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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.

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.