutane (4.56 g, 33.0 mmol) (100 ml) was then added and any water formed during the added.The mixture was heated at reflux for 16 h. The ethanol reaction, removed by azeotropic distillation through a Soxhlet and excess 1-bromobutane were evaporated under reduced extractor containing MgSO4 , over a period of 24 h. Benzene pressure. The resulting yellow oil was left under high vacuum and ethanol were evaporated under reduced pressure to give an orange solid which was made alkaline (pH 9) by adding to remove any remaining solvent to give N-butyl-4-(diethoxy- J.Mater. Chem., 1997, 7(3), 391–401 395methyl)pyridinium bromide, (6.0 g, 85%), dH (250 MHz, 2-yl)pyridinium bromide remained contaminated with pro- CDCl3) 0.95[t, 3H, N(CH2)3CH3]; 1.25[t, 6H, 2(OCH2CH3)]; pane-1,3-diol, m/z (+ve FAB MS) C13H20NO2 222 (M+, 1.45[m, 2H, N(CH2)2CH2Me]; 2.05(m, 2H, NCH2CH2C2H5); 100%). 2.70(2H, br s, H2O); 3.65[q, 4H, 2(OCH2CH3)]; 5.05(t, 2H, NCH2C3H7); 5.70(s, 1H, (OEt)2-CH-pyridine); 8.15(d, 2H, pyri- 6-(1,3-Dioxan-2-yl )azulene, 1b dine); 9.60(d, 2H, pyridine); dC (63 MHz, CHCl3) 12.7(q, 1C, C3H7CH3);14.2[q, 2C, 2(OCH2CH3)]; 18.4(t, 1C, CH2); 32.9(t, Freshly distilled cyclopentadiene (2.19 ml, 33.2 mmol) was 1C, CH2); 33.0(t, 1C, CH2 ); 60.2(t, 1C, CH2); 61.5[t, 2C, added dropwise to sodium hydride (0.40 g, 16.7 mmol) in THF 2(OCH2CH3)]; 91.3(d, 1C, (OEt)2-CH-pyridine); 97.4(d, 2C, (30 ml) at 0°C over 30 min and then allowed to warm to 2-pyridine); 125.3(d, 2C, 3-pyridine); 156.7(s, 1C, 4-pyridine); 20°C.Crude N-butyl-4-(1,3-dioxan-2-yl)pyridinium bromide m/z (+ve FAB MS) C14H24NO2 238 (M+, 100%).(1.9 g, 6.28 mmol), dissolved in THF (10 ml), was then added to the pink solution giving a colour change to dark orange and then brown. The mixture was heated at reflux for 3 h. 6-(Diethoxymethyl ) azulene, 1a Water (50 ml) was then added and the mixture extracted with dichloromethane (4×50 ml): the combined organic layers Freshly distilled cyclopentadiene (2.42 g, 36.6 mmol) was added were dried and solvent evaporated under reduced pressure.dropwise over 30 min to sodium hydride (0.88 g, 36.6 mmol) Purification by column chromatography on silica using in THF (70 ml) at 0°C and then allowed to warm to 20°C. dichloromethane as eluent gave 6-(1,3-dioxan-2-yl)azulene as N-butyl-4-(diethoxymethyl)pyridinium bromide (17.5 g, dark blue microprisms.Recrystallisation from pentane gave 55.0 mmol) dissolved in THF (50 ml) was then added to the the pure product, (0.195 g, 15%), mp 110–111°C (Found: C, pinkish solution which went dark red and then brown. The 78.3; H, 6.6; C14H14O2 calculated: C, 78.5; H, 6.6%); dH mixture was heated at reflux for 3 h, a blue spot being indicated (250 MHz, CDCl3) 1.45(m, 1H, dioxanyl); 2.25(m, 1H, diox- by TLC.THF was evaporated under reduced pressure to leave anyl); 4.00(m, 2H, dioxanyl); 4.30(m, 2H, dioxanyl); 5.50(s, a black viscous oil to which silica was added. Purification by 1H, H-C-azulene); 7.40(d, 2H, J 10, azulene H-C1,3); 7.40(d, column chromatography using light petroleum (bp 40–60°C) 2H, J 4, azulene H-C5,7 ); 7.90(t, 1H, J 4, azulene H-C2); 8.40(d, as eluent gave 6-(diethoxymethyl)azulene as a dark blue oil 2H, J 10, azulene H-C4); dC (60 MHz, CDCl3) 25.7(t, 1C, (2.72 g, 32%).Further purification using a Ku� gelrohr appar- CH2); 67.6 [t, 2C, (OCH2)2]; 104.3(d, 1C, H-C-azulene); atus gave 1a (Found: C, 78.0; H, 7.9. C15H18O2 calculated: C, 118.1(d, 2C, azulene C1,3); 121.1(d, 2C, azulene C5,7); 135.2(d, 78.2, H, 7.9%), dH (250 MHz, CDCl3) 1.25(t, 6H, 2Me); 3.6[m, 2C, azulene C4,8); 135.9(d, 1C, azulene C2 ); 140.1(s, 2C, azulene 4H, 2(OCH2CH3)]; 5.45[s, 1H, HC(OEt)2]; 7.40(m, 4H, azu- C3a,8a); 146.0(s, 1C, azulene C6); m/z (EI) 214 (M+, 83%).lene H-C1,3,5,7); 7.90(t, 1H, J 4, azulene H-C2); 8.35 (d, 2H, azulene H-C4,8 ); dC (60 MHz, CDCL3) 15.2 (q, 1C, Me); 61.8[t, 2C, (OCH2Me)2]; 104.4[d, 1C, H-C(OEt)2 ]; 118.1(d, 2C, azu- cis- and trans-6-(5-Pentyl-1,3-dioxan-2-yl )azulene, 1c lene C1,3 ); 121.4(d, 2C, azulene C5,7); 135.8(d, 2C, azulene C4,8); 137.3(s, 1C, azulene C2); 139.9(s, 2C, azulene C3a,8a); Compound 1a (0.35 g, 1.52 mmol) and 2-pentylpropane-1,3- 147.3(s, 1C, azulene C6); m/z (EI) 230 (M+, 80%).diol (0.33 g, 2.28 mmol) were stirred together in dry benzene (10 ml) with an ion exchange resin (catalytic amount) at 100°C for 6 h and the reaction was followed by TLC.Purification of the products was attempted by column chromatography on 4-(1,3-Dioxan-2-yl )pyridine silica using hexane–dichloromethane (351) as eluent which A 13.5% solution of HBr in propane-1,3-diol was prepared by gave the mixture of isomers as blue microprisms (170 mg, cooling propane-1,3-diol (88 ml) to 0°C under nitrogen and 39%).These were shown, by analytical HPLC, to be a mixture adding acetyl bromide (12 ml) dropwise. To a portion of this of the cis- and trans-forms in a ratio of 253. Separation was solution (52 ml) was added pyridine-4-carbaldehyde (11.2 g, achieved using reverse phase HPLC to give the pure isomers, 105 mmol) and the solution was stirred at 20 °C for 90 h.Dry cis-6-(5-pentyl-1,3-dioxan-2-yl)azulemp 81.4°C; (M+ benzene (100 ml) was then added and any water formed during Found: 284.1785, C19H24O2 requires: 284.17762); dH (250 MHz, the reaction, removed by azeotropic distillation through a CD2Cl2) 0.9(t, 3H, J 7, Me); 1.35[m, 7H, CH2(CH2)3Me, C- Soxhlet extractor containing MgSO4, over a period of 24 h.HC5H9]; 1.83(m, 2H, CH2C4H9 ); 4.10(m, 4H, (OCH2)2];5.52(s, Benzene and ethanol were then evaporated under reduced 1H, H-C-azulene); 7.38(d, 2H, J 4, azulene H-C1,3); 7.38(d, 2H, pressure to give an orange solid which was made alkaline J 10, azulene H-C5,7); 7.90(t, 1H, J 4, azulene H-C2); 8.37(d, (pH 9) by adding 10% K2CO3 solution (75 ml). This was 2H, J 10, azulene H-C4,8 ); dC (63 MHz, CD2Cl2 ) 14.1(q, 1C, extracted with diethyl ether (3×50 ml), dried and reduced Me); 22.7(t, 1C, CH2); 27.3(t, 1C, CH2 ) 29.6(t, 1C, CH); 32.0(t, to leave a brown oil.Purification by vacuum distillation 1C, CH2 ); 34.4[d, 1C, HC(CH2O)2]; 71.0(t, 2C, (CH2O)2 ]; gave unreacted pyridine-4-carbaldehyde and a small amount 104.7(d, 1C, H-C-azulene); 118.2(d, 2C, azulene C1,3); 121.2(d, of product, bp 68–71 °C at 0.6 mmHg (3.62 g, 21%) as a 2C, azulene C5,7); 136.1(d, 2C, azulene C4,8); 137.6(d, 1C, mixture of 4-(1,3-dioxan-2-yl)pyridine (1.05 g, 6.1% from azulene C2); 140.1(s, 2C, azulene C3a,8a); 146.0(s, 1C, azulene 1H NMR) and propane-1,3-diol as a colourless oil at C6); m/z (EI) 284 (M+, 92%); and trans-6-(5-pentyl-1,3-dioxan- 71–100°C at 0.6 mmHg, dH (220 MHz, CDCl3); 1.70(m, 2H, 2-yl) azulene, mp 100.1°C; (M+ Found: 284.1783, C19H24O2 OCH2CH2CH2O); 4.0(m, 4H, OCH2CH2CH2O); 5.50(s, 1H requires: 284.17762); dH (250 MHz, CD2Cl2) 0.90(t, 3H, J 7, 1,3-dioxan-2-yl-CH-pyridine); 7.70(d, 2H, 2-pyridine); 8.70(d, Me); 1.10(m, 2H, C3H7CH2Me); 1.30[m, 6H, (CH2 )3C2H5 ]; 2H, 3-pyridine); and signals for propane-1,3-diol; m/z (+CI) 2.20(m, 1H, C-HC5H9); 3.58(t, 2H, J 12, OCH2); 4.28(q, 2H, C9H11NO2 165 (M+, 100%).J 4.5, OCH2); 5.45(s, 1H, H-C-azulene); 7.38(d, 2H, J 4, azulene H-C1,3); 7.38(d, 2H, J 10, azulene H-C5,7); 7.90(t, 1H, J 4, azulene H-C2); 8.35(d, 2H, J 10, azulene H-C4,8 ); dC (63 MHz, N-Butyl-4-(1,3-dioxan-2-yl ) pyridinium bromide CD2Cl2) 14.1(q, 1C, Me); 22.5(t, 1C, CH2); 26.0(t, 1C, CH2 ); 28.2(t, 1C, CH); 32.0(t, 1C, CH2); 34.2[d, 1C, HC(CH2O)2 ]; The crude mixture of 4-(1,3-dioxan-2-yl)pyridine (1.05 g, 72.9[t, 2C, (CH2O)2]; 104.3(d, 1C, H-C-azulene); 118.2(d, 2C, 6.36 mmol) and 1-bromobutane (4.5 g, 33.0 mmol) was added azulene C1,3 ); 121.2 (d, 2C, azulene C5,7); 136.0(d, 2C, azulene to dry ethanol (10 ml) and heated at reflux for 16 h, the C4,8 ); 137.6(d, 1C, azulene C2); 140.1(s, 2C, azulene C3a,8a); reaction being followed by TLC. The ethanol was evaporated under reduced pressure but the product N-butyl-4-(1,3-dioxan- 145.9(s, 1C, azulene C6); m/z (EI) 284 (M+, 100%). 396 J. Mater. Chem., 1997, 7(3), 391–401The series of homologues were all prepared in a similar H-C1,3,5,7 and phenyl); 7.95(t, 1H azulene H-C2); 8.45(d, 2H, azulene H-C4,8); dC (63 MHz, CDCl3) 41.1(d, 1C, H-C-Ph); manner and the reaction conditions are outlined in Table A.Table A 72.6[t, 2C, (OCH2)2]; 104.2(d, 1C, H-C-azulene); 118.3(d, 2C, azulene C1,3); 121.2(d, 2C, azulene C5,7); 127.6(d, 1C, Ph); temperature/°C, cis5trans 127.7(d, 2C, Ph); 128.9(d, 2C, Ph); 136.0(d, 2C, azulene C4,8 ); compound catalyst solvent time/h yield (%) ratio 137.4(s, 1C, Ph) 137.7(d, 1C, azulene C2 ); 140.2(s, 2C, azulene C3a,8a); 145.6(s, 1C, azulene C6); m/z (EI) 290 (M+, 85%). 1d TsOH — 55/48 22 253 1e i-e resin Benzene 80/20 16 255 This procedure was used to prepare 1m and 1n (Table C) 1f i-e resin CH2Cl2 50/20 13 153 by reaction with the appropriate diol. 1g i-e resin Benzene reflux/4 23 153 1h i-e resin Benzene reflux/8 6 153 cis- and trans-6-[5-(4-Hexyloxyphenyl )-1,3-dioxan-2-yl]- 1i i-e resin Benzene 100/8 26 153 1j i-e resin Toluene reflux/4 41 153 azulene, 1m 1k i-e resin Toluene 100/8 39 153 cis-6-[5-Hexyloxyphenyl)-1,3-dioxan-2-yl]azulene, mp 143 °C (decomp.) and the trans-6-[5-(4-hexyloxyphenyl)-1,3-dioxan- All the above compounds gave 1H NMR, 13C NMR and mass 2-yl]azulene, mp 225°C, dH (250 MHz, CD2Cl2) 0.89(t, 3H, spectra analogous to those for the 6-(5-pentyl-1,3-dioxan-2- J 7, Me); 1.40[m, 6H, C2H4(CH2)3Me]; 1.75(m, 2H, yl)azulene isomers described above.CH2CH2C4H9 ); 3.33(m, 1H, H-C-phenyl); 3.92(t, 2H, J 7, The high resolution mass spectra values for each compound dioxanyl CH2); 4.02(t, 2H, J 11.5, OCH2C5H11); 4.32(q, 2H, J are given in Table B. 11.5, dioxanyl CH2); 5.6(s, 1H, H-C-azulene); 6.86(d, 2H, J 8.5, Table B phenyl); 7.16(d, 2H, J 8.5, phenyl); 7.38(d, 2H, J 4.5, azulene H-C1,3); 7.42(d, 2H, J 10.5, azulene H-C5,7); 7.9(t, 1H, J 4.5, molecular found found azulene H-C2); 8.39(d, 2H, J 10.5, azulene H-C4,8 ); dC (63 MHz, compound formula calc. cis trans CD2Cl2) 14.2(q, 1C, Me); 23.0(t, 1C, CH2); 26.1(t, 1C, CH2 ); 1d C20H26O2 298.1933 298.1941 298.1926 29.6(t, 1C, CH2); 32.0(t, 1C, CH2); 40.7[t, 1C, H-C-(OCH2)]; 1e C24H34O2 354.2559 354.2542 354.2547 68.5(t, 1C, OCH2 ); 73.1[d, 2C, dioxanyl 2(OCH2)]; 104.3(d, 1f C25H36O2 368.2715 368.2719 368.2711 1C, H-C-azulene); 115.1(d, 2C, phenyl); 118.5(d, 2C, azulene 1g C26H38O2 382.2872 382.2882 382.2862 C1,3 ); 121.6(d, 2C, azulene C5,7); 129.0(d, 2C, phenyl); 129.6(s, 1h C27H40O2 396.3028 396.3046 396.3012 1C, phenyl); 136.2(d, 2C, azulene C4,8 ); 138.0(d, 1C, azulene 1i C28H42O2 410.3185 410.3178 410.3166 1j C29H44O2 424.3341 424.3348 424.3346 C2); 140.4(s, 2C, azulene C3a,8a); 146.4(s, 1C, phenyl); 158.9(s, 1k C30H46O2 438.3498 438.3489 438.3490 1C, azulene C6); m/z (EI) 390 (M+, 62%).cis- and trans-6-(5-Phenyl-1,3-dioxan-2-yl ) azulene, 1l cis- and trans-6-[5-(4-dodecyloxyphenyl )-1,3-dioxan-2-yl]- azulene, 1n Compound 1a and 2-phenylpropane-1,3-diol (0.5 g, 3.26 mmol) were stirred together with the ion-exchange catalyst at 60°C cis-6-[5-(4-Dodecyloxyphenyl)-1,3-dioxan-2-yl]azulene, mp 127°C (M+ Found: 474.3139, C32H42O3 calculated: 474.3134); in dry THF (5 ml) for 2 h.The reaction was monitored by TLC; when all the starting material had disappeared the dH (250 MHz, CD2Cl2) 0.86(t, 3H, J 7, Me); 1.26[m, 18H, CH2(CH2 )9Me]; 1.75(m, 2H, CH2CH2C9H18Me); 2.75(m, 1H, reaction mixture was filtered to remove the resin and the product washed through with ethyl acetate.Purification by CH-phenyl-OC12H25); 3.94(t, 2H, OCH2C11H23); 4.38[m, 4H, 2(dioxanyl CH2)]; 5.68(s, 1H, dioxanylMCHMazulene); 6.89(d, column chromatography on silica, using light petroleum (bp 40–60°C)–ethyl acetate, 451, as eluent gave a mixture of 2H, J 9, phenyl); 7.39(m, 4H, azulene H-C1,3,5,7); 7.53(d, 2H, J 9, phenyl); 7.90(t, 1H, J 4, azulene H-C2); 8.39(d, 2H, J 11, the cis- and trans-isomers as dark blue microprisms, 0.532 g, 53%.These were shown, by analytical HPLC to be a mixture azulene H-C4,8 ); dC (63 MHz, CD2Cl2) 14.25(q, 1C, Me); 23.1(t, 1C, CH2); 26.4(t, 1C, CH2); 29.7[t, 2C, 2(CH2 )]; 29.8[t, 4C, of the cis- and trans-forms in a ratio 152.Separation of the isomers was achieved by reverse phase chromatography; recrys- 4(CH2)]; 30.0(t, 1C, CH2); 32.3(t, 1C, CH2); 38.6(t, 1C, dioxanyl- CH phenyl-OC12H25); 68.4(t, 1C, OCH2C11H23); 72.2[d, tallisation from diethyl ether–light petroleum gave the pure isomers; cis-6-(5-phenyl-1,3-dioxan-2-yl)azulene, mp 123 °C 2C, dioxanyl 2(OCH2)]; 104.8(d, 1C, dioxanyl-HC-azulene); 114.6(d, 2C, phenyl); 118.5(d, 2C, azulene C1,3); 121.6(d, 2C, (M+ Found: 290.1302, C20H18O2 calculated: 290.1307); dH (250 MHz, CDCl3 ) 2.75(m, 1H, dioxanyl); 4.4(m, 4H, diox- azulene C5,7); 129.7(d, 2C, phenyl); 135.2(s, 1C, phenyl); 136.3(d, 2C, azulene C4,8); 138.0(d, 1C, azulene C2); 140.4(s, anyl); 5.79(s, 1H, H-C-azulene); 7.7(m, 2H, phenyl); 7.47(d, 2H, J 11, azulene H-C5,7); 7.35(m, 5H, phenyl and azulene H- 2C, azulene C3a,8a); 146.5(s, 1C, phenyl); 158.3(s, 1C, azulene C6); m/z (EI) 474 (M+, 100%); and trans-6-[5-(4-dodecyloxy- C1,3); 7.9(t, 1H, J 4, azulene H-C2); 8.45(d, 2H, J 11, azulene H-C4,8); dC (63 MHz, 2H6 acetone) 39.5(d, 1C, H-C-Ph); 72.1[t, phenyl)-1,3-dioxan-2-yl]azulene, mp 206 °C (crystal SB) (M+ Found: 474.3123, C32H42O3 calculated: 474.3134); dH 2C, (OCH2 )2 ]; 104.9(d, 1C, H-C-azulene); 118.8(d, 2C, azulene C1,3); 122.2(d, 2C, azulene C5,7); 126.9(d, 1C, Ph); 128.9(d, 2C, (250 MHz, CD2Cl2) 0.88(t, 3H, J 7, Me); 1.30[m, 18H, CH2(CH2 )9Me]; 1.75(m, 2H, CH2CH2C9H18Me); 3.34(m, 1H, Ph); 129.2(d, 2C, Ph); 136.5(d, 2C, azulene C4,8); 138.1(s, 1C, Ph); 140.8(d, 1C, azulene C2); 144.3(s, 2C, azulene C3a,8a); CH-phenyl-OC12H25); 3.94(t, 2H, J 7, OCH2C11H23); 4.04(t, 2H, J 11.5, dioxanyl CH2 ); 4.34(q, H, J 4.5, dioxanyl CH2 ); 147.4(s, 1C, azulene C6); m/z (EI) 290 (M+, 45%); and trans- 6-(5-phenyl-1,3-dioxan-2-yl)azulene, mp 193 °C (M+ Found: 5.68(s, 1H, dioxanyl-CH-azulene); 6.88(d, 2H, J 9, phenyl); 7.17(d, 2H, J 9, phenyl); 7.42(m, 4H, azulene H-C1,3,5,7); 7.92(t, 290.1302, C20H18O2 calculated: 290.1307); dH (250 MHz, CDCl3) 3.45(m, 1H, dioxanyl); 4.10(t, 2H, dioxanyl); 4.45(q, 1H, J 4, azulene H-C2); 8.40(d, 2H, J 11, azulene H-C4,8); dC (63 MHz, CD2Cl2) 14.24(q, 1C, Me); 23.1(t, 1C, CH2); 26.4(t, 2H, dioxanyl); 5.65(s, 1H, H-C-azulene); 7.30(m, 9H, azulene Table C compound alkyl chain catalyst solvent temperature/°C, time/h yield (%) cis5trans 1m OC6H13 i-e resin THF 60/48 7 154 1n OC12H25 i-e resin THF 100/8 14 153 J.Mater. Chem., 1997, 7(3), 391–401 3971C, CH2); 26.4(t, 1C, CH2); 29.6[t, 2C, 2(CH2)]; 29.7[t, 4C, CDCl3) 14.1(q, 1C, Me); 21.3(q, 1C, Me); 21.4(q, 1C, Me); 22.7(q, 1C, Me); 22.8(t, 1C, CH2); 26.4(t, 1C, CH2); 26.9(t, 1C, 4(CH2)]; 30.0(t, 1C, CH2); 32.3(t, 1C, CH2); 40.7(t, 1C, diox- CH2); 28.2(t, 1C, CH2); 29.4(t, 1C, CH2); 29.5(t, 1C, CH2 ); anyl-HC phenyl-OC12H25); 68.4(t, 1C, OCH2C11H23); 73.1(d, 29.7(t, 4C, CH2); 29.8(t, 1C, CH2); 30.5(d, 1C, CH); 31.9(t, 1C, 2C, dioxanyl 2(OCH2)); 104.3(d, 1C, dioxanyl-HC-azulene); CH2); 34.2(d, 1C, CH); 35.7(t, 1C, CH2); 39.6(d, 1C, CH); 115.1(d, 2C, phenyl); 118.5(d, 2C, azulene C1,3); 121.6(d, 2C, 42.9[t, 1C, H-C(CH2O)2 ]; 48.2(d, 1C, neomenthyl H-C-azu- azulene C5,7); 129.0(d, 2C, phenyl); 129.6(s, 1C, phenyl); lene); 72.9[t, 2C, 2(OCH2Me)]; 104.6(d, 1C, dioxanyl H-C- 136.2(d, 2C, azulene C4,8 ); 138.0(d, 1C, azulene C2); 140.4(s, azulene); 119.6(d, 2C, azulene C1,3); 121.2(d, 2C, azulene C5,7); 2C, azulene C3a,8a); 146.4(s, 1C, phenyl); 158.9(s, 1C, azulene 133.7(d, 2C, azulene, C4,8 ); 139.7(s, 2C, azulene C3a,8a); 144.0(s, C6); m/z (EI) 474 (M+, 100%). 1C, azulene C6); 158.5(s, 1C, azulene C2); m/z (EI) 506 (M+, 18%). 2-(+)-Neomenthyl-6-(diethoxymethyl) azulene (+)-Neomenthylcyclopentadiene18 (2 g, 9.8 mmol, 1.1 equiv.) 1-Cyclohexyl-6-(diethoxymethyl) azulene and 2-cyclohexyl-6- was added to sodium hydride (0.21 g, 8.90 mmol, 1 equiv.) in (diethoxymethyl )azulene dry THF (30 ml) at 20°C to give a slightly pink solution.After Cyclohexylcyclopentadiene, (1 g, 6.76 mmol) was added to 30 min, when no further reaction was observed, N-butyl-4- sodium hydride (0.2 , 8.33 mmol) in THF (30 ml) and heated (diethoxymenthyl)pyridinium bromide (5.0 g, 15.0 mmol, 2 gently until the reaction had completed, to give a red solution.equiv.) in THF (20 ml) was added to give a dark brown Butyl-4-(diethoxymethyl)pyridine bromide (5.0 g, 15.0 mmol) solution which was heated at reflux for 16 h. Solvent was was added in THF (25 ml) and heated at reflux for 90 h. evaporated under reduced pressure and alumina added. Solvent was evaporated under reduced pressure and neutral Purification by column chromatography was attempted on silica added to the dark brown oil.Purification by column basic alumina using hexane as eluent to give an unidentified chromatography on neutral silica using light petroleum as yellow oil and 2-(+)-neomenthyl-6-(diethoxymenthyl)azulene eluent gave a colourless oil identified as N-butyl-(4-ethoxycar- as a dark blue oil 0.74 g, 22.6% (Found: 368.2706, C25H36O2 bonyl-4-ethyl)dihydropyridine, 0.5 ml, 14%, dH (250 MHz, calculated: 368.2715); dH (250 MHz, CDCl3 ) 0.8(t, 6H, 2Me); CDCl3) 0.81(t, 3H, J 7.5, CH2CH3); 0.89(t, 3H, J 7.5, 1.30(m, 18H, neomenthyl); 2.20(m, 1H, neomenthyl H-C-azu- NC3H6CH3); 1.24(t, 3H, J 7.5, COOCH2CH3); 1.27(m, lene); 3.60(t, 2H, OCH2); 3.55[m, 4H, 2(OCH2Me)]; 7.30(s, 2H, NC2H4CH2Me); 1.44(m, 2H, NCH2CH2C2H5); 1.49(q, 2H, azulene H-C1,3); 7.35(d, 2H, azulene H-C5,7); 8.25(d, 2H, 2H, J 7.5, CH2Me); 3.20(t, 2H, J 7, NCH2C3H7); 4.13(q, azulene H-C4,8); dC (63 MHz, CDCl3 ) 15.2(q, 2C, Me); 21.3(q, 2H, J 7, COOCH2Me); 4.40(d, 2H, J 8, b-dihydropyridine); 1C, Me); 21.4(q, 1C, Me): 22.8(q, 1C, Me); 26.5(t, 1C, CH2); 5.93(d, 2H, J 8, a-dihydropyridine); dC (63 MHz, CDCl3) 26.9(d, 1C, CH); 30.5(d, 1C, CH); 35.7(t, 1C, CH2); 39.6(d, 1C, 8.5(q, 1C, CH2CH3); 13.8(q, 1C, NC3H6CH3); 14.1(q, CH); 43.0(t, 1C, CH2 ); 48.2[d, 1C, (+)-neomenthyl H-C- 1C, COOCH2CH3); 19.7(t, 1C, NC2H4CH2Me); 32.3(d, 1C, azulene]; 61.9[t, 2C, 2(OCH2)Me]; 104.5(d, 1C, diethoxy H- NCH2CH2C2H5); 35.1(t, 1C, CH2Me); 46.6(s, 1C, c-dihydro- C-azulene); 119.6(d, 2C, azulene C1,3 ); 121.5(d, 2C, azulene pyridine); 53.1(t, 1C, NCH2C3H7); 60.4(t, 1C, OCH2Me); C5,7); 133.6(d, 2C, azulene C4,8); 139.5(s, 2C, azulene C3a,8a); 98.4(d, 2C, b-dihydropyridine); 130.2(d, 2C, a-dihydropyridine); 145.3(s, 1C, azulene C6); 158.3(s, 1C, azulene C2); m/z (EI) 368 176.5(s, 1C, COOEt), and a mixture of the isomers as a dark- (M+, 50%).blue oil, 0.533 g, 25%.Separation of the isomers was achieved by MPLC to give 1-cyclohexyl-6-(diethoxymethyl)azulene, as cis- and trans-2-Neomenthyl-6-(5-undecyl-1,3-dioxan-2-yl )- a purple–blue oil, (Found: 312.2103, C21H28O2 calculated: azulene, 1o 312.2089); dH (250 MHz, CD2Cl2) 1.30[t, 6H, 2(OCH2Me)]; 1.70(m, 10H, cyclohexyl); 3.25(m, 1H, azulene CH-cyclohexyl); 2-Neomenthyl-6-(diethoxymethyl)azulene (0.6 g, 1.63 mmol) 3.55[m, 4H, 2(OCH2Me)]; 5.35[s, 1H, (EtO)2CH-azulene]; and 2-undecylpropane-1,3-diol (0.6 g, 2.61 mmol) were heated 7.15(d, 2H, azulene H-C5,7 ); 7.2(d, 1H, azulene H-C3); 7.75(d, to 60°C together with an ion-exchange resin (catalytic amount) 1H, azulene H-C2); 8.15(d, 1H, azulene H-C4); 8.25(d, 1H, in dry ethyl acetate (3 ml) for 1 h.The reaction was monitored azulene H-C4); dC (63 MHz, CD2Cl2) 15.4[q, 2C, 2(OCHMe)]; by TLC and solvent evaporated under reduced pressure when 26.8(t, 1C, cyclohexyl); 27.6(t, 2C, cyclohexyl); 35.6(t, 2C, starting material had disappeared. Purification was achieved cyclohexyl); 37.0(d, 1C, azulene CH-cyclohexyl); 62.4[t, 2C, by column chromatography on neutral silica using light pet- 2(OCH2Me)]; 105.1[d, 1C, (EtO)2CH-azulene]; 117.3(d, 1C, roleum–diethyl ether, 451, as eluent to give the mixture of azulene C3); 120.1(d, 1C, azulene C5); 120.8(d, 1C, azulene C7); isomers as blue microprisms, 150 mg, 18%.Separation of the 132.6(d, 1C, azulene C2); 134.6(s, 1C, azulene C1); 135.1(d, 1C, isomers (cis/trans: 1/3) was achieved by HPLC to give cis-2- azulene C4); 135.8(d, 1C, azulene C8); 137.9(s, 1C, azulene neomenthyl-6-(5-undecyl-1,3-dioxan-2-yl)azulene, as a blue oil, C3a); 140.6(s, 1C, azulene C8a); 148.0(s, 1C, azulene C6 ); m/z dH (250 MHz, CDCl3) 1.30(m, 43H, neomenthyl and C11H23); (EI) 312 (M+, 100%), and 2-cyclohexyl-6-(diethoxymethyl)- 4.05[s, 4H, 2(OCH2)]; 5.45(s, 1H, dioxanyl H-C-azulene); azulene, as blue microprisms, mp 58–59 °C (Found 312.2074, 7.20(s, 2H, azulene H-C1,3); 7.25(d, 2H, azulene H-C5,7); 8.25(d, C21H28O2 calculated: 312.2089); dH (250 MHz, CD2Cl2) 0.90[t, 2H, azulene H-C4,8); dC (63 MHz, CDCl3 ) 14.1(q, 1C, Me); 6H, 2(OCH2Me)]; 1.80(m, 10H, cyclohexyl); 2.90(m, 1H, azu- 21.2(q, 1C, Me); 21.4(q, 1C, Me); 22.7(q, 1C, Me); 22.8(t, 1C, lene CH-cyclohexyl); 3.65[m, 4H, 2(OCH2Me)]; 4.45 [s, 1H, CH2); 26.4 (t, 1C, CH2); 26.9 (t, 1C, CH2); 27.6 (t, 1C, CH2); (EtO)2CH-azulene]; 7.20(s, 2H, azulene H-C1,3); 7.30(d, 2H, 28.2 (t, 1C, CH2); 29.4(t, 1C, CH2); 29.7[t, 5C, 5(CH2)]; 30.5(d, azulene H-C5,7); 8.20(d, 2H, azulene H-C4,8); dC (63 MHz, 1C, CH); 31.9(t, 1C, CH2); 34.4(d, 2C, CH); 35.7(t, 1C, CH2); CD2Cl2) 5.2[q, 2C, 2(OCH2Me)]; 16.6(t, 1C, cyclohexyl); 39.6(d, 1C, CH); 42.9[t, 1C, H-C(CH2O)2]; 48.2(d, 1C, neo- 16.9(t, 2C, cyclohexyl); 24.5(t, 2C, cyclohexyl); 30.3(d, 1C, menthyl H-C-azulene); 70.9[t, 2C, 2(OCH2Me)]; 104.9(d, 1C, azulene CH-cyclohexyl); 94.9[t, 2C, 2(OCH2Me)]; 106.0[d, dioxanyl H-C-azulene); 119.6(d, 2C, azulene C1,3 ); 121.2(d, 2C, 1C, (EtO)2CH-azulene]; 111.7(d, 2C, azulene C1,3); 123.9(d, azulene C5,7); 133.8(d, 2C, azulene C4,8); 139.7(s, 2C, azulene 2C, azulene, C5,7); 130.3(d, 2C, azulene C4,8); 130.3(s, 2C, C3a,8a); 144.2(s, 1C, azulene C6); 158.5(s, 1C, azulene C2); and azulene C3a,8a); 135.9(s, 1C, azulene C6); 151.4(s, 1C, azulene trans-2-neomenthyl-6-(5-undecyl-1,3-dioxan-2-yl)azulene, as C2); m/z (EI) 312 (M+, 100%).blue microprisms, mp 53–43 °C, dH (250 MHz, CDCl3) 1.30(m, cis- and trans-2-Cyclohexyl-6-(5-tridecyl-1,3-dioxan-2-yl )- 42H, neomenthyl and C11H23); 2.20(m, 1H, neomenthyl H-Cazulene, 1p azulene); 3.60(t, 2H, OCH2); 4.30(q, 2H, OCH2); 5.45(s, 1H, dioxanyl H-C-azulene); 7.30(s, 2H, azulene H-C1,3); 7.35(d, 2H, 2-Cyclohexyl-6-(diethoxymethyl)azulene (0.28 g, 0.90 mmol) and tridecylpropane-1,3-diol (0.3 g, 1.15 mmol) were dissolved azulene H-C5,7 ); 8.25(d, 2H, azulene H-C4,8); dC (63 MHz, 398 J.Mater. Chem., 1997, 7(3), 391–401in dry benzene (20 ml) and heated at 80°C with an ion to give colourless crystals of 4-(ethylenedioxy)cyclohexyl tosylate, 7.2 g, 73%, dH (250 MHz, CDCl3) 1.75(m, 8H, cyclohexyl exchange resin (catalytic amount) for 3 h. Solvent was evaporated under reduced pressure to leave a black product.CH2s); 2.45(s, 3H, Me); 3.90(m, 4H, ketal CH2s); 4.60(m, 1H, HCOTs); 7.30(d, 2H, phenyl); 7.80(d, 2H, phenyl): m/z (EI) Purification was attempted by column chromatography on neutral silica using light petroleum with 1% diethyl ether as 211 (M+, 25%). eluent to give the pure trans-2-cyclohexyl-6-(5-tridecyl-1,3- 4-(Ethylenedioxy)cyclohexylcyclopentadiene dioxan-2-yl)azulene, as blue microprisms (Found: C, 82.73; H, 10.80; C33H50O2 calculated: C, 82.79; H, 10.52%); dH (250 MHz, This was prepared by following the literature procedure for CD2Cl2) 0.80(t, 3H, J 7, Me); 1.1(m, 2H, cyclohexyl CH2); the synthesis of (+)-neomenthylcyclopentadiene by Cesarotti 1.20(m, 22H, C11H22C2H5 ); 1.45(m, 6H, cyclohexyl); 1.70(m, and Kagan,19 but full experimental details are given below. 4H, cyclohexyl); 2.05(m, 1H, HC-C13H27); 2.85(m, 1H, azulene Freshly distilled cyclopentadiene (12 ml, 0.177 M) was added CH-cyclohexyl); 3.46(t, 2H, J 11 Hz, OCH2 ); 4.16(q, 2H, J 5, dropwise to sodium hydride (3.4 g, 0.142 M) in THF (25 ml) at OCH2); 5.70(s, 1H, dioxanyl HC-azulene); 7.14(s, 2H, azulene 0°C to give a pink solution. When the reaction had completed H-C1,3); 7.21(d, 2H, J 10.5, azulene H-C5,7 ); 8.13(d, 2H, J this was syringed into a solution of 4-(ethylenedioxy)cyclohexyl 10.5 Hz), azulene H-C4,8); dC (63 MHz, CD2Cl2) 14.3(q, 1C, tosylate (11 g, 35.5 mmol) in THF (50 ml) and heated at reflux Me), 23.1(t, 1C, CH2); 26.7(t, 1C, cyclohexyl); 27.1(t, 2C, for 16 h to leave dark red colour.Water was then added, the cyclohexyl); 28.5(t, 1C, CH2); 29.7(t, 1C, CH2 ); 29.9[t, 8C, now dark brown solution filtered through a Bu� chner funnel 8(CH2)]; 30.1(t, 1C, CH2); 32.3(t, 2C, cyclohexyl); 34.6(d, 1C, and solvent evaporated from the filtrate under reduced pressure HC-C13H27); 40.5(d, 1C, azulene CH-cyclohexyl); 73.2[t, 2C, to leave a brown oil.Purification by vacuum distillation 2(OCH2)]; 104.7(d, 1C, dioxanyl HC-azulene); 116.2(d, 2C, (0.5 mmHg, 140 °C) gave 4-(ethylenedioxy)cyclohexylcyclopen- azulene C1,3); 121.7(d, 2C, azulene C5,7); 134.1(d, 2C, azulene tadiene as a yellow oil, 2.5 g, 34%, dH (250 MHz, CDCl3) C4,8); 140.6(s, 2C, azulene C3a,8a); 144.7(s, 1C, azulene C6); 1.75(m, 8H, cyclohexyl CH2s); 2.30[m, 1H, cyclopentadienyl- 161.9(s, 1C, azulene C2); m/z (EI) 478 (M+, 100%).MPLC on CH(cyclohexyl)]; 2.95(m, 2H, cyclopentadiene; 3.95(m, 4H, silica gave the pure cis-2-cyclohexyl-6-(5-tridecyl-1,3-dioxan-2- ketal CH2s); 6.00–6.50(m, 3H, cyclopentadiene).yl)azulene, as purple microprisms, mp 86–87 °C (M+, calculated: 479.3882, C33H50O2 found: 479.3889); dH (250 MHz, 1-[4-(Ethylenedioxy) cyclohexyl]-6-(diethoxymethyl )azulene CD2Cl2) 0.86(t, 3H, J 7, Me); 1.1(m, 2H, cyclohexyl CH2); and 2-[4-(ethylenedioxy)cyclohexyl]-6-(diethoxymethyl )azulene 1.30(m, 22H, C11H22C2H5 ); 1.50(m, 6H, cyclohexyl); 1.80(m, 4H, cyclohexyl); 2.08(m, 1H, HC-C13H27); 2.92(m, 1H, azulene 4-(Ethylenedioxy)cyclohexylcyclopentadiene, (1.5 g, 7.28 mmol) was added to sodium hydride (0.2 g, 8.00 mmol) in THF CH-cyclohexyl); 4.09[m, 4H, 2(OCH2)]; 5.40(s, 1H, dioxanyl HC-azulene); 7.20(s, 2H, azulene H-C1,3); 7.30(d, 2H, J 10.5, (30 ml) and heated gently until the reaction had completed to give a red solution. A solution of N-butyl-4-(diethoxymethyl)- azulene H-C5,7); 8.20(d, 2H, J 10.5), azulene H-C4,8); dC (63 MHz, CD2Cl2) 14.3(q, 1C, Me), 23.1(t, 1C, CH2 ); 26.7(t, pyridinium bromide (5.0 g, 15.0 mmol) in THF (25 ml) was then added leaving a colourless solution which was heated at 1C, cyclohexyl); 27.1(t, 2C, cyclohexyl); 28.5(t, 1C, CH2); 29.7(t, 1C, CH2); 29.8[t, 7C, 7(CH2)]; 30.0(t, 1C, CH2); 30.2(t, reflux for 48 h; the reaction turning red and then dark brown. Solvent was evaporated under reduced pressure and neutral 1C, CH2); 32.3(t, 2C, cyclohexyl); 34.6(d, 1C, HC-C13H27); 40.4(d, 1C, azulene CH-cyclohexyl); 71.3[t, 2C, 2(OCH2)]; silica added to the dark brown oil.Purification by column chromatography on neutral silica using light petroleum– 105.2(d, 1C, dioxanyl HC-azulene); 116.1(d, 2C, azulene C1,3); 121.7(d, 2C, azulene C5,7); 134.1(d, 2C, azulene C4,8); 140.6(s, diethyl ether, 352, as eluent gave N-butyl-(4-ethoxycarbonyl- 4-ethyl)dihydropyridine as a colourless oil and a mixture of 2C, azulene C3a,8a); 144.7(s, 1C, azulene C6); 161.9(s, 1C, azulene C2); m/z (EI) 479 (M+, 100%).the isomers as a dark blue oil. Separation of the isomers was attempted by HPLC and reverse phase HPLC but led to 4-( Ethylenedioxy)cyclohexanol decomposition and a small amount of pure 1-[4-(ethylenedioxy) cyclohexyl]-6-(diethoxymethyl)azulene as a blue oil, 4-(Ethylenedioxy)cyclohexanone (5.0 g, 32 mmol, 1 equiv.) in (M+ Found: 370.2130, C23H30O4 calculated: 370.2144); dH dry THF (25 ml) was added dropwise to LiAlH4 (3.0 g, (250 MHz, CD2Cl2 ) 1.2 [t, 6H, J 7, 2(CH3)]; 1.85(m, 8H, 79 mmol, 2.2 equiv.) in dry THF (20 ml).When the reaction cyclohexyl); 3.23(m, 1H, azulene HC-cyclohexyl); 3.60[m, 4H, had ceased, the mixture was heated at reflux for a further 3 h 2(OCH2CH3 )]; 3.95(s, 4H, O-CH2-CH2-O); 5.4 [s, 1H, (EtO)2- and allowed to cool.Excess LiAlH4 was destroyed by the HC-azulene]; 7.25(m, 3H, azulene H-C3,5,7); 7.81(d, 1H, J 4, careful addition of wet diethyl ether and then water. The white azulene H-C2); 8.24(d, 1H, J 10, azulene H-C4); 8.33(d, 1H, J suspension was then filtered through Celite which was washed 10, azulene H-C8); dC (63 MHz, CD2Cl2) 15.3[q, 2C, with copious amounts of diethyl ether.The organic portions 2(OCH2Me)]; 32.5(t, 2C, cyclohexyl); 35.6(d, 1C, azulene CH- were combined, dried and solvent was evaporated under cyclohexyl); 62.3[t, 2C, 2(OCH2Me)]; 64.6(t, 1C, OCH2CH2- reduced pressure to leave crude 4-(ethylenedioxy)cyclohexanol O); 64.6(t, 1C, O-CH2-CH2-O); 104.9[d, 1C, (EtO)2CH-azu- as a yellow oil, 5 g, 99%, dH (250 MHz, CDCl3) 1.75(m, 8H lene]; 108.8(s, 1C, cyclohexyl-C-ketal); 117.2(d, 1C, azulene cyclohexyl CH2s); 3.80(m, 1H, HCOH); 4.00(s, 4H, ketal CH2s).C3); 120.2(d, 1C, azulene C5); 120.9(d, 1C, azulene C7); 132.5(d, 1C, azulene C2); 134.7(s, 1C, azulene C1); 135.0(d, 1C, azulene 4-( Ethylenedioxy)cyclohexyl tosylate C4); 135.9(d, 1C, azulene C8); 136.1(s, 1C, azulene C3a); 140.5(s, 1C, azulene C8a); 147.9(s, 1C, azulene C6); m/z (EI) 270 (M+, This was prepared by following the procedure of Winstein et al.12 but full experimental details are given below. 4- 50%); and 2-[4-(ethylenedioxy)cyclohexyl]-6-(diethoxymethyl)- azulene as blue microprisms, mp 53–54 °C (M+ Found: (Ethylenedioxy)cyclohexanol, (5 g, 31.6 mmol, 1 equiv.) was dissolved in dry pyridine and tosyl chloride (9.0 g, 47.2 mmol, 370.2151, C23H30O4 calculated: 370.2144); dH (250 MHz, CD2Cl2) 1.20[t, 6H, 2(OCH2Me)]; 1.80(m, 8H, cyclohexyl); 1.5 equiv.) added in small portions.The reaction mixture was stirred vigorously for 30 min and then kept at 0°C for 16 h. 2.95(m, 1H, azulene CH-cyclohexy; 3.58[m, 4H, 2(OCH2Me)]; 3.93(s, 4H, O-CH2-CH2-O); 5.42 [s, 1H, The crystals which appeared were collected and extracted into diethyl ether (50 ml).The ethereal portion was then washed (EtO)2CH-azulene]; 7.22(s, 2H, azulene H-C1,3); 7.32(d, 2H, J 10.5, azulene H-C5,7); 8.20(d, 2H, J 10, azulene H-C4,8); dC with 2 M HCl (30 ml), water (100 ml) and 10% aqueous potassium carbonate (20 ml). Solvent was evaporated under (63 MHz, CD2Cl2) 15.4[q, 2C, 2(OCH2Me)]; 31.8(t, 2C, cyclohexyl); 35.3(t, 2C, cylcohexyl); 39.1(d, 1C, azulene CH-cyclo- reduced pressure to leave a viscous oil.This was left at 0°C with seeding until crystals had formed, which were collected hexyl); 62.3[t, 2C, 2(OCH2Me)]; 64.6(t, 1C, O-CH2-CH2-O); J. Mater. Chem., 1997, 7(3), 391–401 39964.7(t, 1C, O-CH2-CH2-O); 105.0[d, 1C, (EtO)2CH-azulene]; Palladium on charcoal (75 mg) was then added and the vessel kept under an atmosphere of hydrogen.The mixture was left 108.9(s, 1C, cyclohexyl-C-ketal); 116.2(d, 2C, azulene C1,3); 122.0(d, 2C, azulene C5,7); 134.2(d, 2C, azulene C4,8); 140.5(s, stirring at 20°C until 1 equiv. of hydrogen had been taken up. The now colourless solution was filtered through Celite to 2C, azulene C3a,8a); 146.3(s, 1C, azulene C6); 160.0(s, 1C, azulene C2); m/z (EI) 370 (M+, 100%).remove the catalyst and washed with copious amounts of water. The filtrate was extracted with dichloromethane (3×60 ml) and the combined organic extracts washed with Azulene-6-carbaldehyde aq. K2CO3 (20%) and water. The organic layer was then Compound 1a (0.5 g, 2.17 mmol) was dissolved in dichloro- dried and solvent evaporated under reduced pressure to methane (100 ml) and 2 M hydrochloric acid (50 ml) added.give a slightly yellow oil which crystallised on standing. The mixture was stirred and the reaction monitored by TLC. Recrystallisation from acetone yielded 4-(4-decyloxyphenethyl)- When all the 6-(diethoxymethyl)azulene had disappeared as pyridine, as colourless crystals, 1.42 g, 94%, mp 44–45°C; dH judged by TLC, the mixture was separated and the organic (250 MHz, CDCl3) 0.90(t, 3H, Me); 1.30 [m, 14H, layer dried and the solvent evaporated under reduced pressure.CH2)2(CH2 )7Me]; 1.75 [m, 2H, CH2CH2(CH2)7Me]; 2.90(m, Recrystallisation from light petroleum gave azulene-6-carbal- 4H, CH2CH2 ); 3.90[t, 2H, CH2(CH2)8Me]; 6.75(d, 2H, dehyde as green–turquoise crystals, 0.27 g, 80%, mp 44–45 °C phenyl); 7.05(d, 2H, phenyl); 7.10(d, 2H, pyridine); 8.45(d, 2H, (M+ Found: 156.0579, C11H8O2 calculated: 156.0575); dH pyridine); dC (63 MHz, CDCl3 ) 14.1 (q, 1C, Me); 22.7(t, 1C, (250 MHz, CDCl3) 7.50(d, 2H, J 3.5, azulene H-C1,3); 7.70(d, CH2); 26.1(t, 1C, CH2); 29.3[t, 2C, (CH2)2]; 29.4(t, 2C, 2CH2 ); 2H, J 10, azulene H-C5,7); 8.10(t, 1H, J 3.5, azulene H-C2); 29.6(t, 1C, CH2); 31.9(t, 1C, CH2); 35.7(t, 1C, phenyl-CH2- 8.50(d, 2H J 10, azulene H-C4,8); 10.1 (s, 1H, CHO); dC CH2); 37.3(t, 1C, CH2-CH2-pyridine), 68.0(t, 1C, OCH2 ); (63 MHz, CDCl3) 119.8 (d, 2C, azulene C1,3); 123.7(d, 2C, 114.5(d, 2C, phenyl); 124.0(d, 2C, pyridine); 129.3(d, 2C, azulene C5,7); 135.2 (d, 2C, azulene C4,8); 137.1(s, 1C, azulene phenyl); 132.5(s, 1C, phenyl); 149.5(d, 2C, pyridine); 150.8(s, C2); 140.3(s, 2C, azulene C3a,8a); 141.7(s, 1C, azulene C6); 1C, phenyl); 157.6(s, 1C, pyridine); m/z (EI) 339 (M+, 15%). 194.6(d, 1C, CHO); m/z (EI) 156 (M+, 100%). N-Butyl-4-(4-decyloxyphenethyl )pyridinium bromide 6-(4-Hexyloxyphenethyl ) azulene, 2a 4-(4-Decyloxyphenethyl)pyridine (2.7 g, 7.96 mmol) was dis- Diethyl 4-(hexyloxybenzyl)phosphonate (1.00 g, 2.96 mmol) solved in absolute ethanol (30 ml) and 1-bromobutane (4 g, was dissolved in diethyl ether (30 ml) and potassium tert- 29.1 mmol, excess) added.The mixture was heated at reflux butoxide added (0.33 g, 2.96 mmol) to give a yellow precipitate. for 50 h and allowed to cool at which pale yellow crystals When this had dissolved azulene-6-carbaldehyde was added. appeared in the yellow solution.Excess 1-bromobutane The reaction was then kept stirring at 20°C in the dark and and ethanol were evaporated under reduced pressure and followed by TLC. After 30 min the aldehyde spot seemed drying under high vacuum then gave crude yellow crystals, to have disappeared and an upper green spot appeared. found by 1H NMR spectroscopy to be mainly N-butyl-4-(4- Purification was attempted by column chromatography on decyloxyphenethyl)pyridinium bromide, 2.26 g, 60%; dH silica using hexane–CH2Cl2, 352, as eluent in the dark to give (250 MHz, CDCl3) 0.80(t, 3H, Me); 0.95(t, 3H, Me); 1.25(m, a green crystalline product of 6-(4-hexyloxystyryl)azulene, 16H, OC2H4C7H14Me, NC2H4CH2Me); 1.75(m, 2H, which rapidly decomposed on standing, mp 225 °C (decomp.), OCH2CH2C8H17); 2.00(m, 2H, NCH2CH2C2H4); 2.95(t, 2H, dH (250 MHz, CDCl3) 0.90 (t, 3H, J 7, Me); 1.40[m, 6H, phenyl-CH2-CH2-pyridine); 3.2(t, 2H, phenyl-CH2-CH2-pyri- CH2(CH2)3Me]; 1.80(m, 2H, CH2CH2C4H9); 3.99(t, 2H, J 7, dine); 3.90(t, 2H, OCH2C9H19); 4.90(t, 2H, NCH2C3H7 ); CH2C5H11); 6.92(d, 2H, J 9, phenyl); 7.18(s, 2H, -CHNCH-); 6.75(d, 2H, phenyl); 7.00(d, 2H, phenyl); 7.80(d, 2H, pyridine); 7.32(d, 2H, J 4, azulene H-C1,3 ); 7.4(d, 2H, J 11, azulene H- 9.20(d, 2H, pyridine); m/z (EI) C27H42ON 396 (M+-Br, 50%).C5,7); 7.5(d, 2H, J 9, phenyl); 7.8(t, 1H, J 4, azulene H-C2); A less soluble product was isolated after extraction of the 8.30(d, 2H, J 11, azulene H-C4,8); m/z (EI) 330 (M+, 100%). crude yellow crystals with dry acetone, which gave cream This green product was then taken up into dry THF (30 ml) crystals, and these were determined to be pure 4-(4-decyloxy- and lithium aluminium hydride added carefully (0.2 g, phenethyl)pyridinium bromide (Found: C, 65.71; H, 7.99; N, 4.93 mmol); the mixture was heated at reflux for 3 h, then 3.43; Br, 18.89: C23H34NOBr calculated: C, 65.71; H, 8.15; N, stirred for 16 h at 20°C.An upper purple spot was observed 3.33; Br, 19.01); dH (250 MHz, CDCl3 ) 0.80(t, 3H, Me); 1.25 on TLC. The solvent was evaporated under reduced pressure (m, 14H, OC2H4C7H14Me); 1.70(m, 2H, OCH2CH2C8H17); and then purification was attempted by column chromatogra- 2.90(t, 2H, phenyl-CH2-CH2-pyridine); 3.15(t, 2H, phenyl- phy on silica, using CH2Cl2–hexane, 253, as eluent, to give 6- CH2-CH2-pyridine); 3.85(t, 2H, OCH2C9H19); 6.75(d, 2H, (4-hexyloxyphenethyl)azulene as purple microprisms, which phenyl); 6.90(d, 2H, phenyl); 7.65(d, 2H, pyridine); 8.70(d, 2H, were then recrystallised from hexane, 0.10 g, 15%, mp 105 °C; pyridine); dC (63 MHz, CDCl3) 14.1(q, 1C, Me); 22.7(t, 1C, dH (250 MHz, CDCl3 ) 0.9(t, 3H, J 7, Me); 1.3[m, 6H, CH2); 26.0(t, 1C, CH2); 29.3(t, 1C, CH2); 29.4(t, 2C, 2CH2 ); (CH2 )2(CH2)3Me]; 1.80(m, 2H, CH2CH2C4H9); 3.0(m, 4H, 29.5(t, 2C, 2CH2); 31.9(t, 1C, CH2); 35.0(t, 1C, phenyl-CH2- CH2CH2); 3.90(t, 2H, J 7, CH2C5H11); 6.7(d, 2H, J 9, phenyl); CH2); 38.3(t, 1C, CH2-CH2-pyridine); 68.1(t, 1C, OCH2 ); 7.05(d, 2H, J 11, azulene H-C5,7); 7.05(d, 2H, J 9, phenyl); 114.8(d, 2C, phenyl CH); 127.2(d, 2C, pyridine); 129.3(d, 2C, 7.30(d, 2H, J 4, azulene H-C1,3); 7.80(t, 1H, J 4, azulene H- phenyl); 130.0(s, 1C, phenyl); 140.0(d, 2C, pyridine); 158.1(s, C2); 8.20(d, 2H, J 11, azulene H-C4,8); dC (63 MHz, CDCl3); 1C, phenyl); 163.3(s, 1C, pyridine); m/z (EI) C23H34ON 340 14.0 (q, 1C, Me); 22.6(t, 1C, CH2); 25.7(t, 1C, CH2); 29.3(t, (M+-Br, 100%). 1C, CH2); 31.6(t, 1C, CH2 ); 38.0(t, 1C, CH2); 44.6(t, 1C, CH2); 68.1(t, 2C, CH2CH2); 114.5(d, 2C, phenyl); 117.9(d, 2C, azulene 6-(4-Decyloxyphenethyl) azulene, 2b C1,3); 124.1(d, 2C, phenyl); 129.4(d, 2C, azulene C5,7); 133.0(s, Freshly distilledcyclopentadiene (2.00 g, 30.3 mmol) was added 1C, phenyl); 135.8(d, 1C, azulene C2); 135.9(d, 2C, azulene dropwise over 30 min to sodium hydride (0.75 g, 24.6 mmol) C4,8); 138.9(s, 2C, azulene C3a,8a); 152.5(s, 1C, phenyl); 157.6(s, in THF (70 ml) at 0°C and the mixture was then allowed to 1C, azulene C6); m/z (EI) 332 (M+, 15%).warm to 20°C. N-Butyl-4-(4-decyloxyphenethyl)pyridinium bromide (5.36 g, 11.3 mmol) dissolved in dry THF (10 ml) was 4-(4-Decyloxyphenethyl ) pyridine then added to the pink solution which turned red, then green, then blue, and finally brown.The mixture was heated at reflux trans-4-Decyloxy-4¾-stilbazole19 (1.5 g, 4.45 mmol) was dissolved in glacial acetic acid (100 ml) to give a yellow solution. for 90 h, a blue spot being indicated by TLC. THF was 400 J. Mater. Chem., 1997, 7(3), 391–401evaporated under reduced pressure to leave a brown oil. Silica References was added to the brown oil and purification by column 1 M. R. Churchill, in Progress in Inorganic Chemistry, ed. chromatography using light petroleum (bp 40–60 °C) as eluent, S. J. Lippard, vol. 11, pp. 58–59. gave a blue product. Recrystallisation from diethyl ether– 2 E.W. Thulstrup, P. L. Case and J. Michl, Chem. Phys., 1974, 6, 410. methanol gave 6-(4-decyloxyphenethyl)azulene as blue crys- 3 K. Praefcke and D. Schmidt, Z. Naturforsch., T eil B, 1981, 34, 375. 4 T. Nozoe, S. Matsumaru, Y. Murase and S. Seto, Chem. Ind., 1955, tals, 0.64 g, 15%, mp 100°C, (Found: C, 86.55, H, 9.38; C28H36O 1257. calculated: C, 86.55; H, 9.33%); dH (250 MHz, CD2Cl2) 0.9(t, 5 R. Brettle, D. A. Dunmur, S. E. Estdale and C. M. Marson, 3H, J 7, Me); 1.3[m, 14H, (CH2)2(CH2)7Me]; 1.80(m, 2H, J. Mater. Chem., 1993, 3, 327. CH2CH2C8H17); 3.0(m, 4H, CH2CH2); 3.90(t, 2H, J 7, 6 T. Morita, K. Takase and M. Kaneko, Jpn. Pat. 0269439, 1990. CH2C9H19); 6.75(d, 2H, J 9, phenyl); 7.05(d, 2H, J 11, azulene 7 T. Morita, K. Takase and M. Kaneko, Jpn. Pat. 0269436, 1990. 8 T. Morita, K. Takase and M. Kaneko, Jpn. Pat. 0269438, 1990. H-C5,7 ); 7.05(d, 2H, J 9, phenyl); 7.30(d, 2H, J 4, azulene H- 9 T. Morita, K. Takase and M. Kaneko, Jpn. Pat. 0269437, 1990. C1,3); 7.80(t, 1H, J 4, azulene H-C2); 8.25(d, 2H, J 11, azulene 10 T. Morita, K. Takase and M. Kaneko, Jpn. Pat. 0269441, 1990. H-C4,8); dC (63 MHz, CD2Cl2); 14.3 (q, 1C, Me); 23.1(t, 1C, 11 K. Hafner, Angew. Chem., 1957, 69, 393. CH2); 26.5(t, 1C, CH2); 29.8(t, 1C, CH2); 30.0[t, 2C, (CH2)2]; 12 E. Bernaert, M. Anteumis and D. Tavernier, Bull. Soc. Chim. Belg., 32.3(t, 1C, CH2); 38.3(t, 1C, CH2); 44.9(t, 1C, CH2); 68.5(t, 1974, 83, 357. 2C, CH2CH2); 114.8(d, 2C, phenyl); 118.2(d, 2C, azulene C1,3); 13 T. Koenig, K. Rudolf, R. Chadwick, H. Geiselmann, T. Patapoff and C. E. Klopfenstein, J. Am. Chem. Soc., 1986, 108, 5024. 124.5(d, 2C, phenyl); 129.8(d, 2C, azulene C5,7); 133.5(s, 1C, 14 R. Luhowy and P. M. Keehn, J. Am. Chem. Soc., 1977, 99, 3797. phenyl); 136.1(d, 1C, azulene C2); 136.3(d, 2C, azulene C4,8); 15 K. J. Toyne, T hermotropic liquid crystals, ed. G. W. Gray, Wiley, 139.3(s, 2C, azulene C3a,8a); 153.1(s, 1C, phenyl); 158.1(s, 1C, Chichester, 1987, p. 41. azulene C6); m/z (EI) 388 (M+, 20%). 16 E. M. Averyanov, V. M. Muratov and V. G. Rumyantsev, Sov. Phys., 1985, 61, 476. 17 F. Popp and W. McEwen, J. Am. Chem. Soc., 1958, 80, 1181. 18 E. Cesarotti and H. B. Kagan, J. Organomet. Chem., 1978, 162, 297. We are grateful to Hitachi Limited for financial support, and 19 D. W. Bruce, D. A. Dunmur, E. Lalinde, P. M. Maitlis and to Dr K. Toriyama for discussion. The assistance of Dr G. P. Styring, L iq. Cryst., 1988, 3, 385. Ungar in making X-ray measurements is also gratefully acknowledged. Paper 6/06139G; Received 6th September, 1996 J. Mater. Chem., 1997, 7(3), 391–401 401

ISSN:0959-9428    

DOI:10.1039/a606139g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Cyclopalladated acac and cp liquid crystals: a comparative study Donocadh P. Lydon, Gareth W. V. Cave and Jonathan P. Rourke*† Department of Chemistry, Warwick University, Coventry, UK CV4 7AL The cyclopalladation of mesogenic Schiff bases yields two series of novel metallomesogens. The flat acetylacetonate derivatives show both nematic and smectic A phases with extended mesogenic ranges. In contrast, the non-planar cyclopentadienyl complexes show nematic phases at much lower temperatures than those of the acetylacetonate complexes.There is currently much interest in the synthesis of metal- and the clearing points are essentially the same. The fact that acac complexes do not exhibit the more ordered smectic phases containing liquid crystals owing to the perceived advantages of combining the properties of liquid crystal systems with those shown by the ligands is not surprising when one considers that the shape of the complexes will be distorted away from of transition metals.The area has been well reviewed recently,1–5 with excellent new work appearing constantly.6–11 the calamitic shape of the ligand by the presence of the Pd(acac) moiety on the side. Presumably this group disrupts Cyclopalladated compounds have proved to be a particularly fertile area of research, with many different examples from the packing of the molecule within the crystal, resulting in the lower melting point of the complexes compared with the many different groups.10,12–22 We have been studying a number of cyclopalladated Schiff ligands.The absence of a nematic phase for compound 3d is not unexpected given the presence of the two long chains base compounds with two very different co-ligands and present our results here.(seven carbons) at either end of the molecule, which presumably stabilise the smectic phase. It is interesting to note that the clearing points of complexes 3a and 3b, which both have four Synthesis carbons on the biphenyl group, are very similar, as are those of 3c and 3d, which both have seven carbons. It is also The synthesis of the new compounds described here, 3 and 5, interesting to note that the stability of the smectic phase seems is summarised in Scheme 1.The synthesis of the 4-alkyloxy- to be related to the length of the chain on the cyclopalladated N-(4¾-alkyloxybiphenyl)benzylidene ligands 1 via a simple con- ring.Thus, complexes 3b and 3d, which both have seven densation of the appropriate aldehyde and aniline proceeded carbons on the cyclopalladated ring, locating the bulky in high yield. The cyclopalladation step to give the intermediate Pd(acac) moiety more towards the centre of the molecule. have 2 was essentially quantitative, and 2 was used without further the most stable smectic A phases.purification. The synthesis of the acetylacetonate (acac) deriva- The thermal behaviour of the cp complexes 5 is listed in tives 3 from 2 proceeded in good yield, and these complexes Table 1 and summarised in Fig. 1. Thus, all the complexes were purified by column chromatography. The synthesis of the showed only a nematic phase, with the exception of 5d, which cyclopentadienyl (cp) complexes 5 from 2 via 4 gave a poor exhibits a smectic A phase too.The phases were identified on yield overall, after purification. All homologues of compounds the basis of their optical texture, the nematic and smectic A 1, 3 and 5 were analysed by 1H and 13C NMR and gave good phases exhibiting classic textures.The melting and clearing elemental analyses (see Table 2, later). points of complexes 5 are much lower than those of both the ligands 1 and the acac complexes 3. The fact that cp complexes Thermal properties do not exhibit the more ordered smectic phases is not surprising when one considers the shape of the complexes. Whilst both The thermal behaviour of the ligands 1 is listed in Table 1 and the ligands and the acac complexes can be thought of as summarised in Fig. 1. Thus, all the ligands showed smectic F, essentially planar, the cp ring is perpendicular to the plane of smectic C and nematic phases before clearing. The phases were the ligand. Clearly this group disrupts the packing of the identified on the basis of their optical texture, the nematic and molecule within the crystal, resulting in the reduced melting smectic C phases exhibiting schlieren textures, the nematic and clearing points of the complexes and the destabilisation showing both four- and two-point brushes, the smectic C only of the smectic phases.The presence of a smectic phase for four-point brushes. The smectic F phase showed a schlieren- compound 5d is not surprising given the presence of the two mosaic type texture on cooling from the smectic C phase.The long chains (seven carbons) at either end of the molecule, and absence of any point disclinations allowed us to distinguish it this mirrors the behaviour of the acac complex 3d. It is from the smectic I phase. interesting to note that the melting points of complexes 5a The thermal behaviour of the acac complexes 3 is listed in and 5c, which both have four carbons on the cyclopalladated Table 1 and summarised in Fig. 1. Thus, all the complexes ring, are very similar, as are those of 5b and 5d, which both showed a smectic A phase and, with the exception of 3d, a have seven, and thus the bulky Pd(cp) moiety located more nematic phase before clearing. The phases were identified on towards the centre of the molecule.the basis of their optical texture. The smectic A phase appeared Compounds 5 decompose at ca. 180 °C on transition to the as a focal-conic fan texture which separated on cooling from isotropic liquid, whereas compounds 3 do not decompose at the isotropic as batonnets which consisted of growing focal- temperatures almost 100 K higher. Chemically, the major conic domains.The melting and clearing points of complexes difference between the two complexes is the electron count on 3 neatly mirror those of the ligands from which they are the palladium: the cp complex has a formal count of 18e-, derived: the melting points of complexes 3 are ca. 10 K lower, whereas the acac complex has one of 16e-. The geometry of the cp complex is formally trigonal bipyramidal, whilst that of the acac complex is square planar. The chemistry of pal- † Email: j.rourke@warwick.ac.uk J.Mater. Chem., 1997, 7(3), 403–406 403N CnH2 n+1O OCmH2m+1 N OCnH2n+1 CmH2m+1O N CnH2 n+1O OCmH2m+1 Pd Pd OAc AcO N CnH2 n+1O OCmH2m+1 Pd O O N OCnH2n+1 CmH2m+1O N CnH2 n+1O OCmH2m+1 Pd Pd Cl Cl N CnH2 n+1O OCmH2m+1 Pd 1 NaAcac Pd(OAc)2 3 Tl(C5H5) 4 5 HCl 2 a n = 4, m = 4 b n = 4, m = 7 c n = 7, m = 4 d n = 7, m = 7 Scheme 1 ladium(II) is dominated by square-planar 16e- species, with exhibit mesogenic behaviour, with both smectic A and nematic phases being observed.very few examples of 18e- complexes. Thus the observed Thus it can be seen that our results are consistent with thermal stabilities of our compounds are entirely reasonable. established precedent: compared with the acac group, the cp Compounds 5 represent the only isomerically pure halfgroup brings down both the melting and clearing points of the sandwich liquid crystals ever reported.The only other halfcomplexes and shows a strong preference for the nematic sandwich liquid crystals known are those reported by Ghedini phase.It is clear that the cp group will become a popular et al.,10 where an azobenzene cyclometallates to give two motif in metallomesogen chemistry. isomeric products. Ghedini’s compounds, which like ours contain three aromatic rings, only exhibited nematic phases and at very similar temperatures to ours. Ghedini et al. also Experimental synthesised a couple of compounds with only two aromatic General rings, but observed no mesogenic behaviour for these cp derivatives.In contrast, some earlier work by Espinet et al.14 All chemicals were used as supplied, unless noted otherwise. All NMR spectra were obtained on either a Bruker AC250 or had shown that the acac derivatives of a two-ring system did 404 J. Mater. Chem., 1997, 7(3), 403–406Table 1 Mesogenic behaviour of compounds 1, 3 and 5 compd. trans.T/°C trans. T/°C trans. T/°C trans. T/°C 1a C–SF 191 SF–SC 197 SC–N 201 N–I 272 1b C–SF 160 SF–SC 171 SC–N 216 N–I 252 1c C–SF 171 SF–SC 178 SC–N 215 N–I 255 1d C–SF 157 SF–SC 161 SC–N 217 N–I 254 3a C–SA 184 SA–N 209 N–I 260 3b C–SA 162 SA–N 241 N–I 261 3c C–SA 155 SA–N 225 N–I 249 3d C–SA 141 SA–I 245 5a C–N 125 N–I 182a 5b C–N 101 N–I 145 5c C–N 125 N–I 179a 5d C–SA 92 SA–N 165 N–I 178a *Some decomposition.on an AC400 in CDCl3 and are referenced to external SiMe4, Hn ] , 1.81 (4 H, m, Ho,o¾), 1.40 (16 H, m, Hp,p¾), 0.89 [6 H, t, 3J(HH) 7.0 Hz, Hq,q¾]; dC: 159.2 (Ca), 158.5 (Ce,m ), 138.1 (Ci), assignments being made with the use of decoupling, NOE and the DEPT and COSY pulse sequences. Thermal analyses were 132.9 (Cb/j), 130.5 (Cc), 127.7 (Ch), 127.2 (Ck), 121.2 (Cg), 114.7 (Cd/l), 114.6 (Cd/l), 68.0 (Cn), 67.8 (Cn¾), 31.7 (Cp,p¾), 29.1 (Co,o¾), performed on an Olympus BH2 microscope equipped with a Linkam HFS 91 heating stage and a TMS90 controller, at a 28.9 (Cp,p¾), 25.9 (Cp,p¾), 19.2 (Cp,p¾), 14.0 (Cq,q¾).The mesogenic behaviour of all homologues is summarised heating rate of 10 K min-1.All elemental analyses were performed by Warwick Microanalytical Service. in Fig. 1 and detailed in Table 1. Elemental analyses are detailed in Table 2. Preparation of 4-heptyloxy-N-(4¾-heptyloxybiphenyl) benzylidene, 1d Preparation of orthometallated palladium acetate complex, 2d Compound 2d is described in detail, all other homologues Compound 1d is described in detail, all other homologues were prepared similarly. 4-Heptyloxybenzaldehyde (1.61 g, were prepared similarly. Ligand 1d, (0.41 g, 8.5×10-4 mol) and palladium acetate (0.191 g, 8.5×10-4 mol) were dissolved 7.10×10-3 mol) was added to a solution of 4¾-heptyloxy-4- aminobiphenyl (2.00 g, 7.10×10-3 mol) in toluene (200 ml). in acetic acid (250 ml) at 60°C, and stirred (20 h). The solvent was removed, the crude product dissolved in chloroform, The mixture was heated at reflux for 2 h using a Dean Stark trap and in the presence of molecular sieves.The solvent was filtered to remove traces of palladium black and the yellow solution evaporated to dryness. Yield 0.55 g (98%, removed and the product recrystallised from chloroform. Yield 2.47 g (72%, 5.1×10-3 mol). 4.2×10-4 mol).NMR data: dH: 8.44 (1 H, s, Ha), 7.87 (2 H, AA¾XX¾, Hc), 7.57 (2 H, AA¾XX¾, Hh ) , 7.55 (2 H, AA¾XX¾, Hk ) , 7.28 (2 H, NMR data: dH: 7.59 (1 H, s, Ha), 7.51 (2 H, AA¾XX¾, Hm), AA¾XX¾, Hg ) , 6.96 (2 H, AA¾XX¾, Hd), 6.95 (2 H, AA¾XX¾, Hl), 7.35 (2 H, AA¾XX¾, Hj), 7.18 [1 H, d, 3J(HH) 8.4 Hz, Hg], 6.95 4.03 [2 H, t, 3J(HH) 7.0 Hz, Hn¾], 4.01 [2 H, t, 3J(HH) 7.0 Hz, (2 H, AA¾XX¾, Hn ) , 6.78 (2 H, AA¾XX¾, Hi ) , 6.59 [1 H, dd, 3J(HH) 8.4 Hz, 4J(HH) 2.3 Hz, Hf], 6.03 [1 H, d, 4J(HH) 2.3 Hz, Hd], 4.05 [2 H, t, 3J(HH) 6.4 Hz, Hp¾], 4.00 [2 H, t, 3J(HH) 6.7 Hz, Hp], 1.90 (3H, s, Ht), 1.81 (4 H, m, Hq,q¾), 1.40 (16 H, m, Hr,r¾), 0.88 [6 H, t, 3J(HH) 7.1 Hz, Hs,s¾].Table 2 Elemental analysis data for compounds 1, 3 and 5 found (expected) compd. n m C (%) H (%) N (%) 1a 4 4 80.9 (80.8) 7.8 (7.8) 3.4 (3.5) 1b 4 7 81.2 (81.2) 8.4 (8.4) 3.1 (3.2) 1c 7 4 81.6 (81.2) 8.4 (8.4) 3.2 (3.2) 1d 7 7 81.3 (81.6) 8.7 (8.9) 3.0 (2.9) 3a 4 4 63.4 (63.4) 6.2 (6.2) 2.3 (2.3) 3b 4 7 64.5 (64.9) 6.6 (6.7) 2.0 (2.2) 3c 7 4 64.7 (64.9) 6.7 (6.7) 2.3 (2.2) 3d 7 7 66.3 (66.0) 7.2 (7.3) 1.9 (2.0) 5a 4 4 69.9 (67.2) 6.2 (6.2) 2.4 (2.5) 5b 4 7 68.1 (68.5) 6.6 (6.7) 2.1 (2.3) 5c 7 4 68.2 (68.5) 6.9 (6.7) 2.2 (2.3) 5d 7 7 69.5 (69.6) 7.6 (7.2) 2.2 (2.1) Fig. 1 Phase behaviour of compounds 1, 3 and 5 J. Mater. Chem., 1997, 7(3), 403–406 405Preparation of palladium acetylacetonate complex, 3d NMR data: dH: 7.86 (1 H, s, Ha), 7.54 (4 H, m, Hi,m ), 7.52 [1 H, d, 3J(HH) 8.4 Hz, Hg], 7.35 (2 H, AA¾XX¾, Hj ) , 7.24 Compound 3d is described in detail, all other homologues [1 H, d, 4J(HH) 2.3 Hz, Hd], 6.97 (2 H, AA¾XX¾, Hn ) , 6.59 were prepared similarly.Sodium acetylacetonate (0.038 g, [1 H, dd, 3J(HH) 8.4 Hz, 4J(HH) 2.3 Hz, Hf], 5.80 (5 H, s, 3.08×10-4 mol) was added to a solution of the acetate bridged Ht), 4.02 [2 H, t, 3J(HH) 6.9 Hz, Hp¾], 4.01 [2 H, t, 3J(HH) palladium complex 2d (0.200 g, 1.54×10-4 mol) in acetone 6.9 Hz, Hp], 1.84 (4 H, m, Hq,q¾), 1.40 (16 H, m, Hr,r¾), 0.90 (150 ml) at room temperature and stirred (2 h).The solvent [6 H, t, 3J(HH) 8.2 Hz, Hs,s¾]; dC: 164.3 (Ca), 158.9 (Ce), 157.7 was removed and the product was purified by column chroma- (Co), 139.6 (Cb/c/h), 138.9 (Cb/c/h), 138.4 (Cb/c/h), 138.1 (Cb/c/h), tography on silica, eluting with a 50550 mixture of dichloro- 132.4 (Ck), 131.8 (Cg), 130.5 (Cl), 128.0 (Cj/m), 127.9 (Cj/m ), methane and hexane.Yield 0.135 g (64%, 1.96×10-4 mol). 125.6 (Cd), 123.0 (Ci), 114.8 (Cn), 110.5 (Cf), 95.8 (Ct), 68.0 (Cp), 67.8 (Cp¾), 31.8 (Cq), 31.3 (Cq¾), 29.2 (Cr,r¾), 26.0 (Cr), 19.2 (Cr,r¾), 14.1 (Cs/s¾), 13.9 (Cs/s¾). The mesogenic behaviour of all homologues is summarised in Fig. 1 and detailed in Table 1. Elemental analyses are detailed in Table 2.We thank the University of Warwick for financial support NMR data: dH: 8.03 (1 H, s, Ha), 7.58 (2 H, AA¾XX¾, Hj), (D.P.L.), and Johnson-Matthey for loan of chemicals. 7.51 (2 H, AA¾XX¾, Hm), 7.46 (2 H, AA¾XX¾, Hi), 7.31 [1 H, m, 3J(HH) 8.1 Hz, Hg], 7.14 [1 H, d, 4J(HH) 2.3 Hz, Hd], 6.97 [2 H, AA¾XX¾, 3J(HH) 8.4 Hz, Hn], 6.60 [1 H, dd, 3J(HH) 8.3 Hz, 4J(HH) 2.3 Hz, Hf], 5.36 (1 H, s, Hv), 4.08 [2 H, t, References 3J(HH) 6.5 Hz, Hp¾], 4.02 [2 H, t, 3J(HH) 6.5 Hz, Hp], 2.10 (3H, s, Hx), 1.91 (3H, s, Ht), 1.84 (4 H, m, Hq,q¾), 1.40 (16 H, 1 S.A. Hudson and P. M. Maitlis, Chem. Rev., 1993, 93, 861. m, Hr,r¾), 0.90 [6 H, t, 3J(HH) 8.2 Hz, Hs,s¾]; dC: 188.3 (Cu/w), 2 A-M. Giroud-Godquin and P. M. Maitlis, Angew. Chem., Int.Ed. Engl., 1991, 30, 375. 185.7 (Cu/w), 172.4 (Ca), 160.4 (Ce), 158.7 (Co), 146.3 (Ch), 139.7 3 P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and E. Sola, (Cb/c), 138.8 (Cb/c), 132.6 (Ck), 129.5 (Cg), 127.9 (Cm), 127.6 Coord. Chem. Rev., 1992, 117, 215. (Cl), 126.5 (Cj), 123.6 (Ci ), 115.7 (Cd), 114.7 (Cn), 111.4 (Cf), 4 D. W. Bruce, in Inorganic Materials, ed. D. W. Bruce and D. 100.1 (Cv), 67.7 (Cp), 67.5 (Cp¾), 31.2 (Cq,q¾), 31.1 (Cq,q¾), 29.2 O’Hare, Wiley, Chichester, 1992. (Cr,r¾), 27.8 (Ct), 27.4 (Cx), 25.9 (Cr,r¾), 19.1 (Cr,r¾), 13.8 (Cs,s¾). 5 A. P. Polishchuk and T. V. Timofeeva, Russ. Chem. Rev., 1993, The mesogenic behaviour of all homologues is summarised 62, 291. in Fig. 1 and detailed in Table 1. Elemental analyses are 6 A. Omenat and M.Ghedini, J. Chem. Soc., Chem. Commun., 1994, 1309. detailed in Table 2. 7 R. Ishii, T. Kaharu, N. Pirio, S-W. Zhang and S. Takahashi, J. Chem. Soc., Chem. Commun., 1995, 1215. Preparation of chloro-bridged palladium complex, 4d 8 J. P. Rourke, D. W. Bruce and T. B. Marder, J. Chem. Soc., Dalton T rans., 1995, 317. Compound 4d is described in detail, all other homologues 9 R. Deschenaux, I.Kosztics and B. Nicolet, J. Mater. Chem., 1995, were prepared similarly. One equivalent of 0.4 mol dm-3 5, 2291. methanolic hydrogen chloridewas added to the acetato bridged 10 M. Ghedini, D. Pucci and F. Neve, Chem. Commun., 1996, 137. palladium complex 2d, (0.356 g, 3.1×10-4 mol) dissolved 11 R. Deschenaux, M. Schweissguth and A-M. Levelut, Chem. in chloroform (250 ml) at room temperature causing the Commun., 1996, 1275.clear yellow solution to become cloudy. The solvent was 12 J. Barbera�, P. Espinet, E. Lalinde, M. Marcos and J. L. Serrano, L iq. Cryst., 1987, 2833. removed and the crude product was washed with acetone 13 P. Espinet, J. Pe�rez, M. Marcos, M. B. Ros, J. L. Serrano, (15 ml) and filtered to collect the product. Yield 0.21 g (54%, J.Barbera� and A. M. Levelut, Organometallics, 1990, 9, 2028. 1.72×10-4 mol). 14 M. J. Baena, P. Espinet, M. B. Ros and J. L. Serrano, Angew. Chem., Int. Ed. Engl., 1991, 30, 711. Preparation of palladium cyclopentadienyl complex, 5d 15 M. J. Baena, J. Barbera�, P. Espinet, A. Ezcurra, M. B. Ros and J. L. Serrano, J. Am. Chem. Soc., 1994, 116, 1899. Compound 5d is described in detail, all other homologues 16 M.Ghedini, S. Morrone, O. Francescangeli and R. Bartolino, were prepared similarly. Thallium cyclopentadienide (0.200 g, Chem. Mater., 1992, 4, 1119. 7.64×10-4 mol, 4 equiv.) was added to a solution of 17 M. Ghedini, S. Morrone, O. Francescangeli and R. Bartolino, the chloro-bridged palladium complex 4d (0.239 g, Chem. Mater., 1994, 6, 1971. 18 M. Ghedini, D. Pucci, N. Scaramuzza, L. Komitov and S. T. 1.91×10-4 mol) in THF (250 ml) and heated at reflux (1 h). Lagerwall, Adv. Mater., 1995, 7, 659. The mixture was filtered and the solvent removed. The crude 19 L. Zhang, D. Huang, N. Xiong, J. Yang, G. Li and N. Shu, Mol. product was purified by column chromatography on silica, Cryst., L iq. Cryst., 1993, 237, 285. eluting with chloroform to yield a red solid. Yield 0.040 g 20 N. Hoshino, H. Hasegawa and Y. Matsunaga, L iq. Cryst., 1991, (28%, 5.16×10-5 mol). 9, 267. 21 M. Marcos, J. L. Serrano, T. Sierra and M. J. Gime�nez, Chem. Mater., 1993, 5, 1332. 22 K. Praefcke, S. Diele, J. Pickardt, B. Gu�ndogan, U. Nu�tz and D. Singer, L iq. Cryst., 1995, 18, 857. Paper 6/05791H; Received 20th August, 1996 406 J. Mater. Chem., 1997, 7(3), 4

ISSN:0959-9428    

DOI:10.1039/a605791h

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Devil’s staircase between antiferroelectric SCA* and ferroelectric SC* phases in liquid crystals observed in free-standing films under temperature gradients Keizo Itoh,a Masaaki Kabe,b Kouichi Miyachi,b Yoichi Takanishi,b Ken Ishikawa,b Hideo Takezoeb and Atsuo Fukuda*b aKashima Oil Co. L td., R & D Department, T owada, Kamisu-machi, Kashima-gun, Ibaraki 314-02, Japan bT okyo Institute of T echnology, Department of Organic and Polymeric Materials, O-okayama,Meguro-ku, T okyo 152, Japan By studying the electro-optical properties and the textures of the subphases successively emerging between antiferroelectric SCA* and ferroelectric SC* (the Devil’s staircase), we have revealed several interface effects in both homogeneous and homeotropic cells; free-standing films are most suitable for making observations almost free from the effects.By applying appropriate temperature gradients to the free-standing films, we can directly see any part of the subphase sequence in the visual field of an optical microscope. The two ferrielectric subphases on the low- and high-temperature sides of ferrielectric SCc* together with another ferrielectric subphase between the antiferroelectric subphase (designated as AF in ref. 9) and SC* were thus confirmed to exist definitely.We have discussed the origin of these successive subphases in terms of the several theoretical models reported so far, concluding that the ANNNI model with the third-nearest-neighbour interaction well describes their Devil’s staircase character. Various tilted, chiral, fluid smectic (SC*-like) phases have been Among these subphases, SCa* is quite different from the other ones between SCA* and SC* in the sense that it is located found in antiferroelectric liquid crystals,1,2 which are shown in Scheme 1 in increasing order of temperature; some of the above SC*.In previous papers,2,22–24 we reported that SCa* forms not only the electric-field-induced staircase, SCa* (qE), phases may not actually occur but, when they do exist, they follow this order in almost all the compounds and mixtures but also the temperature-induced one, SCa* (qT).However, the staircase characters are not so typical to allow us meaningful investigated so far.1–25 The SCA* and SC* phases are the fundamental ones and the others between them, together with comparison between theory and experiment.We have also conjectured that the subphases emerging between SCA* and SCa*, are the subphases. Ferrielectric SCc* and antiferroelectric AF phases seem to be secondarily fundamental.8–11 On the SC* form another temperature-induced staircase describable by the one-dimensional Ising model with long-range repulsive high- and low-temperature sides of SCc*, there may emerge ferrielectric FIH and FIL phases, respectively.8–11 The existence interactions.2,8–11,26–28 Since some other theoretical explanations have also been published,29–53 it is appropriate to of FI, another ferrielectric subphase between AF and SC*, was reported recently by Hatano et al.13 and O’Sullivan et al.21 investigate the subphases experimentally in more detail and to examine the applicability of the proposed theoretical models.Isozaki et al.9 insisted that a few additional subphases seem to emerge in the vicinity of FIH and FIL. Likewise,some subphases We expect that this staircase will appear much more typical so that the investigation and the examination will be performed other than FI are expected in the temperature region between AF and SC*.Consequently, we designated these regions as practically, if thick free-standing films54–56 of suitable materials are prepared carefully. The purposes of this paper are: (1) to spr1, spr2 and spr3, respectively, where spr refers to subphase region. establisha convenient method of studying the staircase between SCA* and SC*; (2) to introduce some suitable materials which There are three factors that may apparently confuse the above sequence.First, the rather stable antiferroelectric AF allow us to characterize unambiguously the subphases in the regions spr3, spr2 and spr1; (3) to discuss the origin of the phase appearing in addition to SCA* may cause inappropriate identification of AF to SCA*. Secondly, ferroelectric tilted staircase in terms of the several theoretical models so far proposed; and (4) to conclude that the ANNNI model hexatic SI* below SCA* may cause inappropriate identification of SI* to SC*.25 Thirdly, the staircase character of SCa* with the third-nearest-neighbour interaction (ANNNI+J3 model)29–34,36 describes well the Devil’s staircase character of described in the following may complicate the situation, particularly when SC* does not emerge.The fourth complexity is the subphases between SCA* and SC*.† rather essential and is due to substrate interfaces which sometimes influence the subphase appearances considerably. Experiment Three antiferroelectric liquid crystal compounds were used in this experiment, the structural formulae of which are summar- † The molecular orientational structures are specified by qT in the onedimensional Ising model with long-range repulsive interactions2 and Scheme 1 A possible, most general subphase sequence in antiferro- by q in the ANNNI+J3 model.29–34 Both of the models assign electric liquid crystals essentially the same structures to SCA* (q=1/2, qT=0), SCc* (q=1/3, qT=1/3), AF (q=1/4, qT=1/2) and SC* (q=0, qT=1) but may predict different ones for subphases in spr3, spr2 and spr1. 407 J.Mater. Chem., 1997, 7(3), 407–416408 ized in Scheme 2. Homogeneously aligned samples were pre- using free-standing films under temperature gradients; an eyepiece together with a beam splitter was added, so that by the pared by rubbing polyimide (Toray, SP510) spin-coated on glass substrate plates with indium tin oxide (ITO) electrodes.use of backward illumination, we can pin-point the sample area where the conoscopic observation occurs. Homeotropically aligned samples were also prepared between glass substrate plates coated with silane coupling agents (Toray Dow Corning Silicone, AY 43-021). Polyester (PET) films were Results used as spacers in both homogeneous and homeotropic cells. Free-standing film samples were formed in a 1.5×8 mm2 12BIMF10 homogeneous cells rectangular hole of a glass frame depicted in Fig. 1. The film Plate 1 shows micrographs of a 6 mm thick 12BIMF10 cell thickness was estimated at ca. 100 mm from the upper and aligned homogeneously by polyimide (Toray, SP510) rubbing. lower film surfaces pinpointed with an optical microscope.An When the phase transition from SA to the unidentified SX1* electric field can be applied parallel to the 1.5 mm edges using phase occurs, needle-like defects emerge perpendicular to the two ITO electrodes prepared along the 8 mm edges. The frame smectic layer, but fringe lines parallel to the smectic layer, has another ITO heater electrode on the right side, which can indicating a helicoidal structure, do not appear; the extinction produce a temperature gradient in the free-standing film directions are parallel and perpendicular to the smectic layer. sample.Samples aligned in a homogeneous/homeotropic cell These are the characteristic features of SCa* and hence SX1* or prepared as a free-standing film were mounted in an oven must be SCa*. On cooling to another unidentified phase SX2*, and the temperature was controlled with an accuracy of both focal conics and fringe lines parallel to the smectic layer, ±10 mK.indicating the helicoidal structure, appear and light trans- Texture observation and electro-optical switching investimission occurs slightly even when the crossed polarizers are gation were performed using the same system as described in set at extinction directions parallel and perpendicular to the previous papers.1,2,22–24 The helicoidal pitch multiplied by the smectic layer; this SX2* texture looks like that of SCc*.As the average refractive index was determined by observing the temperature decreases further, SCA* appears. transmittance loss due to selective reflection using a spectro- The switching currents observed in the same cell at various photometer (Hitachi, U-3410).Laser light diffraction patterns temperatures by applying a 0.5 Hz, ±6 V mm-1 triangular were obtained by the same system as used in photon correlation wave are shown in Fig. 3. In the high-temperature region of spectroscopy with a He–Ne laser and a goniometer.57 Fig. 2 SX1*, two current peaks were observed, suggesting the anti- illustrates a system for obtaining conoscopic figures by applyferroelectric character of SX1*; the number of current peaks ing an electric field to unwind the helicoidal structure.Its increases with the decrease of temperature in SX1*. This details have already been reported in ref. 58, apart from one switching behaviour, together with the texture illustrated in improvement which is essential in the present investigation Plate 1, almost unambiguously identifies SX1* as SCa*. After the phase transition to SX2*, five current peaks were observed; the number of current peaks remains five in SX2*.Since three peaks are expected to appear in SCc*, it is not reasonable to simply identify SX2* as SCc*. Fig. 4 summarizes the laser light diffraction patterns obtained at various temperatures covering SA, SX1*, SX2* and SCA* in a 350 mm thick 12BIMF10 cell aligned homogeneously using a 1 T magnetic field.The phase-transition temperatures are different from those in Fig. 3, because they depend on the cell thickness and surface treatment. In both SA and SX1*, no diffraction peaks emerge and the background lines are sufficiently low and almost noiseless; this was particularly true after all our effort to detect the diffraction peaks in SX1* by changing the temperature at 0.1 °C intervals.When the phase Scheme 2 Compounds used and their phase sequences outlined roughly. Note that substrate interfaces sometimes influence not only transition to SX2* occurs at 54.9 °C, the background lines the transition temperatures but also the phase appearances themselves become very high and noisy and two broad diffraction peaks emerge.The dashed line in Fig. 4 shows the zero level line of the diffraction observed at 54.9 °C. The large-angle diffraction peak moves toward the small-angle side with decreasing temperature, while the small-angle diffraction peak scarcely shows any temperature variation.The two diffraction peaks at the highest temperature in SX2* correspond to periodicities 2.1 and 0.8 mm, which are not in the relation of the first- and second-order diffraction peaks. 12BIMF10 homeotropic cells As described above, at least SX2* appears to be affected Fig. 1 Frame for a free-standing film and holder for producing tem- considerably by substrate interfaces in homogeneous cells.perature gradients Hence we tried to observe the Bragg reflection due to theJ . Mate r . Chem., 1997, 7(3), 407–416 409 Fig. 2 Schematic illustration of the optical system for observing conoscopic figures Plate 1 Micrographs of a 6 mm thick, 12BIMF10 cell homogeneously aligned by polyimide (Toray, SP510) rubbing410 Fig. 4 Laser light diffraction patterns obtained at various temperatures in a 350 mm thick, 12BIMF10 cell aligned homogeneously using a magnetic field.The patterns are shown at 0.1°C intervals and their ordinate zeros are shifted upwards constantly by one division Fig. 3 Switching current observed in the same cell as used in Plate 1 at various temperatures by applying a 0.5 Hz,±6 V mm-1 triangular Fig. 5 Temperature variation (#, cooling; $, heating) of Bragg- wave electric field. The peak indicated by : is due to flow of reflected peaks observed in a 100 mm thick, 12BIMF10 cell homeotrop- accidentally contained ions ically aligned by surfactant (Toray Dow Corning Silicone, AY 43-021) the diffraction peak in Fig. 4 which shifts from 50° to 30° with decreasing temperature. helicoidal structure in a 100 mm thick homeotropic cell.The 12BIMF10 free-standing films results exceeded expectation and a beautiful Bragg reflection was observed; Fig. 5 shows the temperature variation of the In this way, homeotropic cells are much more ideal than homogeneous cells from the viewpoint that some subphase reflected peak. The helicoidal pitch in SCA* must be very short so that the corresponding Bragg reflection could not emerge structures are realized easily.Still, the hysteresis and the disappearance of the red reflection in the low-temperature in the transparent region of 12BIMF10. On heating to SX2*, a red colouration was visible and a Bragg refection peaking at region suggest some influence exerted by substrate interfaces. To be as free from this influence as possible, we observed the ca. 600 nm appeared. On further heating, the peak showed a steep increase to ca. 1.5 mm and then decreased slightly; SX2* subphases in a ca. 100 mm thick free-standing film under a temperature gradient and obtained their conoscopic figures by consists of at least two subphases. After the phase transition from SX2* to SX1*, no Bragg reflection was observed.In a applying an electric field. Plate 2 shows a micrograph under crossed polarizers and two conoscopic figures. Between SCA* cooling process, SX2* behaved similarly in the high-temperature region, but hysteresis was observed and the 600 nm Bragg and SCa*, there exist two ferrielectric phases which must correspond to SX2*. The red Bragg reflection is clearly seen reflection did not appear in the low-temperature region.The 1.5 mm peak nearly corresponds to the periodicity producing and, within this red region, a conoscopic figure illustrated onJ . Mate r . Chem., 1997, 7(3), 407–416 411 we first confirmed SC* by texture observation and then observed a conoscopic figure, which is clearly different from SC* and SCA*; it looks like ferrielectric at 200 V mm-1 but antiferroelectric at 333 V mm-1 as shown in Plate 3.Consequently, we could not identify unequivocally the subphase in spr1 as ferrielectric. Plate 4 shows micrographs and conoscopic figures of ca. 100 mm thick partially racemized TFMHPBC free-standing films. When the optical purity is ee=(R-S)/(R+S)=92%, both SCc* and another ferrielectric subphase in spr3, FIL, were observed clearly between SCA* and SCa* as seen in Plate 4(a).The dark blue colour on the left side is caused by the Bragg reflection due to the SCA* helicoidal structure; the SCA* texture appears very uniform because the helicoidal pitch is short. The dark area on the right side represents SCa*, the texture of which is always quite uniform in homogeneous cells as well as in free-standing films.The difference between the ferrielectric phases becomes much more clear if we observe conoscopic Fig. 6 Apparent tilt angle vs. temperature determined by measuring figures under an applied electric field of 17 V mm-1 as shown centre-shifts in the conoscopic figures under an applied electric field, in Plate 4(a). When the optical purity was slightly reduced to 267 V mm-1 ee=(R-S)/(R+S)=84%, three ferrielectric subphases, FIL in spr3, SCc* and FIH in spr2, and one antiferroelectric subphase, AF, were observed between SCA* and SCa* as seen in Plate 4(b).the lower left is observed when an electric field high enough As demonstrated in this and the preceding sections, free- to unwind the helicoidal structure is applied. The region above standing films under temperature gradients are very effective (to the right of ) the red one becomes dark because of the for the direct observation of the subphases between SCA* and infrared Bragg reflection; a conoscopic figure illustrated on the SC*.When the helicoidal pitch is long, however, the film right in the lower part is observed when unwinding the appearance may become disturbed and spurious phase bound- helicoidal structure.We saw the boundary between this dark aries may appear as illustrated in Plate 5. Even in such cases, region and SCa*, although it is not clear in the plate. conoscopic observation under an applied electric field can We can determine the apparent tilt angle by measuring discriminate between the real and spurious phase boundaries.centre-shifts in the conoscopic figures as plotted in Fig. 6. The Among the several boundaries in the ferrielectric subphases, tilt angle is 21° in SC* produced from SCA* by applying an in fact, the lowest temperature boundary is the real one, electric field stronger than its threshold,and the two ferrielectric because the conoscopic figures observed on both sides of this phases corresponding to the red and dark regionshave apparent boundary are quite different, as shown in Plate 5.tilt angles of 4.2°#21°/5 and 6.9°#21°/3, respectively. Consequently, it is reasonable to assign the two ferrielectric subphases corresponding to SX2*, which exhibit the red and infrared Bragg reflections, as subphases in spr3 and SCc*, Discussion respectively. Note that the Bragg reflection due to the helicoidal The successive phase transitions observed between ferroelectric structure has not been observed in either of the subphases so far.SC* and antiferroelectric SCA* can be regarded as the formation of large-scale structures in simple physical systems other- Free-standing films of TFMHPBC and MHFPDBC wise dominated by short-range forces.Some type of frustration must be present in those parts of the phase diagram where the To recognize properly the validity and limitation of the method using free-standing films under temperature gradients, we structures are encountered. When the two dominant ordering forces of a system happen to compete with each other, a large introduce two other materials, TFMHPBC and MHFPDBC, listed in Scheme 2, although the results obtained are rather number of alternative structures may have almost the same free energy.This degeneracy can be removed either by weak preliminary. The TFMHPBC enantiomer has a simple phase sequence, where only SCa* exists between SCA* and SA, but long-range forces or by thermal effects. The frustration at issue is the one between ferroelectricity and antiferroelectricity, i.e.its racemization complicates the phase sequence.2,10 As far as the authors are aware, MHFPDBC is the only compound in the tilting correlation in adjacent layers, in the SC*-like phase; we would not expect to encounter such frustration, since it which some subphase between AF and SC* has been reported to exist.13 Quite recently, O’Sullivan et al.also reported a seems easy to lift any degeneracy by changing the molecular orientations in some way. In fact, the SC*-like phase has two similar subphase in spr1 in another compound.21 Plate 3 shows a micrograph of a ca. 100 mm thick degrees of freedom, the polar angle, h, and the azimuthal angle, w. Notwithstanding this, several theoretical treatments have MHFPDBC free-standing film under a temperature gradient.We can see clearly the existence of at least one subphase in been developed so far to understand the observed sequence of subphases based on the X–Y model.41–53 spr1. We were unable to observe its conoscope by applying an electric field, because some flow induced by the field occurred Possible antiferroelectric and ferrielectric structures induced by the multilayer tilt ordering from the parent SA have been in SC* on the right side and disturbed the texture considerably.To avoid this flow, we stopped using the temperature gradient constructed systematically on the basis of symmetry analysis. 51,52 To choose realistic structures for the most stable and tried to keep the film temperature uniform. On cooling,412 Plate 2 A micrograph of a ca. 100 mm thick, 12BIMF10 free-standing film under a temperature gradient and two conoscopic figures of a subphase in spr3 (1/2>q>1/3) and SCc* (q=1/3) under an applied electric field, 182 V mm-1, sufficient to unwind the helicoidal structure. The q data presented in this and the following Plates have been determined by comparing the experimental observations with Yamashita’s phase diagram reproduced in Fig. 7. ferrielectric and antiferroelectric subphases, SCc* and AF, we (liquid-crystal-induced circular dichroism) due to the helicoidal structures.60 Consequently, the n-layer (n3) spiral model51,52 naturally have to resort to several experimental facts. The first one is the temperature variation of the smectic layer spacing is not practical for AF, because the apparent n-fold symmetry diminishes biaxiality to such an extent that no optical rotatory observed through the successive phase transitions; the spacing shows only a slight discontinuous change at the transitions, if power could be observed.The bilayer azimuthal mode model for SCc*41,51 is not practical, either, because of the third and any. Moreover, the diffraction peak does not show any change such as splitting.Consequently, the molecular tilt angles are forth experimental facts that the biaxial optical plane orients parallel to the applied field2,61 and that our recent X-ray practically constant, not only in a smectic layer but also from layer to layer; bilayer models with different tilt angles in experiment with synchrotron radiation revealed a Bragg reflection corresponding to three-layer spacing;62 note that the adjacent layers41,44,51 are impractical for SCc*.This fact is in accord with our intuition that smectics are one-dimensional bilayer azimuthal mode model needs to presuppose an azimuthal angle difference of ca.±80° in adjacent layers and is crystal and the layer spacing change accompanies a large energy increase and hence seldom occurs.Empirically, once a unrealistic. Although the low-frequency dielectric properties have been reported to be well understood by the bilayer tilt angle as large as 10° or more has been established, the electroclinic effect59 is hardly observed. azimuthal mode model,47 these characteristic properties can also be explained by the three-layer Ising model.63 The second experimental fact is that AF shows an LCICDJ .Mate r . Chem., 1997, 7(3), 407–416 413 Plate 3 A micrograph of a ca. 100 mm thick, MHFPDBC free-standing film under a temperature gradient, and two conoscopic figures of a ferrielectric subphase in spr1 (1/4>q>0) under 200 and 333 V mm-1; ferrielectric behaviour is shown at 200 V mm-1 and antiferroelectric behaviour is shown at 333 V mm-1 The final experimental fact is well known but is very same as the Ising model which we have already proposed;2,9,65 note that the tilt (polar angle) is practically the same in the important.The helical pitch of antiferroelectric liquid crystals is fairly short compared with conventional ferroelectric liquid three layers (Phase III in Fig. 4) and Phase II in Fig. 3 exists practically even in the chiral case, because the helical structure crystals. However, the chiral interaction is still so weak that the helicoidal pitch is very long as compared to the smectic is only a small perturbation caused by a weak interlayer chiral interaction. layer spacing, i.e. the molecular length.64 Consequently, the subphase sequence analysis based on the Landau-type phenom- What we would like to emphasize is the mechanism by which the tilting direction is restricted parallel to a plane both enological models should be performed carefully by taking account of the short-range interactions to produce large azi- in ferroelectric SC* (w=0) and antiferroelectric SCA* (w=0 or p).As mentioned above, we neglect the slight precession of at muthal angle changes between adjacent layers;44,49,50 the existence of the short-range interaction has not been supported by most a few degrees per layer caused by chirality.The excluded volume effect (the packing entropy effect) in a smectic layer any experimental evidence up until now. In this way, the Ising model appears to be most realistic. It should be noted that structure preserving the density wave character must be the main factor that causes the molecules to tilt in the same Phase II in Fig. 3 of the four-layer model and Phase III in Fig. 4 of the three-layer model in ref. 52 are effectively the direction and sense in SC*. Either of the two models based on414 Plate 4 Micrographs of ca. 100 mm thick, TFMHPBC free-standing films under temperature gradients, and conoscopic figures of a subphase in spr3 (1/2>q>1/3) and SCc* (q=1/3) under applied electric fields, 17 V mm-1; (a) for R5S=9654 and (b) for R5S=9258.A subphase in spr2 (1/3>q>1/4) is also observed on the right side of (b), although no detailed study was performed. the electric interaction between permanent dipole moments peting nearest and next-nearest neighbour coupling proposed by Bak and von Boem.35 proposed so far for the stabilization of SCA*, the pairing model by Takanishi et al.22 and the Px model by Miyachi et al.,66 Trying to simply interpret the observed sequence of the subphases in terms of the Bak–Bruinsma Ising model with the assure that the molecular tilting occurs in the same direction but in the opposite senses in adjacent layers, although the long-range repulsive interactions, we assigned Ising spins to the orderings, ferroelectric (F) and antiferroelectric (A), but third model based on the steric interaction in adjacent layers67 may not be able to do so.In this way, it seems to be not to the tilting senses, right (R) and left (L);2,9,22 we also considered that, following Bruinsma and Prost,28 fluctuations well founded to treat the observed sequence of subphases in terms of the frustration between ferroelectricity and antiferro- of C-directors and hence of spontaneous polarizations cause the long-range repulsive interactions.However, the repulsive electricity based on the Ising model. Statistical mechanics models illustrating two different ways of lifting the degeneracy interactions between separate F orderings seem to be rather artificial and several difficulties have been noted so far.2 In have been developed: the one by weak long-range forces is the one-dimensional Ising model proposed by Bak and fact, Bruinsma and Prost,28 based on the fluctuation forces, actually showed the emergence of the electric-field-induced Bruinsma26,27 and the other by thermal effects is the so-called ANNNI (axial next-nearest neighbour Ising) model with com- Devil’s staircase which can be described by the tilting senses,J .Mate r . Chem., 1997, 7(3), 407–416 415 Plate 4 (continued) R and L , but not that of the temperature-induced one. for the first, second and third neighbouring pairs in the axial direction parallel to the layer normal; the second-nearest Moreover, the stability of subphases changes critically from material to material, although the Bak–Bruinsma Ising model neighbour interaction J2 should be negative to ensure competition, and the third-nearest neighbour interaction J3 (>0 or predicts rather universal stability.26,27 Another issue raised is that no finite temperature effect is taken into account and <0) is included for the possible wide stability of SCc*. Although they did not show any realistic physical grounds for hence the model can describe only the ground states.50 The ANNNI+J3 model36 was applied to this problem by these rather long-range interactions initially, Yamashita32–34 quite recently claimed an important role played by the sense Yamashita and Miyazima29 and by Yamashita.30,31 The Hamiltonian they assumed is of the molecular long axis, decimated in the partition function the pseudo-spins describing the senses of molecular long axes, and eventually obtained the effective long-range interactions, H=-J .(i,j) sisj-J1 .i A sisi+1-J2 .i A sisi+2-J3 .i A sisi+3 J2, J3 , etc. Such a freedom was already introduced by Koda and where the Ising spin si takes a value of ±1 corresponding to Kimura37,38 to induce negative J2, who also quite recently the molecular tilting senses of the ith smectic layer, the first extended their theoretical treatment and tried to interpret the summation is taken all over nearest-neighbouring pairs (i, j) in the same smectic layer, and other summations SA are only observedsequence of subphasesand the stabilityranges.39 Their416 Plate 5 A micrograph of a TFMHPBC (R5S=88512) free-standing film under a temperature gradient, and two conoscopic figures of a subphase in spr3 (1/2>q>1/3) and SCc* (q=1/3), respectively. Some spurious phase boundaries appear; the boundary characterizing a phase in spr2 (1/3>q>1/4) on the right side seems to be real, although a conoscopic study was not performed.method is essentially equivalent to the ANNNI+J3 model. to be very small for q=2/9 and 1/5, and this smallness may explain the characteristic field dependence of the conoscopic Yamashita34 showed that four ground states are SCA* (q=1/2), SCc* (q=1/3), AF (q=1/4) and SC* (q=0) as illustrated in figure for the subphase in spr1 observed in Plate 3.It exhibits ferrielectric-like behaviour at low fields, but a secondary inter- Fig. 7. He predicted rather stable ferrielectric phases q=2/5 and 4/11 in spr3, q=4/13 and 2/7 in spr2, and q=2/9 and 1/5 in action through dielectric anisotropy prevails at high fields, resulting in the antiferroelectric conoscopic figure. Yamashita spr1, estimating the average of the saturated ordering, also predicted antiferroelectric phases, q=3/8, q=3/10 and q= s=.p i=1 si p 3/14, in spr3, spr2 and spr1, respectively.which is considered to be proportional to the apparent tilt Conclusions angle, i.e. the spontaneous polarization. The estimated ratio of this value to that in SCc* (q=1/3) is ca. 0.6 for q=2/5 and ca. In this way, the ANNNI+J3 model,29–34,36 is flexible enough to explain a variety of observed phase sequences between SCA* 0.27 for q=4/11.The subphase in spr3 observed in Plate 2 and Fig. 6 is therefore identified as q=2/5. The ratio is suggested and SC*. For detailed comparison of theory with experiment,J . Mate r . Chem., 1997, 7(3), 407–416 417 13 H. Hatano, Y. Hanakai, H. Furue, H. Uehara, S.Saito and K. Muraoka, Jpn. J. Appl. Phys., 1994, 33, 5498. 14 H. Moritake, N. Shigeno, M. Ozaki and K. Yoshino, L iq. Cryst., 1993, 14, 1283. 15 H. Moritake, M. Ozaki, H. Taniguchi, K. Satoh and K. Yoshino, Jpn. J. Appl. Phys., 1994, 33, 5503. 16 P. Gisse, J. Pavel, H. T. Nguyen and V. L. Lorman, Ferroelectrics, 1993, 147, 27. 17 P. Cluzeau, H. T. Nguyen, Ch. Destrade, N.Isaert, P. Barois and A. Babeau, Mol. Cryst. L iq. Cryst., 1995, 260, 69. 18 M. Glogarova, H. Svorenyak, H. T. Nguen and Ch. Destrade, Ferroelectrics, 1993, 147, 37. 19 T. Sako, Y. Kimura, R. Hayakawa, N. Okabe and Y. Suzuki, Jpn. J. Appl. Phys., 1996, 35, L114. 20 Yu. P. Panarin, H. Xu, S. T. MacLughadha, J. K. Vij, A. J. Seed, M. Hird and J. W. Goodby, J. Phys.: Condens. Matter, 1995, 7, L351. 21 J.W. O’Sullivan, Yu. P. Panarin and J. K. Vij, Poster Presentation at 16th Int. L iq. Cryst. Conf. (Kent, 1996), C1P.15 (P-125). 22 Y. Takanishi, K. Hiraoka, V. K. Agrawal, H. Takezoe, A. Fukuda and M. Matsushita, Jpn. J. Appl. Phys., 1991, 30, 2023. Fig. 7 A phase diagram obtained by the ANNNI+J3 model for 23 K. Hiraoka, Y. Takanishi, K. Skarp, H. Takezoe and A.Fukuda, J1/|J2|=1 and J3/|J2|=0.3. By courtesy of M. Yamashita.29–34 Jpn. J. Appl. Phys., 1991, 30, L1819. 24 T. Isozaki, K. Hiraoka, Y. Takanishi, H. Takezoe, A. Fukuda, Y. Suzuki and I. Kawamura, L iq. Cryst., 1992, 12, 59. a much more systematic determination of the apparent tilt 25 M. Neundorf, Y. Takanishi, A. Fukuda, S. Saito, K. Murashiro, angle and helicoidal pitch in spr3, spr2, and spr1 needs to be T.Inukai and D. Demus, J.Mater. Chem., 1995, 5, 2221. performed with improved accuracy using free-standing films. 26 P. Bak and R. Bruinsma, Phys. Rev. L ett., 1982, 49, 249. 27 R. Bruinsma and P. Bak, Phys. Rev. B., 1983, 27, 5824. Some refinement is also necessary in the theoretical treatment. 28 R. Bruinsma and J. Prost, J. Phys. II (France), 1994, 4, 1209.Although Koda and Kimura39 considered that the polar angle 29 M. Yamashita and S. Miyazima, Ferroelectrics, 1993, 148, 1. is fluctuating, the azimuthal angle is much more liable to 30 M. Yamashita, Mol. Cryst. L iq. Cryst., 1995, 263, 93. fluctuate and has the first claim to consideration; the tilt angle 31 M. Yamashita, Ferroelectrics, 1996, 181, 201. decrease toward SA should also be taken into account. These 32 M.Yamashita, J. Phys. Soc. Jpn., 1996, 65, 2122. refinements may allow us to understand not only the variety 33 M. Yamashita, J. Phys. Soc. Jpn., 1996, 65, 2904. 34 M. Yamashita, Poster Presentation at 16th Int. L iq. Cryst. Conf. of observed phase sequences between SCA* and SC* but also (Kent, 1996), C1P.12 (P-124), Mol. Cryst.L iq. Cryst., to be SCa*2,22–24 and the V-shaped switching due to thresholdless published. antiferroelectricity disclosed recently.68–71 35 P. Bak and J. von Boem, Phys. Rev. B, 1980, 21, 5297. 36 Y. Yamada and N. Hayama, J. Phys. Soc. Jpn., 1983, 52, 3466. We are grateful to Mamoru Yamashita, Kou Tokumaru and 37 T. Koda and H. Kimura, Ferroelectrics, 1993, 148, 31. Sauseong Seomun for stimulating discussions and for allowing 38 T.Koda and H. Kimura, J. Phys. Soc. Jpn., 1995, 64, 3787. 39 T. Koda and H. Kimura, J. Phys. Soc. Jpn., 1996, 65, in press. us to use Fig. 7. This work was supported by a Grant-in-Aid 40 M. Nakagawa, J. Phys. Soc. Jpn., 1993, 62, 2260. for Scientific Research (Specially Promoted Research 41 H. Orihara and Y. Ishibashi, Jpn. J. Appl.Phys., 1990, 29, L115. No. 06102005) from Monbusho in Japan. 42 H. Orihara and Y. Ishibashi, Jpn. J. Appl. Phys., 1990, 30, L1819. 43 H. Sun, H. Orihara and Y. Ishibashi, J. Phys. Soc. Jpn., 1991, 60, 4175. References 44 H. Sun, H. Orihara and Y. Ishibashi, J. Phys. Soc. Jpn., 1993, 62, 2706. 1 A. D. L. Chandani, E. Gorecka, Y. Ouchi, H. Takezoe and A. Fukuda, Jpn. J. Appl. Phys., 1989, 28, L1265. 45 B. Zeks, R. Blinc and M. Cepic, Ferroelectrics, 1991, 122, 221. 46 B. Zeks and M. Cepic, L iq. Cryst., 1993, 14, 445. 2 A. Fukuda, Y. Takanishi, T. Isozaki, K. Ishikawa and H. Takezoe, J.Mater. Chem., 1994, 4, 997. 47 M. Cepic, G. Heppke, J-M. Hollidt, D. Lotzsch and B. 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Nagata and Y. Mori, SID ’96 Digest [Ext. Abstr. Int. Symposium, Seminar, & Exhibition (San Ferroelectrics, 1993, 147, 147. 64 J. Li, H. Takezoe and A. Fukuda, Jpn. J. Appl. Phys., 1991, 30, 532. Diego, 1996)], 28.4. 65 H. Takezoe, J. Lee, Y. Ouchi and A. Fukuda, Mol. Cryst. L iq. Cryst., 1991, 202, 85. 66 K. Miyachi, J. Matsushima, Y. Takanishi, K. Ishikawa, H. Takezoe Paper 6/05942B; Received 28th August, 1996 and A. Fukuda, Phys. Rev. E, 1995, 52, R2153.

ISSN:0959-9428    

DOI:10.1039/a605942b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Polarised photoluminescence from oriented polymer liquid crystal films Andrew P. Davey,* Robert G. Howard andWerner J. Blau Department of Physics, University of Dublin, T rinity College, Dublin 2, Republic of Ireland Optical anisotropy in a new form of crosslinked liquid crystal network incorporating a fluorescent chromophore has been demonstrated. Linearly polarised absorption and fluorescence is observed in oriented thin films.From measurement of absorption and fluorescence anisotropy, the order parameter was found to be 0.65 and 0.80, respectively. Temperature dependent birefringence measurements reveal that there is no appreciable loss of alignment up to 200 °C. The last few years has seen many advances in the field of would preferentially emit light in a particular polarisation and would exhibit good thermal stability properties.We therefore organic optoelectronics, specifically, light emitting devices using polymers and other smaller molecules.1 The performance set out to design and synthesise a liquid crystal with an emissive functional core and crosslinkable side-groups. Our of such devices has improved considerably due to optimisation of material interfaces, improvement of quantum yield and a aim was to utilise such a liquid crystal in an ordered thin film form.better understanding of charge transport processes in amorphous organic systems. The point has now been reached where more sophisticated devices, such as organic microcavity struc- Synthesis and characterisation tures2 and polarised emitters,3 are beginning to be reported. In any study of new systems, the starting point is characteris- In order to produce oriented films with linearly polarised ation of the optical (absorption and photoluminescent) proper- emission characteristics, a chromophore with a blue–violet ties.This paper therefore presents the optical characterisation emissive core and acrylate functionalities (3) was synthesised.of a new method of inducing polarised photoluminescence by The synthetic route to 3 is depicted in Scheme 1. A similar the use of aligned, crosslinked liquid crystal networks. molecule without any functionalities at the end of the alkyl To date, work in this area has employed a number of tails has been previously synthesised8 and the same general different alignment techniques designed to induce polarised method was used to prepare 2.Compound 3 was character- emission. The first technique is controlled chemical vapour ised by IR, 1H NMR, 13C DEPT NMR and UV–visible deposition (CVD) which has been used to produce polycrystal- spectroscopy. line thin films of small conjugated organic molecules.4 The Differential scanning calorimetry (DSC) showed that 3 exhi- second technique is Langmuir–Blodgett film deposition, which bits a small enthalpy phase transition at 36°C and a larger was used to fabricate polarised polymer light emitting diodes.5 transition (to the isotropic phase) at 80°C on the heating cycle.Finally, polarised luminescent films have been produced from On the cooling cycle, however, no phase transitions could be functionalised polymer liquid crystals by substrate rubbing- observed.This is possibly due to slow recrystallisation, since induced alignment in the liquid crystal phase.6 on cooling overnight the phase transitions had returned. These techniques have been applied with varying degrees of Compound 3 exhibits strong blue–violet fluorescence in success; there are still some problems to overcome.All of the dilute chloroform solutions. Fig. 2 shows the electronic absorp- techniques have so far failed to produce particularly high tion and fluorescence spectra of the compound in dilute toluene degrees of linear polarisation. The approach which we have solution. The quantum yield of fluorescence in chloroform was used in an attempt to overcome some of these problems is in determined by a comparative method9 and was found to be situ photopolymerisation of functionalised oriented liquid crys- 60% in dilute solutions of cyclohexane.tals to produce highly aligned chromophore networks. This technique has been studied for a number of years7 for potential application in solid state liquid crystal display devices. Its exploitation in other areas is still, however, limited.To produce these oriented polymer networks, in situ photopolymerisation of macroscopically oriented mixtures of liquid crystal (LC) diacrylates was used. Fig. 1 depicts the photopolymerisation process in the liquid crystal phase. This technique involves the macroscopic alignment of the LC diacrylates and the ‘freezing-in’ of the orientation by photo-polymerisation.Previous work has invariably employed molecules where the saturated carbon chains are positioned at either end of the long axis of the liquid crystal core.7 In our case however, the alkyl chains are bonded across the short axis of the core (see Fig. 1). Networks obtained by this method are highly crosslinked and well ordered. This high degree of orientation is both thermally and temporally stable.Results and Discussion In this study, we sought to utilise the long range ordering Fig. 1 Schematic of in situ photopolymerisation characteristics of liquid crystals to produce a thin film which J. Mater. Chem., 1997, 7(3), 417–420 417Fig. 3 Linear polarisation dependence of optical absorption (a) parallel and (b) perpendicular to the director through cross-polarisers under a microscope.Unfortunately, no long-range ordering was observed in this intermediate phase. In order to produce a low viscosity nematic phase, 5% by weight of 3 was mixed with 1,4-phenylenebis{4-[6-(acryloyloxy) hexyloxy]benzoate}, a previously studied crosslinkable nematic liquid crystal.10 The same proportion of photoinitiator and thermal inhibitor as before was then added.This new mixture exhibited a crystalline–nematic phase transition at 116°C and a nematic–isotropic transition at 150°C. Glass cells Scheme 1 Reagents and conditions: i,HO(CH2)6Br (2 equiv.), butanone, K2CO3, heat; ii, PhCOCH (2 equiv.), piperidine, Pd(PPh3 )4, CuI, containing this mixture were found to exhibit long range 90 °C, 36 h; iii, CH2NCMeCOCl (2 equiv.), CH2Cl2, Et3N ordering in the nematic phase.It was possible to ‘freeze-in’ this long range ordering by photopolymerisation. This procedure was found to be effective for loadings of up to 15% by weight of 3. Polarised absorption and emission studies In order to measure optical anisotropy in the film, polarisation dependent UV–visible absorption spectra were recorded.Spectra recorded for polarisations perpendicular and parallel to the director and normalised for the polariser absorption are shown in Fig. 3. Clearly, the oscillator strength in absorption is concentrated along the direction of rubbing. The order parameter S was calculated by comparing peak absorption (355 nm) parallel and perpendicular to the direction of rubbing, according to eqn.(1), S= APA-APE APA+2APE (1) where APA and APE are the values of absorbance parallel and perpendicular to rubbing respectively. The value of S for Fig. 2 (a) Absorption and (b) fluorescence spectra of a toluene solution absorption was thus found to be 0.65, which compares favour- of 3 ably with values found for similar non-fluorescent systems.10 It is noteworthy that there appears to be an extra absorption Phase transition studies band in the perpendicular absorption spectrum.The origin of The phase transitions of compound 3 were studied using DSC this band is not clear, it may perhaps be a weak vibrational and polarising microscopy. The material is crystalline at room mode (bending mode) polarised primarily across the long axis temperature and on heating shows a phase transition at 36°C of the fluorescent molecule.Whatever the origin of the band, to an unidentified intermediate phase. The transition from this its presence reduces the value of S as determined by absorption. intermediate phase to the isotropicphase has an onset tempera- The emission spectra (for an excitation wavelength of 350 nm) ture of 69°C and the peak is at 80°C.The sample exhibits no parallel and perpendicular to the rubbing direction are shown phase transitions when it is cooled from the isotropic phase in Fig. 4. There is obviously a strong linear polarisation of the until below 30°C, where it crystallises. blue–violet emission. By way of comparison, the order parameter was again determined by comparing the numerically Long range ordering integrated emission spectra for the parallel and perpendicular directions according to eqn.(2), a modified form of eqn. (1), A mixture of 3, photoinitiator (2 mol%; CIBA-Irgacure@ 651) and thermal inhibitor (4-methoxyphenol; 0.1 mol%) was prepared. A glass cell was filled with the mixture in molten form by capillary action, and the sample was cooled overnight to S= P2 0 EPA dl-P2 0 EPE dl P2 0 EPA dl+2AP2 0 EPE dlB (2) allow recrystallisation. The sample was heated to its intermediate state (50°C) and any ordering in the film was observed 418 J.Mater. Chem., 1997, 7(3), 417–420Thin film preparation Oriented photopolymerised thin films were produced by an oriented rubbing method. A liquid crystal display type glass cell of 10 mm thickness was fabricated.The inside walls of the cell were coated with a thin layer (ca. 0.1 mm) of spun cast Nylon 66 which was rubbed along one direction of the film plane in order to induce alignment when the glass cell was filled with liquid crystal material. Long range ordering could not be induced in samples of compound 3. Thus ordered thin films of 3 could not be produced. Compound 3 (5% by weight) was mixed with 1,4-phenylenebis{ 4-[6-(acryloyloxy)hexyloxy]benzoate}. Photoinitiator (2 mol%; CIBA-Irgacure@ 651) and thermal inhibitor (4-methoxyphenol; 0.1 mol%) was added.A glass cell containing the Fig. 4 Linear polarisation dependence of photoluminescence (a) par- mixture was brought to 130°C (nematic phase) and photopo- allel and (b) perpendicular to the rubbing direction lymerised by irradiation for 20 min with a low intensity UV fluorescent lamp (4W).The crosslinked film thus produced where EPA and EPE are the emission intensities parallel and was of very good optical quality and exhibited no sign of perpendicular to orientation respectively. phase separation or photodegradation. The same film was In this case, S was found to 0.80, a relatively high value.used in all subsequent studies. The discrepancy between S determined by absorption and S found by emission probably arises either from the different Absorption and fluorescence measurements measurement geometry or from the presence of the extra band in the perpendicular absorption. In the case of absorption Polarised absorption spectra were obtained using an ATI transmitted light is monitored, whereas for fluorescence it is UV–visible absorption spectrometer and a Rowi 55 mm polar- light scattered from the sample surface which is detected.iser. The polariser was placed between the spectrometer source and the film sample. The parallel absorption spectrum was Variation of order with temperature recorded with the direction of polarisation parallel to the rubbing direction of the film.The polariser was rotated 90° In order to monitor changes in order as a function of heating, and the perpendicular absorption spectra was recorded. temperature dependent birefringence was measured using a Polarised fluorescence spectra were measured using a Perkin hot stage and a polarising microscope (equipped with a Leitz Elmer MPF-4413 spectrophotometer. The spectrophotometer typeM tilting compensator).This method was specifically used source was intrinsically polarised so no polariser was required. since thermal processes might affect the temperature dependent The parallel and perpendicular spectra were recorded by emission characteristics independent of order. Fig. 5 shows the aligning the film at the appropriate angle (0 or 90°) with variation of birefringence with temperature.There is little or respect to the polarised source. The film was placed at an no change in order as temperature increases. This is due to angle of 45° to both the excitation source and detector. The the very rigid nature of the crosslinked liquid crystal network. excitation wavelength was 350 nm.Similar characteristics to this have been observed for other acrylate functionalised liquid crystal networks.11 It is also interesting to note that the birefringence returns Birefringence measurements to its original value on cooling to ambient temperature, indicating that fluctuation of order is probably due to random Measurements were performed using a Leitz polarising microthermal motion rather than relaxation of the order.scope and a Leitz tilting compensator (type M at 546 nm). The samples were heated using a microscope hot stage and a Eurotherm temperature controller. Experimental Differential scanning calorimetry (DSC) measurements Preparation of the fluorescent compound Measurements were performed on a Perkin Elmer DSC-4. The All reactions were performed under an argon atmosphere.All sample quantities were in the range of 10 mg. The heating and solvents were dried and degassed before use. Reagents were cooling rates were 10°C per minute, the measurements were used as supplied from the Aldrich Chemical Company. NMR carried out under an inert nitrogen atmosphere. spectra were recorded in CDCl3 solution with an internal Me4Si standard.Synthesis of compound 2. Compound 1 (1 mmol) and phenylacetylene (2.1 mmol) were dissolved in 30 ml of piperidine. Pd(PPh3)4 (0.046 g, 2 mol%) and copper(I) iodide (4 mg) were then added and the mixture was stirred at 90°C for 6 h. Following cooling, the precipitated hydrobromide salts were filtered and washed with hexane. The washings were combined with the piperidine solution and the solvents were removed under vacuum.The resulting solid was recrystallised from butanone (0.42 g, 83%); 1H NMR: d 0.92–1.80 [m, 8H, (CH2)4], 3.78 (t, 2H, OCH2 ), 3.83 (t, 2H, HOCH2), 6.81 (s, 1H, Ar-H), 7.20–7.60 (m, 5H, Ar-H); 13C NMR: d 22.5, 25.4, 29.8 and 32.0 (CH2), 69.9 (OCH2), 72.4 (HOCH2), 86.3 and 95.0 (sp-C), 114.2 (Ar-C), 117.1 (Ar-C), 123.4 (Ar-C), 128.1 (Ar-C), Fig. 5 Temperature dependence of birefringence: (#) heating and (+) cooling 132.0 (Ar-C) and 154.0 (Ar-C). J. Mater. Chem., 1997, 7(3), 417–420 419Synthesis of compound 3. Compound 2 (0.5 mmol) was absorptionspectrum. Further studies on fabrication and testing of electrically driven devices are in progress with a view to dissolved in 20 ml of THF along with hydroquinone stabiliser (3 mg) and triethylamine (1.1 mmol).The solution was heated producing highly polarised light emitting diodes. to reflux and methacryloyl chloride (1.1 mmol) dissolved in This work was carried out under the EU ESPRIT programme 5 ml of CH2Cl2 was gradually added. Stirring was continued (LUPO project). The authors would like to thank F. M. Coyle for 2 h before the solution was allowed to cool to room for help with DSC measurements.temperature. The mixture was then poured into 150 ml of water and washed with saturated sodium carbonate(3×20 ml), dried and the solvent evaporated in vacuo. The solid was References recrystallised from ethanol (0.23 g, 60%); 1H NMR: d 1 J. H. Burroughs, D. D. C. Bradley, A. R. Brown, R. N. Marks, 1.52–1.85(m, 8H), 4.00(t, 2H), 4.18(t, 2H), 5.02(s, 3H), 5.81(d, K.Mackay, R. H. Friend, P. L. Burns and A. B. Holmes, Nature, 1H), 6.13(d, 1H), 6.80(s, 1H), 7.21–7.62(m, 5H); 13C DEPT 1990, 347, 539. NMR: d 25.71 (CH2), 28.53(CH2) 29.07(CH2), 64.48(CH2), 2 A. Ochse, U. Lemmer, M. Deussen, J. Feldman, A. Greiner, 67.95(CH2 ), 86.20(COC), 94.87(COC), 101.20(CH3), R. F. Mahrt, H. Ba�ssler and E.O. Gobel, Mol. Cryst. L iq. Cryst., 114.12(Ar-C), 117.24(Ar-CH), 124.16(Ar-CH), 128.32(Ar-CH), 1994, 256, 335. 3 S. Chen, Proceedings of the NEDO Workshop on Organic 131.24(Ar-CH), 146.59(CH), 147.20(CH2), 153.98(ArC–O), Microcavities, 1996. 159.92(CNO). 4 R. Marks, Proceedings of the NEDO Workshop on Organic Microcavities, 1996. 5 V. Cimrova�, M. Remmers, D. Neher and G. Wegner, Adv.Mater., Conclusion in the press. 6 G.Lu� ssem, R. Festag, A. Greiner, C. Schmidt, C. Unterlechner, Thin films of a new orienrosslinked liquid crystal mixture W. Heitz, J. H. Wendorff, M. Hopmeier and J. Feldmann, Adv. have been shown to exhibit strongly polarised absorption and Mater., 1995, 7, 923. emission and large order parameter values. Furthermore, 7 D. J. Broer, H. Finkelmann and H. Kondo, Makromol. Chem., temperature dependent birefringence measurements indicate 1988, 189, 185. that order in the sample is largely maintained at elevated 8 R. Giesa, Ph.D. thesis, University of Meinz, 1989. 9 A. P. Davey, S. Elliott, O. O’Connor and W. Blau, J. Chem. temperatures. Commun., 1995, 1433. It was also noted that the birefringence (and hence order) 10 D. J. Broer, J. Boven, G. N. Mol and G. Challa,Makromol. Chem., returned to its original value on complete cooling. 1989, 190, 2255. Measurement of the order parameter from absorption and 11 D. J. Broer, R. A. M. Hikmet and G. Challa, Makromol. Chem., emission provides large values. The discrepancy between these 1989, 190, 3202. values is probably due to different measurement techniques or to the extra absorption feature in the perpendicular polarised Paper 6/05405F; Received 2nd August, 1996 420 J. Mater. Chem., 1997, 7(3), 417–420

ISSN:0959-9428    

DOI:10.1039/a605405f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Radiation chemistry and the lithographic performance of chemical amplification resists formulated from poly(4-epoxystyrene-stat-styrene) and a photoacid generator Richard G. Jones,* Gerard P-G. Cordina and Julian J. Murphy Centre forMaterials Research, Department of Chemistry, University of Kent, Canterbury, Kent, UK CT2 7NH Copolymers of styrene and 4-epoxystyrene in formulations with triphenylsulfonium hexafluoroantimonate as a photoacid generator undergo a crosslinking reaction by a chain mechanism when irradiated with 20 keV electrons and hence act as negativeworking electron-beam resists.The copolymers have been prepared by a free radical mechanism over the entire composition range and the lithographic performance of the materials has been evaluated. The sensitivities of the resist formulations are shown to correlate with the epoxystyrene content of the copolymers in accordance with a simple model of the radiation chemistry of the system.Contrast variations are explained in terms of the statistical structure of the copolymer and it is demonstrated that at low epoxystyrene contents the systems behave in accordance with an unsensitised single-stage crosslinking mechanism.The copolymers with epoxystyrene contents greater than ca. 8% have such high lithographic sensitivities and show such a good tolerance of processing variations as to commend the optimisation of their performance with a view to their subsequent application as electron-beam resists. The use of so-called chemical amplification resists is becoming with good resistance to oxygen plasma, and excellent tolerance to process variation.The measured contrasts for these systems more commonplace in microlithography as their enhanced response, achieved through some radiation-induced chain tend to be low but this has little effect upon the resolution that can be attained, as features with dimensions as low as mechanism, leads to the sensitivity necessary for the economic exploitation of many modern writing tools.However, many of 0.1 mm have been demonstrated.12 One drawback of the Hatzakis systems is that it is not those presently available are multicomponent systems which have little tolerance of process variations. Typically, even a possible to prepare a range of polymers with structures sufficiently controlled as to allow a structure process optimisation.very small change in the post exposure bake (PEB) temperature or time, required to realise the chemical amplification, might Novalac resins are not amenable to molecular mass control and the extent of their subsequent epoxidation cannot be drastically alter the performance of the resist.1 Some systems are also sensitive to environmental contaminants such as controlled. Here we report the microlithographic performance of electron-beam resist formulations based on a series of airborne amines.2 Such problems make for great difficulty in achieving reproducibility.Positive-working systems commonly poly(4-ethenylphenyloxirane-stat-styrene) copolymers. These can be viewed as epoxy novalac analogues, but their synthesis depend on the deprotection of a functional group by radiationgenerated acid or base, which renders the exposed regions of by radical polymerisation allows polymers of controlled molecular mass and epoxy content to be produced.the resist soluble in an aqueous-based development process. Negative-working systems usually rely on a chain crosslinking process which again is most commonly initiated by acid or base formed during exposure.Thus, two components, a polymer and a photoacid generator (PAG) such as an onium salt, are the minimum required in such formulations but it is by keeping to this minimum that processing difficulties can be contained. Amongst the useful functional groups that might be employed in negative-working systems is the oxirane group.This group, which can undergo a radiation-induced chain crosslinking reaction, confers a high sensitivity upon polymeric resists that contain it. Oxirane functionalised polymers such as epoxidised poly(butadiene) or poly(isoprene)3 and poly(glycidyl methacrylate)4,5 were first investigated as electron-beam resists over twenty years ago. Unfortunately, the poor thermal stability of these aliphatic materials at the temperatures commonly encountered in lithographic processing has limited their exploitation.In terms of processibility, even the GMC series of resists (copolymers of glycidyl methacrylate and 3-chlorostyrene) with their considerable aromatic content fall far short of other copolymer resists based on poly(styrene) structures.6–9 More recently, Hatzakis et al.have reported the lithographic performance of epoxy novalac resins in formulations with triphenylsulfonium hexafluoroantimonate as a PAG, as photo-, electron-beam and X-ray resists10,11 as depicted in Scheme 1. Being aromatic materials, these display a number of the desirable properties associated with poly(styrene)-based resists Scheme 1 such as excellent film forming ability, thermal stability allied J.Mater. Chem., 1997, 7(3), 421–427 421DSC-7 differential scanning calorimeter operating at a scan rate of 10°C min-1. Resist solutions were formulated by dissolving the polymers in propylene glycol methyl ether acetate to produce 15% solutions. Unless otherwise stated, the PAG, triphenylsulfonium hexafluoroantimonate, was also dissolved to 4%.The resist solutions were filtered through 0.5 mm Millipore filters and spun directly onto 3 inch† silicon wafers using a Headway EC-101 spinner to produce films of thickness in the range 0.5 mm. Lithographic assessment was accomplished using a CambridgeInstruments EBMF10.5 electron-beam lithography tool operating at a 20 kV accelerating potential. After exposure the wafers were cut into segments which were then either developed immediately, or baked in an oven for 3 min at 90°C prior to development.For process latitude studies, the postexposure bake (PEB) times and temperatures were increased to up to 9 min and 150 °C respectively. Pattern development was accomplished by immersing the wafer segments in methyl isobutyl ketone (MIBK) for 60 s, rinsing in isopropyl alcohol‡ and drying in a stream of nitrogen.Film thickness measurements before and after exposure were measured using a Nanospec/AFT 210 Film Thickness System. All thicknesses were normalised to the original spun thickness. Sensitivities were estimated both as the gel dose (D0) and as the dose corresponding to 50% thickness remaining after development Scheme 2 (D0.5).Lithographic contrasts, c, were calculated from D0.5 and D0 using eqn. (1). Experimental c=1/[2log(D0.5/D0)] (1) Materials Conversion of the incident radiation dose in mC cm-2 to absorbed radiation dose in Mrad was carried out in accordance Styrene (S) was supplied by Aldrich Chemical Co. Ltd. and with the method developed by Novembre and Bowmer.15 For distilled under reduced pressure at 40–50 °C prior to use. 4- a resist film having an approximate thickness of 0.5 mm and a Ethenylphenyloxirane (4-epoxystyrene, ES) was prepared in density of 1 g cm-3, it can be shown that a conversion factor accordance with the method of Truxa and Suchopa�rek13 shown of about 2 Mrad per (mC cm-2) for 20 keV electrons applies. in Scheme 2, and distilled under reduced pressure (65°C at This is the value that has been used in this study. 0.1 mmHg) from sodium hydroxide prior to use. Copolymerisations initiated by 2,2¾-azoisobutyronitrile were carried out in toluene solution inside stoppered boiling tubes Results at 70°C, under dry argon. The polymers were precipitated in The effect of copolymer composition a large excess of chilled methanol, reprecipitated from toluene solution, filtered and dried under vacuum.Precise experimental All of the 4-epoxystyrene/styrene copolymers have glass trans- details of similar copolymer preparations have been reported ition temperatures that are sufficiently high to meet the elsewhere.14 demands of lithographic processing. These, together with the structural and lithographic parameters of a series of resists Apparatus and procedures formulated from the copolymers and triphenyllfonium hexa- flouroantimonate, are recorded in Table 1.Representative con- Copolymer compositions were established from integration of trast curves are depicted in Fig. 1. With the exception of P1, 270 MHz 1H NMR spectra obtained at room temperature, in the number average molecular masses (M� n) of the copolymers CDCl3 solution, using a JEOL JNM-GX270 spectrometer.were controlled at about 15000. The asymptotic departure of Chemical shifts are relative to SiMe4 . Molecular masses and polydispersities were determined as linear polystyrene equivalents using HPLC equipment supplied † 1 in=2.54 cm. by Polymer Laboratories Ltd. and equipped with a mixed-bed ‡ The solvent development system and development times have not 5 mm PLgel column.Glass transition temperatures were deter- been optimised and were chosen simply because they are regularly used with negative-working resists based on poly(styrene) derivatives. mined under a nitrogen atmosphere using a Perkin-Elmer Table 1 Structural parameters and lithographic properties of 4-ES/S copolymer resists in formulations containing 4% triphenylsulfonium hexafluoroantimonate baked resists unbaked resists 4-ES polymer (%) M2 Ma PD Tg/°C D0.5 D0 c Gn D0.5 D0 c Gn P1 100 15 500 9700 1.56 140 0.190 0.045 0.80 160 0.263 0.051 0.70 110 P2 30 30 400 17000 1.79 118 0.70 0.18 0.85 33 0.77 0.18 0.85 28 P3 18 28 000 15100 1.85 113 1.14 0.35 0.97 24 1.45 0.41 0.91 19.3 P4 12 25 800 14500 1.76 104 2.55 1.00 1.23 9.1 4.51 1.30 0.92 9.1 P5 10 28 400 16300 1.75 104 3.84 1.27 1.0 7.3 7.93 2.67 1.1 5.7 P6 8 26 100 14100 1.83 97 6.3 2.5 1.2 3.9 14.0 7.5 1.8 3.1 P7 4 25 100 14500 1.72 93 56.5 33.5 2.2 1.0 65.5 41.0 2.5 1.0 P8 2 24 700 14400 1.71 93 94.3 66.5 3.3 0.9 99.6 72.4 3.6 0.9 422 J.Mater. Chem., 1997, 7(3), 421–427Table 2 The lithographic properties of 4-ES/S copolymer P6 in resist formulations over a range of triphenylsulphonium hexafluoroantimonate loadings baked resists unbaked resists %PAG D0.5 D0 c D0.5 D0 c 0 — — — 37.9 23.1 2.30 0.25 17.1 3.3 0.70 23.5 10.5 1.43 0.5 14.8 3.6 0.81 22.4 10.6 1.54 1.0 10.1 2.6 0.85 21.6 11.0 1.71 2.0 7.6 2.0 0.86 21.5 10.6 1.63 4.0 6.3 2.5 1.25 14.0 7.5 1.84 Fig. 2 Variation of lithographic sensitivity with copolymer composition for the single-stage crosslinking resists.The progressive inclusion of up to 30% epoxystyrene in this copolymer causes the contrast to drop to 0.85 from an initial value of 3.6 for the homopolymer, polystyrene. The contrast of the corresponding chlorostyrene/methylstyrene system of comparable molecular mass, over the same composition range, holds at ca. 2.5.The effect of post exposure bake From Fig. 1, it is evident that PEB temperatures greater than 90°C and durations longer than 3 min are unnecessary. The effect of baking the exposed images is to decrease the sensitivity parameters, corresponding to an increased sensitivity, but not to an equivalent extent for both of D0 and D0.5. Thus, though the chemical amplification within these systems is evident it is not uniform at all compositions.For resists containing up to 10% epoxystyrene, baking results in a lesser contrast. At higher epoxystyrene contents the contrasts are marginally enhanced, baking having little or no effect on D0 at the higher epoxystyrene contents. At an epoxystyrene content of 30% baking no longer has any noticeable effect, though one is again apparent for the formulation involving the poly(4-epoxystyrene) homopolymer.Only those resists containing less than 10% epoxystyrene show PEB effects that are comparable to the amplifications observed for the epoxy novolac systems.16 Thus, for copolymer compositions that are lithographically useful, P2 to P6, the present resist system is notably more tolerant of processing variations than are the epoxy novolac Fig. 1 Representative contrast curves of PAG sensitised resists: formulations. Whilst not asserting a PEB to be unnecessary, (a) polymer P3 baked at 120 °C for 0 (&), 180 ($), 360 (+) and 540 s it is nonetheless apparent that to all intents and purposes the (,); (b) polymer P6, unbaked (&) and baked at 90 ($), 120 (+) and 150 °C (,) for 180 s maximum attainable level of crosslinking is achieved within the unbaked systems.the contrast curves from the dose axis at low doses, a character- The effect of variations in PAG loading istic of resist systems that undergo a chain crosslinking process, is discernible for all of the copolymers P1 to P5 and for the Fig. 3 depicts the variation of the sensitivity of the copolymer P6 with PAG concentration.A sharp increase in sensitivity baked system of P6. The contrast curves for the remaining copolymers display a more acute departure from the dose axis, results from the inclusion of even the smallest amounts of the PAG, but for the unbaked systems the effect then seems to be similar to that which is shown later in Fig. 5. The lithographic sensitivities of the resists increase sharply with the epoxide more or less invariant up to a content of about 2%.In contrast, for the baked systems a steady increase in sensitivity is evident content but there is an accompanying loss of contrast. A plot of sensitivity against mole fraction of 4-epoxystyrene within over the composition range investigated. Accordingly, the greatest chemical amplification is evident at a PAG content of the copolymers, shown in Fig. 2, levels off acutely at an epoxide content of ca. 10%; the sharpness of the knee in the curve is 2%. The corresponding contrast variations are shown in Fig. 4. For both the unbaked and baked systems, a small but steady striking, being far more pronounced than those observed for the one component, single-stage crosslinking resists such as increase with PAG loading is evident following the initial sharp drop from the contrast of the unloaded system.the chlorostyrene/methylstyrene copolymer systems.14 Such a sensitivity variation might be expected for a resist system that The relatively insensitive system in which no PAGis included has a contrast value of 2.3. This is characteristic of the optimum crosslinks through a sensitised chain reaction.However, the contrast variation is also notably different from that observed that can be obtained from a single-stage crosslinking resist J. Mater. Chem., 1997, 7(3), 421–427 423the chemical amplification principle.16 s=e-ar (1) The sol fraction remaining in the irradiated polymer is s, and r is the absorbed dose in Mrad.The parameter a is given by eqn. (2) in which G is the radiation chemical yield for chain initiation (assumed to be the number of protons deriving from the photoacid generator that are effective in initiating the crosslinking process per 100 eV of energy absorbed), n is the number of polymer chains that are linked in the ensuing crosslinking, and M� n is the initial number-average molecular mass of the polymer.a=1.04×10-6GnM� n (2) Rearranging eqn. (1) gives eqn. (3). ln s=-ar (3) This simple model predicts that plots of ln s vs. r would be Fig. 3 Variation of lithographic sensitivity of polymer P6 with PAG linear with zero intercept, and knowledge of M� n allows the loading, ($) unbaked and (&) baked for 180 s calculation of the product parameters, Gn, from their slopes.These values are listed in Table 1 and the chemical amplifi- cation effect is evident from a comparison of the values for the baked and unbaked resists. The effect is much more pronounced for the systems of lithographic interest in which the epoxystyrene content exceeds ca. 10%. It is usual, when discussing the lithographic response of negative-working resists, to employ equations expressed in terms of the gel fraction, g, since this can be related directly to the thickness, t, of the resist layer that remains after development, normalised to its original spun thickness, t0.Thus, since s=1-g and g=t/t0 it follows that s=1-t/t0. Thus, the lithographic data can readily be plotted in accordance with eqn. (3). Fig. 6 shows representative plots derived from the primary data of the contrast curves shown in Fig. 1 for the Fig. 4 Variation of lithographic contrast of polymer P6 with PAG loading, ($) unbak&) baked for 180 s with anormal (most probable)molecular mass distribution.17,18 The contrast curve for this resist is shown in Fig. 5. Discussion We have previously adapted the Charlesby theory of polymer network formation by an uninhibited radiation-induced chain reaction19 to derive a simple model, shown as eqn.(1), for the lithographic performance of negative-working resists based on Fig. 6 Charlesby plots of data of contrast curves represented in Fig. 1 Fig. 5 Contrast curve for the unsensitised resist based on polymer P5 424 J. Mater. Chem., 1997, 7(3), 421–427resist formulations P2 and P6.The curves are linear up to content of the copolymers. A linear regression analysis of the log 10D0.5 vs. log10x plot of Fig. 7 reveals a slope of -1.99. normalised thicknesses remaining in excess of 0.7, beyond which they show a positive deviation from linearity. The onset The plot of D0.5 vs. x-2 of Fig. 8 shows the accuracy of the correlation over the data points of lithographic interest. of this deviation generally appears at lower doses for the unbaked systems. It is attributed to localised reductions in It was previously shown that, according to the simple model represented by eqn.(1), the contrast, c, should always be 0.8 epoxide groups to levels at which the active centres of crosslinking become effectively trapped at voids. whilst, at the same time, it was acknowledged that for the epoxy novolac systems this apparently represented a minimum With the exception of the plot for the poly(4-epoxystyrene) homopolymer, P1, the plots for copolymers with epoxystyrene value.16 From Table 1 it is apparent that this same minimum value applies to these systems.However, it is clear that the contents greater than 8% displayed small positive intercepts ranging from about 0.05 to ca. 0.25. Within this range there epoxystyrene homopolymer is the only one to which the value 0.8 actually applies, and that with decreasing epoxystyrene was no apparent order to indicate a correlation with the epoxystyrene content of the copolymers, but it can nonetheless content within the copolymers, the contrast steadily increases.If eqn. (4) is used as the premise for the derivation of an be inferred that the model for the copolymers should be modified to accommodate a small correction factor, K, as expression for contrast, taken to be the slope of the contrast curve at the dose required for 50% gelation, then it is readily shown in eqn. (4), the magnitude of which would be no greater than 1.5. The significance that can be attached to the need for shown that eqn.(7) holds. this correction is that the apparent gel dose of the copolymer dg/d log10r=2.303 Kar e-ar (7) resists is marginally suppressed, an effect that can be attributed to the irregular distribution of crosslinking points along the By substituting r=R0.5, it follows that contrast is given by eqn. (8). polymer chain that results from a statistical copolymerisation process.The irregular distribution is itself a source of structural c=0.8+1.15 ln K (8) voids at which active centres might be trapped. This concept accords with the Charlesby models of radiation-induced Comparison of eqn. (8) with Fig. 9, a plot of c vs. the reciprocal of the mol fraction, x, of epoxystyrene in the copolymer, crosslinking reactions in which the processes are eventually terminated at centres from which further growth is inhibited indicates that there is a rough correlation between K and composition.The slope of this plot when it is equated to 1.15 for any one of several reasons, and which are represented by the generalised formula of eqn. (4). ln K leads to eqn. (9). K=e0.047/x (9) s=Ke-ar (4) For ease of reference whilst following the ensuing kinetic argument, an adaptation of Scheme 1 to represent radiationinduced crosslinking in the copolymer resists is shown in Scheme 3, within which Ox represents an oxirane group, C+ propagating carbonium ions and i is the associated extent of crosslinking, which in the limit assumes the average value n, i.e. 1in. PAG e-T H+ H++Ox C0+ CA G Ci-1++Ox Ci+ CA Scheme 3 Although values of G have not been determined it is reasonable to assume that they are proportional both to the PAG loading and to the concentration of epoxide groups since the addition of a proton to an oxirane has a significant energy of activation of 25 kJ mol-1.20 The PAG loadings have been Fig. 7 Log–log plot of the variation of lithographic sensitivity with maintained at 4% throughout the series of resists represented copolymer composition in Table 1.G is therefore proportional to the epoxystyrene content within the copolymers. The length of the ensuing chain crosslinking reaction, n, is again proportional to the concentration of epoxide groups. It follows that the product parameter, Gn, should vary linearly with the square of the mol fraction, x, of epoxystyrene in the copolymers, i.e.Gn=kx2 where k is a proportionality constant. Although the above conclusions can be applied directly to the values of Gn listed in Table 1 it is more informative to relate them back to the lithographic parameters. Thus, substituting s=0.5 at r=R0.5=2D0.5 into eqn. (4) and rearranging leads to eqn. (5). D0.5= ln(0.5/K) 2.08×10-6Gn (5) If K is taken to be 1 then eqn.(5) reduces to eqn. (6). D0.5=3.33×105/Gn=(3.33×105/k)x-2 (6) Eqns. (5) and (6) both indicate that the lithographic sensitivity, Fig. 8 Variation of lithographic sensitivity with copolymer composition plotted in accordance with the form of eqn. (6) D0.5, should vary inversely with the square of the epoxystyrene J. Mater. Chem., 1997, 7(3), 421–427 425mer with a normal molecular mass distribution.19 The broken line represented in Fig. 5 applies to a system which undergoes a radiation-induced chain crosslinking process but which is of the same sensitivity. The more satisfactory fit of the data points to the former model than to the latter is clear. Conclusions It has been demonstrated that statistical copolymers of styrene and 4-epoxystyrene, in formulations with an onium salt photoacid generator, make very sensitive electron-beam resists, even when the epoxystyrene content of the copolymers is quite low.The mathematical model previously developed to correlate the lithographic data for the so-called ‘Hatzakis’ resist based on formulations of epoxy novolacs and a PAG has been extended for application to these systems and a possible explanation for contrast variations has followed. At one Fig. 9 Plot of the variation of contrast with the reciprocalof copolymer extreme of copolymer composition, the systems have been composition shown to behave as chemical amplification resists in an exactly analogous manner to the ‘Hatzakis’ systems, whilst at the other end of the composition scale, their lithographic perform- For copolymers containing 8–30% of epoxystyrene, values of ance is more in accordance with that of an unsensitised, single- K calculated from eqn.(8) are of about the same magnitude step crosslinking system. The chemical amplification effect as those estimated from the intercepts of the Charlesby model within those resists that are of lithographic interest is not as plots though, as the epoxystyrene content drops to lower pronounced as has been observed for the ‘Hatzakis’ systems, values, the value of K, estimated from eqn.(9), increases by an attractive feature with regard to the reproducibility of the an order of magnitude. However, at such low contents of effects of any post exposure bake that would be applied during epoxystyrene it is arguable that the system bears little resem- processing.The wide potential for the further development of blance to the epoxy novolac system upon which it was the resist has been demonstrated. The optimisation of its modelled. Copolymers of M� n approximately 15000 have lithographic performance will need to take into account mol- degrees of polymerisation lying between 100 (epoxystyrene ecular mass considerations and the need to seek an appropriate homopolymer) and 145 [poly(styrene)], corresponding to num- solvent development system but through the present study it bers ofxirane groups per molecule in the range 100 to 11 for has again been shown that resists designed around copolymers copolymers in the lithographically interesting composition offer a flexibility that cannot be obtained from homopolymer range.The remaining copolymers of the series, P7 and P8, systems. contain even fewer oxirane groups, ca. 5 and 2 respectively. Not surprisingly these systems are likely to behave in a similar fashion to poly(styrene) for which sensitisation by a PAG is We thank the EPSRC for the award of a Research Studentship an irrelevance; indeed their lithographic parameters resemble (J.J.M.) and of a Postdoctoral Research Fellowship (G.P-G.C.) those of low sensitivity single-stage crosslinking systems.From We also gratefully acknowledge the assistance of the staff of Table 2, it is evident that the resist based on copolymer P6 the Central Microstructure Facility of the Rutherford Appleton without the inclusion of PAG displays a greater sensitivity Laboratory, in particular Mr Ejaz Huq, for facilitating the than either of these resists.The three resists actually make a microlithographic evaluations. series in which the sensitivities of the unbaked systems increase with increasing epoxystyrene content. Fig. 10 represents a plot of the contrast curve of Fig. 5, which is for the resist P6 References without PAG, in accordance with the Charlesby model for a 1 F.M. Houlihan, E. Reichmanis, L. F. Thompson and radiation-induced single-stage crosslinking reaction of a poly- R. G. Tarascon, in Polymers in Microlithography, ed. E. Reichmanis, S. A. MacDonald and T. Iwayanagi, ACS Symp. Ser., Am. Chem. Soc., 1989, 39, 412. 2 S. A. MacDonald, N. J.Clecak, H. R. Wendt, C. G. Wilson, C. D. Snyder, C. J. Knors, N. B. Deyoe, J. G. Mathews, J. R. Morrow, H. E. McQuire and S. J. Holmes, Proc. SPIE, 1991, 2, 1446. 3 T. Hirai, Y. Hatano and S. Nonogaki, J. Electrochem. Soc., 1971, 118, 669. 4 Y. Taniguchi, Y. Hatano, H. Shiraishi, S. Horigome, S. Nonagaki and K. Noraoka, Jpn. J. Appl. Phys., 1979, 18, 1143. 5 L. F. Thompson, J. P. Ballantyne and E.D. Feit, J. Vac. Sci. T echnol., 1975, 12, 1280. 6 S. Imamura, J. Electrochem. Soc., 1979, 126, 1628. 7 R. G. Tarascon, M. A. Hartney and M. J. Bowden, inMaterials for Microlithography, ed. L. F. Thompson, C. G. Wilson and J. M. J. Fre� chet, ACS Symp. Ser. 266, Am. Chem. Soc.,Washington, DC, 1984. 8 M. A. Hartney, R. G. Tarascon and A. E. Novembre, J. Vac. Sci.T echnol. B, 1985, 3, 360. 9 R. G. Jones, Y. Matsubayashi, P. Miller Tate and D. R. Brambley, J. Electrochem. Soc., 1990, 137, 2820. Fig. 10 Data taken from the contrast curve of Fig. 5 plotted in 10 K. J. Stewart, M. Hatzakis, J. M. Shaw and D. E. Seeger, J. Vac. Sci. T echnol. B., 1989, 7, 1734. accordance with the Charlesby model for a single-stage crosslinking reaction (—) compared with a similar representation for a system of 11 M. Hatzakis, K. J. Stewart, J. M. Shaw and S. A. Rishton, J. Electrochem. Soc., 1991, 138, 1076. the same sensitivity which undergoes a chain crosslinking process (,) 426 J. Mater. Chem., 1997, 7(3), 421–42712 P. Argitis, I. Raptis, C. J. Aidinis, N. Glezos, M. Baciocchi, 17 Ll. G. Griffiths, R. G. Jones and D. R. Brambley, Polym. Commun., 1988, 29, 173. J. Everett and M. Hatzakis, J. Vac. Sci. T echnol. B., 1995, 13, 3030. 13 R. Truxa and M. Suchopa�rek,Makromol. Chemie, 1990, 191, 1931. 18 D. R. Brambley, R. G. Jones, Y. Matsubayashi and P. Miller Tate, J. Vac. Sci. T echnol. B, 1990, 8, 1412. 14 R. G. Jones, P. C. Miller Tate and D. R. Brambley, J.Mater. Chem., 1991, 1, 401. 19 A. Charlesby, Atomic Radiation and Polymers, Pergamon Press, Oxford, 1960. 15 A. Novembre and T. N. Bowmer, in Materials for Microlithography, ed. L. F. Thompson, C. G. Wilson and 20 Y. I. Estrin and S. G. Entelis, Polym. Sci. USSR, 1968, 10, 3006; 1969, 11, 1286. J. M. J. Fre� chet, ACS Symp. Ser. 266, Am. Chem. Soc.,Washington, DC, 1984. 16 P. C. Miller Tate, R. G. Jones, J. Murphy and J. Everett, Paper 6/06322E; Received 13th September, 1996 Microelectronic Eng., 1995, 27, 409. J. Mater. Chem., 1997, 7(3), 421–4

ISSN:0959-9428    

DOI:10.1039/a606322e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Synthesis and non-linear properties of disubstituted diphenylacetylene and related compounds Koichi Kondo,*a Takumi Fujitanib and Noriaki Ohnishib aDepartment of Chemistry, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525, Japan bDepartment of Applied Fine Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan A variety of disubstituted diphenylacetylenes and related compounds have been synthesized by a modified Horner–Emmons reaction, and their second harmonic generation (SHG) has been evaluated by the Kurtz powder method.The diphenylacetylenes with weak electron-donating and -withdrawing groups are found to be efficient for SHG, as well as having the lowest cut-off wavelength. In recent decades, much attention has been focused on non- (5, 7, 9 and 13) were prepared from various aldehydes (Scheme 2).linear materials from both theoretical and practical points of Diphenylbutadiyne 7 is considered to be a potentially useful view. In particular, second harmonic generation (SHG) based compound for third harmonic generation (THG) since some on organic compounds is interesting because of the large nonpoly( diacetylene)s synthesized from butadiynes have been linear susceptibilities produced by intramolecular charge transfound to exhibit large THG properties.10 Moreover, the ter- fer (ICT) in p-conjugated systems, which is substantially minal acetylene 9 is attractive as a potential monomer for different from inorganic materials.1 Most SHG active organic polymerization by W, Ta11 and/or Rh catalysts12 into a poly- compounds are based on p-nitroaniline derivatives, despite the (phenylacetylene) system with similar properties.recent discovery of non-linear rigid ICT acetylene frameworks.2 The SHG intensity of compounds 3, 5, 7, 9 and 13 relative Disubstituted diphenylacetylene derivatives, however, have not to urea was determined by the Kurtz powder method.13 The been studied in terms of their non-linear properties, except for results are summarized in Table 1 (for 3) and Table 2 (for 5, 7, a few examples such as 1-(4-methoxyphenyl)-2-(4-nitrophe- 9 and 13).Table 1 shows only the SHG active phenylacetylenes nyl)acetylene3,4 and 1-(4-bromophenyl)- and 1-(4-iodophenyl)- out of more than seventy compounds prepared via the reported 2-(4-nitrophenyl)acetylene,5 due to the tedious preparation method.The fact that a number of diphenylacetylenes are based on the oxidative coupling of cuprous arylacetylides with SHG active indicates that they tend to adopt the non-centro- aryl iodides. Although this classical oxidative method has symmetric crystal packing essential for SHG, a suggestion that now been superseded by the recently developed Pd-catalysed is supported by X-ray crystallographic analysis of these mol- coupling of ethynylbenzene derivatives with iodo- or bromoecules. 14 The large number of chloro-substituted compounds substituted aromatic compounds, the latter is limited to pthat exhibit SHG also indicates that weak dipole polarization conjugated systems.6 may favour non-centrosymmetric crystal packing, which can While searching for another preparation of diphenylacetyrely on a ICT structure linked to the cut-off wavelength as lenes, we realised that a modified Horner–Emmons reaction shown in the weak dipole–dipole interaction of SHG active 3- has previously proved useful for triple bond formation and methyl-4-nitropyridine N-oxide.15 The cut-off wavelength of has afforded a variety of pyridylphenylacetylenes.7 the chloro-substituted compounds 3 was as low as that of Here we describe the synthesis of 4,4¾-disubstituted diphenyl- stilbene derivatives.16 In general, compounds 3 with weak acetylenes and related compounds based on a modified electron-withdrawing and -donating groups such as Cl and Horner–Emmons reaction, together with their SHG properties.Results and Discussion Zimmer et al. reported that phosphonate carbanions couple with aryl aldehydes under mild basic conditions to give chlorostilbenes or diphenylacetylenes.8 This method, however, has not been used widely because of the sensitive reaction conditions required for the preparation of the starting hydroxy phosphonate, which is thermally liable and prone to rearrangement to the phosphate.9 Therefore the temperature control, as well as choice of solvent, was examined.Diphenyl phosphite was allowed to react with the appropriate 4-substituted benzaldehydes in THF for a few hours below 25°C to afford diphenyl hydroxy(aryl)methylphosphonates 1, which were converted to the chloro compounds 2 by treatment with POCl3–PhNEt2 for 1 h at 90°C.Thus, further 4-substituted benzaldehydes and 2 were subsequently treated with 2 equiv. of ButOK in THF for 3 h at room temperature to afford the 4,4¾-disubstituted diphenylacetylenes 3 X CHO X OH P O OPh OPh X Cl P O OPh OPh X Y 1 POCl3 PhNEt2 CHO Y (PhO)2P(O)H 2 ButOK 2 3 Scheme 1 (Scheme 1). Based on this reaction, the related compounds J. Mater. Chem., 1997, 7(3), 429–433 429NO2 NO2 S S X Cl P O OPh OPh Y X S S CHO CHO Y CHO CHO H CH(OEt)2 OHC 2 X = Cl, Br, CN, NO2, MeO 4 O2N CH(OEt)2 4 ButOK 6 X 8 10 H 2 ButOK O2N CHO 5 7 12 13 O2N 2 ButOK 2 ButOK (X = NO2) H+ 9 OMe 11 2 (X = OMe) 2 ButOK (X = NO2) Scheme 2 MeO exhibit a hypsochromic shift in the cut-off wavelength 65 times as active as urea.However, when recrystallized from ethanol, as in our study, they are only twice as active as urea.(337 nm) that arises from the weak ICT structure needed for SHG, as compared with the bathochromic shift for compounds Such solvent effects may be due to crystal polymorphism related to crystal packing, which can vary when different with strong electron-withdrawing and -donating groups (590 nm for nitro and dimethylamino substitutents) (Table 3).solvents are used during crystallization. Further studies involving X-ray crystallography are currently in progress. No significant effect of the chain length of the substituted alkoxy groups on SHG was found. Additional triple bond conjugation was not significantly effective for SHG, as shown Experimental for the nitro- and methoxy-substituted compounds 3 (X= NO2, Y=MeO): 7 (X=MeO, Y=NO2) and 13, in which SHG THF was distilled over sodium and LiAlH4. 4- Alkoxybenzaldehydes were obtained by the reaction of active 3 shows a decrease in the cut-off wavelength, while SHG inactive butadiyne 7 is much more highly conjugated than the 4-hydroxybenzaldehyde with the relevant alkyl bromide [Me(CH2)nBr; n=4–11] in DMF in the presence of sodium extended p-conjugated diphenylacetylene type compound 13 (Tables 1 and 2).SHG active 5 is of interest because of its hydride at 50°C for 24 h. 6,6-Diformyl-1,4-dithiafulvene 4,18 4-ethynylbenzaldehyde 819 and 4-(diethoxymethyl)benzal- triangular structure, which is similar to SHG active L-type methanediamine derivatives.17 dehyde 1020 were prepared by literature methods. 4-Substituted 3-phenyprop-2-ynal 6 was obtained by the formylation of 4- Sample manipulation affects SHG significantly. For example, 1-(4-methylthio- and 1-(4-methoxy-phenyl)-2-(4-nitrophe- substituted ethynylbenzene,21 which was derived from 4-substituted trimethylsilylethynylbenzene6a or 4-aryl-2-methylbut-3- nyl)acetylene which were chromatographed on silica gel2 and recrystallized from methylcyclohexane,3 respectively, are 50 to yn-2-ol.22 430 J.Mater. Chem., 1997, 7(3), 429–433Table 1 Relative SHG powder efficiency of 3 Table 3 Cut-off wavelength for varied substitution in compound 3 3 3 cut-off cut-off X Y SHGa wavelength/nm X Y wavelength/nm NO2 F 418 NO2 SMe 2.7 462 NO2 OMe 2.0 425 NO2 OMe 425 NO2 NEt2 590 CN OC5H11 7.5 373 CN OC6H13 0.1 375 CN F 350 CN OMe 374 CN OC7H15 4.0 375 CN F 0.1 350 CN NEt2 474 Br F 324 CN Br 0.1 406 CN NMe2 0.1 457 Br OMe 347 Br NEt2 433 CN NEt2 0.1 474 Cl SMe 0.1 360 Cl F 320 Cl OMe 337 Cl OMe 0.1 337 Cl OEt 0.1 343 Cl NEt2 427 Cl OPr 0.1 332 Cl OBu 0.1 346 Cl OC5H11 0.1 337 Cut-off wavelength Cl OC6H13 2.8 350 Cl OC7H15 0.1 348 The cut-off wavelength was determined from 95% of the Cl OC8H17 0.8 347 transmittance, which was measured for a 1 mM MeCN solution Cl OC10H25 0.9 342 of the compounds.Cl OC12H25 0.5 383 Cl F 0.1 320 Diphenyl hydroxy(4-nitrophenyl )methylphosphonate 1 Cl NMe2 4.7 433 Cl NEt2 0.1 427 (X=NO2) Br OMe 1.4 347 To a solution of 4-nitrobenzaldehyde (12 g, 80 mmol) in dry Br OC6H13 0.1 352 Br OC7H15 0.1 351 THF (30 cm3) was added dropwise a solution of diphenyl Br OC8H17 0.1 428 phosphite (18.7 g, 80 mmol) in dry THF (20 cm3) over 30 min, Br NEt2 0.1 433 and the reaction was stirred for 3 h at room temperature.After evaporation of the solvent, the residue was recrystallized from aRelative to urea. ethanol to give the product (65%), mp 125 °C; dH[(CD3)2SO] 4.65 (1H, s, OH), 5.38 (1H, d, CH, JHP12†), 6.90–7.41 (10H, Table 2 Relative SHG powder efficiency of extended p-conjugated m, aromatic H), 7.68 (2H, d, aromatic H), 8.18 (2H, d, aromatic systems H); nmax(KBr)/cm-1 3280s (OH), 1520s and 1330s (NO2 ), 1250m (PNO), 1060m, 1020m and 960m (P–O) (Found: C, cut-off 59.15; H, 4.17; N, 3.60.C19H16NO6P requires C, 59.22; H, 4.19; wavelength/ extended p-conjugated system SHGa nm N, 3.64%). Diphenyl chloro(4-nitrophenyl )methylphosphonate 2 (X=NO2) 1 (X=NO2 ) (9.3 g, 24.1 mmol) was treated with 25 cm3 of 0.1 520 POCl3 in the presence of N,N-diethylaniline (2 cm3) for 1 h at 90°C.After evaporation of the solvent and addition of ice– water, the reaction was extracted with CH2Cl2, and the extracts were washed with aqueous sodium hydrogen carbonate and 5.0 483 dried over MgSO4. The solvent was evaporated in vacuo and the residue recrystallized from ethanol to give the product (84%), mp 121 °C; dH[(CO3)2SO] 5.64 (1H, d, CH, JHP 15), 1.0 475 7.20–7.65 (10H, m, aromatic H), 8.08 (2H, d, aromatic H), 8.52 (2H, d, aromatic H); nmax(KBr)/cm-1 1520s and 1350s 1.5 467 (NO2), 1270m (PNO), 1070m, 1020m and 960m (P–O) (Found: C, 56.71; H, 3.68; N, 3.37.C19H15NO5PCl requires C, 56.52; H, 3.74; N, 3.47%). 0 485 Diphenyl chloro(4-methoxyphenyl )methylphosphonate 2 0 456 (X=MeO) Yield 27%, mp 117°C; dH[(CD3)2SO] 3.85 (3H, s, CH3 ), 5.20 0 470 (1H, d, CH, JHP 14), 6.80–7.65 (14H, m, aromatic H) (Found: C, 61.35; H, 4.96. C20H18O4PCl requires C, 61.78; H, 4.63%). aRelative to urea. Diphenyl chloro(4-cyanophenyl )methylphosphonate 2 (X=CN) Second harmonic generation measurements The samples were ground with a mortar and pestle, meshed Yield 68%, mp 125°C; dH[(CD3 )2SO] 5.23 (1H, d, CH, JHP 15), 6.80–7.30 (10H, m, aromatic H), 7.65 (4H, m, aromatic to 75 to 100 mm and fixed on a glass slide by tape.The slide was irradiated by a Nd-YAG laser (l=1064 nm, pulse width H) (Found: C, 62.26; H, 3.92; N, 3.68. C20H15NO3PCl requires C, 62.59; H, 3.94; N, 3.65%). 350 ps, power density 5 GWcm-2, spot size 0.8 mm) and the intensity of SHG light (532 nm) was monitored by a photodiode and compared with the SHG intensity of urea.† J values given in Hz. J. Mater. Chem., 1997, 7(3), 429–433 431Diphenyl chloro(4-chlorophenyl )methylphosphonate 2 (X=Cl ) 1.32 (6H, t, CH3), 3.75 (4H, q, CH2 ), 5.50 (1H, s, CH), 7.60 (2H, d, aromatic H), 8.15 (2H, d, aromatic H).The acetal (3 g, Yield 56% mp 91°C; dH[(CD3)2SO] 5.17 (1H, d, CH, JHP 14), 12 mmol) was hydrolysed with 0.5 M sulfuric acid (50 cm3) at 6.90–7.50 (14H, m, aromatic H) (Found: C, 57.94; H, 3.67. 110°C for 40 min, and the reaction was extracted with CH2Cl2 C19H15O3PCl2 requires C, 58.04; H, 3.85%). to give 3-(4-nitrophenyl)prop-2-ynal in 54% yield, mp 95°C; dH(CDCl3) 7.78 (2H, d, aromatic H), 8.30 (2H, d, aromatic Diphenyl bromo(4-bromophenyl)methylphosphonate 2 (X=Br) H), 9.50 (1H, s, CH); nmax(KBr)/cm-1 2260m (COC), 1620s (CNO) (Found: C, 61.50; H, 3.05; N, 7.87.C9H5NO3 requires Yield 29%, mp 107 °C; dH[(CD3)2SO] 5.17 (1H, d, CH, JHP C, 61.71; H, 2.88; N, 8.00%). 14), 6.50–7.30 (10H, m, aromatic H), 7.48 (4H, s) (Found: C, 51.84; H, 3.40.C19H15O3PClBr requires C, 52.14; H, 3.45%). 1-(4-Ethynylphenyl)-2-(4-nitrophenyl )acetylene 9 (X=NO2 ) 1-(4-Methoxyphenyl )-2-(4-nitrophenyl )acetylene 3 Compound 2 (X=NO2) (2.01 g, 4.9 mmol) and 4-ethynylben- (X=NO2, Y=MeO) zaldehyde 8 (0.65 g, 4.9 mmol) were treated with ButOK (1.20 g, 10.7 mmol) in THF (30 cm3) for 3 h at room tempera- Compound 2 (X=NO2) (1.25 g, 3.07 mmol) and 4-methoxy- ture.After evaporation of the solvent, the residue was extracted benzaldehyde (0.60 g, 4.0 mmol) in THF (30 cm3) were treated with CH2Cl2, and the solution dried over MgSO4. The solvent with ButOK (1.0 g, 8.9 mmol) for 3 h at room temperature. was removed and the residue recrystallized from ethanol to After evaporation of the solvent, water (20 cm3) was added to give the product in 44% yield, mp 211 °C; dH(CDCl3 ) 3.23 the residue, the aqueous mixture was extracted with CH2Cl2, (1H, s, CH), 7.52 (2H, d, aromatic H), 7.70 (2H, d, aromatic and the organic fractions were dried over MgSO4 .The solvent H), 8.13 (2H, d, aromatic H), 8.28 (2H, d, aromatic H); was removed in vacuo and the residue was recrystallized nmax(KBr)/cm-1 3240m (C–H), 2200m (COC), 1500s and from ethanol to give the product in 58% yield, mp 115 °C; 1335s (NO2) (Found: C, 77.62; H, 3.60; N, 5.58.C16H9NO2 dH(CDCl3 ) 3.90 (3H, s, CH3), 7.09–8.24 (8H, m, aromatic H); requires C, 77.72; H, 3.67; N, 5.67%). nmax(KBr)/cm-1 2210m (COC), 1510s and 1335s (NO2) (Found: C, 71.06; H, 4.39; N, 5.50. C15H11NO3 requires C, 1-(4-Cyanophenyl)-2-( 4-ethynylphenyl )acetylene 9 (X=CN) 71.14; H, 4.38; N, 5.53%).Mp 207 °C; dH(CDCl3) 3.10 (1H, s, CH), 7.38 (4H, m, aromatic 1-(4-Cyanophenyl )-2-(4-pentyloxyphenyl ) acetylene 3 H), 7.52 (4H, m, aromatic H); nmax(KBr)/cm-1 3225m (C–H), (X=CN, Y=C5H11O) 2220m (CON), 2200 (COC) (Found: C, 89.63; H, 3.80; N, 6.05. C17H9N requires C, 89.84; H, 3.99; N, 6.16%). Yield 34%, mp 83°C; dH(CDCl3 ) 0.63–2.65, (8H, m, CH2), 3.65 (3H, t, CH3), 6.54–7.25 (8H, m, aromatic H); 6,6-Bis[ 2-(4-nitrophenyl ) ethynyl]-1,4-dithiafulvene 5 nmax(KBr)/cm-1 2940s, 2910s and 2840s (C–H), 2210m (CON), 2200m (COC) (Found: C, 82.64; H, 6.63; N, 4.57.C20H19NO Compound 2 (X=NO2 ) (1.61 g, 4 mmol) and 6,6-diformyl-1,4- requires C, 83.01; H, 6.62; N, 4.84%). dithiafulvene (0.30 g, 1.7 mmol) were treated with ButOK (1.0 g, 9.2 mmol) in THF (50 cm2) for 4 h at room temperature. After evaporation of the solvent, the residue was extracted 1-(4-Chlorophenyl )-2-(4-dimethylaminophenyl )acetylene 3 with CH2Cl2 and the solution dried over MgSO4.The solvent (X=Cl, Y=NMe2 ) was removed and residue recrystallized from ethanol to give Yield 32%, mp 150 °C; dH(CDCl3) 2.03 (6H, d, CH3) 6.55–7.43 the product in 15% yield, mp 115 °C; dH(CDCl3 ) 7.15–8.25 (8H, m, aromatic H); nmax(KBr)/cm-1 2890s, 2850s and 2800s (8H, m, aromatic H); nmax(KBr)/cm-1 2200m (COC), 1510s (C–H), 2200m (COC) (Found: C, 75.10; H, 5.37; N, 5.17. and 1330s (NO2) (Found: C, 58.52; H, 2.85; N, 6.52.C16H14NCl requires C, 75.14; H, 5.52; N, 5.48%). C20H12N2O4S2 requires C, 58.81; H, 2.96; N, 6.86%). 1-(4-Bromophenyl )-2-(4-methoxyphenyl ) acetylene 3 1-(4-Methoxyphenylethynyl )-4-(4-nitrophenylethynyl )benzene (X=Br, Y=MeO) 13 Yield 26%, mp 155 °C; dH(CDCl3) 3.86 (3H, s, CH3 ) 6.36–7.50 Compound 2 (X=NO2) (2.01 g, 5.01 mmol) and compound (8H, m, aromatic H); nmax(KBr)/cm-1 2970m, 2930m and 10 (1.0 g, 4.81 mmol) were treated with ButOK (1.2 g, 2840m (C–H), 2200m (COC) (Found: C, 62.48; H, 3.77. 10.7 mmol) in THF (30 cm3) for 3 h at room temperature. C15H11OBr requires C, 62.74; H, 3.86%). After evaporation of the solvent the residue was stirred with 1 M hydrochloric acid (50 cm3) for 30 min, then the reaction 3-(4-Nitrophenyl )prop-2-ynal 6 (Y=NO2 ) was extracted with CH2Cl2, and the organic fractions dried over MgSO4 .The solvent was removed under reduced pressure, 4-Bromonitrobenzene (50 g, 247 mmol) and 2-methylbut-3-yn- and the residue recrystallized from ethanol to give 1-(4- 2-ol (25 g, 297 mmol) were refluxed for 2 h in triethylamine formylphenyl)-2-(4-nitrophenyl)acetylene 12 (X=NO2) in (500 cm3).The solvent was evaporated under reduced pressure 60% yield. Compound 12 (X=NO2) (0.15 g, 1 mmol) and and the residue was recrystallized from benzene to give 4-(4- compound 2 (X=MeO) (0.39 g, 1 mmol) were similarly treated nitrophenyl)-2-methylbut-3-yn-2-ol in 79% yield, mp 102 °C; with ButOK (0.23 g, 2.02 mmol) to give the final product in dH(CDCl3 ) 1.62 (6H, s, CH3 ), 2.17 (1H, s, OH), 7.50 (2H, d, 20% yield, mp 193 °C; dH(CDCl3) 6.75–7.50 (8H, m, aromatic aromatic H), 8.13 (2H, d, aromatic H).The alcohol (15 g, H), 7.55 (2H, d, aromatic H), 8.10 (2H, d, aromatic H); 73 mmol) and ButOK (2 g, 17.8 mmol) were refluxed for 50 min nmax(KBr)/cm-1 2200m (COC), 1505s and 1335s (NO2) in ButOH (50 cm3), the solvent was evaporated under reduced (Found: C, 78.05; H, 4.18; N, 3.85.C23H15NO3 requires C, pressure and the residue was recrystallized from ethanol 78.17; H, 4.28; N, 3.96%). to give 1-ethynyl-4-nitrobenzene in 67% yield, which can also be prepared from 1-bromo-4-nitrobenzene and tri- 1-(4-Methoxyphenyl)-4-(4-nitrophenyl )buta-1,3-diyne 7 methylsilylacetylene.6a Thus, 1-ethynyl-4-nitrobenzene (1.48 g, (X=MeO, Y=NO2 ) 10.0 mmol) and triethyl orthoformate (30 cm3) were heated in the presence of zinc iodide (0.14 g, 0.4 mmol) at 140 °C for 2 h 3-(4-Nitrophenyl)prop-2-ynal (0.175 g, 1 mmol) and comto remove ethanol by distillation.The residue was distilled pound 2 (X=MeO) (0.388 g, 1 mmol) were treated with ButOK under reduced pressure to give 3-(4-nitrophenyl)prop-2-ynal (0.25 g, 2.2 mmol) in THF (30 cm3) for 4 h at room temperature. After evaporation of the solvent, the residue was dissolved diethyl acetal (bp 150 °C at 1 torr) in 60% yield; dH(CDCl3) 432 J.Mater. Chem., 1997, 7(3), 429–4337 K. Kondo, N. Ohnishi, K. Takemoto, H. Yoshida and K. Yoshida, in CH2Cl2 and dried over MgSO4. The solvent was removed J. Org. Chem., 1992, 57, 1622. in vacuo and the residue was recrystallized from benzene to 8 H. Zimmer, P. J. Berez, PO. J. Maltenieks and M. W. Moor, J. Am. give the title compound in 20% yield, mp 244 °C; dH(CDCl3) Chem.Soc., 1965, 87, 2777. 3.98 (3H, s, CH3), 6.89 (2H, d, aromatic H), 7.57 (2H, d, 9 A. N. Pudovik and I. V. Konovalova, Synthesis, 1979, 81. aromatic H), 7.75 (2H, d, aromatic H), 8.33 (2H, d, aromatic 10 B. I. Greene, J. Orenstein, R. R. Millard and L. R. Williams, Chem. Phys. L ett., 1987, 139, 381. H); nmax(KBr)/cm-1 2200m (COC), 1510s and 1335s (NO2) 11 T.Msuda, N. Sasaki and T. Higashimura, Macromolecules, 1975, (Found: C, 73.30; H, 3.98; N, 4.80. C17H11NO3 requires C, 8, 717. 73.64; H, 4.00; N, 5.05%). 12 M. Tabata, Y. Yang and K. Yokota, Polym. J., 1990, 22, 1105. 13 S. K. Kurtz and T. T. Perry, J. Appl. Phys., 1968, 39, 3798. 14 A. A. Espiritu and J. G. White, Acta Crystallogr., Sect. B, 1977, References 33, 3899. 15 J. Zyss and D.S. Chemla, J. Chem. Phys., 1981, 74, 4800. 1 Nonlinear Optical Properties of OrganicMolecules and Crystals, ed. 16 A. Dulcic, C. Flytzanis, C. L. Tang, D. Pepin, M. Fetizon and D. S. Chemela and J. Zyss, Academic, Orland, 1987, vol. 1, p. 679. Y. Hoppilliad, J. Chem. Phys., 1981, 74, 1559. 2 A. E. Stiegman, E. Graham, K. J. Perry, L. R. Khundkar, 17 H. Yamamoto, S. Katogi, T.Watanabe, S. Miyata and T. Hosomi, L.-T. Cheng and J. W. Perry, J. Am. Chem. Soc., 1991, 113, Appl. Phys. L ett., 1992, 60, 24. 7658. 18 C. Reichardt, B-V. Herget, M. Schulz, W. Massa and S. Peschel, 3 T. Kurihara, H. Tabei and T. Kaino, J. Chem. Soc., Chem. T etrahedron L ett., 1989, 30, 3521. Commun., 1987, 959. 19 W. B. Austin, N. Bilow, W. J. Kellefhan and K. S. Y. Lau, J. Org. 4 H. Tabei, K. Kurihara and T. Kaino, Appl. Phys. L ett., 1987, 50, Chem., 1981, 48, 2280. 1855. 20 K. Ichimura and Y. Nishio, J. Polym. Sci., 1987, A25, 1579. 5 Y.Wang, W. Tam, S. H. Stevenson, R. A. Clement and J.Calabrese, 21 Org. Synth., Coll. vol. IV, 801. Chem. Phys. L ett., 1988, 148, 136. 22 S. J. Havens and P. M. Hergenrother, J. Org. Chem., 1985, 50, 6 (a) S. Takahashi, Y. Kuroyama, K. Sonogashira and H. Hagihara, 1763. Synthesis, 1980, 627; (b) M. S.Wong and J-F. Nicoud, T etrahedron L ett., 1994, 35, 6113; (c) K. Kondo, S. Yasuda, T. Sakaguchi and Paper 6/06915K; Received 9th October, 1996 M. Miya, J. Chem. Soc., Chem. Commun., 1995, 55. J. Mater. Chem., 1997, 7(3), 429–433 433

ISSN:0959-9428    

DOI:10.1039/a606915k

出版商:RSC    

年代:1997

数据来源: RSC