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 2 were 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 β value of 2b was found to be about 8 times greater than that of pNA. We also performed X-ray crystallographic analysis of 2b and estimated NLO coefficient (d) by the oriented gas model. We found that diagonal component of 2b (d11 = 610 pmV-1) was about 14 times greater than that of 2-methyl-4-nitroaniline and off-diagonal component of 2b (d12 = 155pm V-1) was about 6.5 times greater than that of N-(4-nitrophenyl)-L-prolinol. Compound 2b should be an excellent candidate for NLO applications.
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