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The molecular arrangement of the extremely uniaxial thin film was determined using X-ray analysis, including grazing incidence wide-angle X-ray scattering. The highly oriented film was obtained by depositing a bisazo dye onto an aligned polytetrafluoroethylene (PTFE) layer via vacuum evaporation, as shown previously. The X-ray analysis indicated that the molecules are arranged in parallel or antiparallel orientations within the unit cell. Moreover, their long axes are parallel to each other within the grains which are uniformly oriented throughout the film. These results confirm the driving force of the orientation reported previously using a molecular dynamics model: dye molecules trapped along the atomic grooves between adjacent PTFE chains serve as nuclei for crystal growth. In addition, the long molecular axes remain parallel to the rubbing direction, although some grains are inclined in the short-axis direction. This molecular arrangement in the film could contribute to a high degree of uniaxial orientation.

Partially fluorinated skeleton of 4-[2-(4-dimethylamino-2,3,5,6-tetrafluorophenyl)ethynyl]-2,3,5,6-tetrafluoro-N,N,N-trimethylanilinium (2) was synthesized as a second-order nonlinear optical (NLO) material to decrease the absorption around 1.3 and 1.5 µm, which deteriorates the device efficiency. Several salts of 2were prepared, and we found that the trifluoromethanesulfonate salt of 2(2b) had a shorter absorption-maximum wavelength compared to that of 4-nitroaniline (pNA). From hyper-Rayleigh scattering (HRS) measurement, the ß value of 2bwas found to be about 8 times greater than that of pNA. We also performed X-ray crystallographic analysis of 2band estimated NLO coefficient (d) by the oriented gas model. We found that diagonal component of 2b(d11=610 pm V-1) was about 14 times greater than that of 2-methyl-4-nitroaniline and off-diagonal component of 2b(d12=155 pm V-1) was about 6.5 times greater than that of N-(4-nitrophenyl)-l-prolinol. Compound 2bshould be an excellent candidate for NLO applications.

1,4-Bis(3-quinolyl)-1,3-butadiyne (DQ) is known to be polymerized in solid state to give the corresponding polydiacetylene. However, the polymer yield of DQ bulk crystals is low. Thus, we prepared several types of DQ crystals by different procedures to find the reason for the low polymer yield. We found three modifications of DQ crystals and they were evaluated by spectroscopic measurements and X-ray diffraction. DQ bulk crystals (Crystal I) and thermally grown DQ crystals on Crystal I (Crystal II) have the same structure classified to Type A, which gives regular polydiacetylene structure in low polymer yields. DQ crystals grown on glass plates by sublimation (Crystal III) belong to the second modification of Type B. DQ nanocrystals prepared by the reprecipitation method (Crystal IV) are Type B, and thermally grown DQ crystals on nanocrystals (Crystal V) are Type C. Crystals of Types B and C could be polymerized in low yields without showing excitonic absorption of polydiacetylene indicating irregular polymerization other than 1,4-addition. For crystals of Type A, we found that the 1,4-addition polymerization proceeded only in near-surface portions of the crystals. It can be plausibly explained that mobile monomers in the near-surface portion are only able to take part in their polymerization, resulting in low polymer conversion. 1,4-Bis(3-quinolyl)-1,3-butadiyne (DQ) is known to be polymerized in solid state to give the corresponding polydiacetylene. However, the polymer yield of DQ bulk crystals is low. Thus, we prepared several types of DQ crystals by different procedures to find the reason for the low polymer yield. We found three modifications of DQ crystals and they were evaluated by spectroscopic measurements and X-ray diffraction. DQ bulk crystals (Crystal I) and thermally grown DQ crystals on Crystal I (Crystal II) have the same structure classified to Type A, which gives regular polydiacetylene structure in low polymer yields. DQ crystals grown on glass plates by sublimation (Crystal III) belong to the second modification of Type B. DQ nanocrystals prepared by the reprecipitation method (Crystal IV) are Type B, and thermally grown DQ crystals on nanocrystals (Crystal V) are Type C. Crystals of Types B and C could be polymerized in low yields without showing excitonic absorption of polydiacetylene indicating irregular polymerization other than 1,4-addition. For crystals of Type A, we found that the 1,4-addition polymerization proceeded only in near-surface portions of the crystals. It can be plausibly explained that mobile monomers in the near-surface portion are only able to take part in their polymerization, resulting in low polymer conversion.

As new ionic organic species for second‐order non‐linear optical (NLO) materials, 4‐{[4‐(dimethylamino)phenyl]ethynyl}phenyltrimethylammonium iodide (1a), 4‐{[4‐(dimethylamino)phenyl]butadiynyl}phenyltrimethylammonium iodide (2a) and their derivatives with 4‐substituted benzensulfonate instead of iodide were successfully synthesized. The transparent wavelength region of 1ais wider than that of a typical NLO molecule, p‐nitroaniline (pNA), whereas 2aand pNA have similar transparent regions. The experimental and calculated first hyperpolarizabilities (β) of 1aand 2awere found to be about 7 and 11 times, respectively, larger than those of pNA. Even when the volume factor was taken into account, the cationic part of 1awas found to be a better second‐order NLO material than pNA derivatives. Four second‐order NLO‐active crystals were found out of 12 salts synthesized. Copyright © 2004 John Wiley & Sons, Ltd.

Several salts of 1-methyl-4-[4-(dimethylamino)phenylethynyl]pyridinium 1, whose ethenyl analogue 2is the cation of DAST (1-methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium p-toluenesulfonate), were synthesized, and these properties were investigated. From a molecular-orbital calculation, the hyperpolarizability (β) of 1was calculated to be about 80% of that of 2. The absorption maximum wavelength of 1is shorter than that of 2. Six SHG active salts based on cation 1, including iodide and 4-substituted benzenesulfonates, were obtained in total. Among them, the crystal structures of p-chlorobenzenesulfonate salt (1c) and p-toluenesulfonate salt (1e) could be analyzed. As a result, these two have almost the same structures, and the off-diagonal second-order nonlinear optical coefficient (d) values were estimated to be about twice as large as those of DAST.

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