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