Proceedings Article | 27 April 1993
KEYWORDS: Molecules, Optoelectronics, Solid state physics, Nickel, Raman spectroscopy, Liquids, Polarizability, Harmonic generation, Ranging, Crystals
The second hyperpolarizability, (gamma) , of the donor-acceptor polyene compounds (CH3)2N-(CHequalsCH)3-CHO, 3, (CH3CH2CH2CH2)2N- (CHequalsCH)2-CHequalsC(CN)2, 4, the cyanine compound [CH2CH2OCH2CH2-N-(CHequalsCH)3-CHequalsN-CH2CH2OCH2CH2]+ClO4-, 5, and the linear polyenes CH3- (CHequalsCH)n-CH3, where n equals 4, 1, or 5, 2, have been measured by third harmonic generation (THG) at 1907 nm, in a series of solvents ranging in polarity from CCl4 to CH3OH. It was found that 3, with the moderately strong formyl acceptor, had positive values of (gamma) which exhibit a peak as a function of solvent polarity. In contrast, 4, with the stronger dicyanovinyl acceptor, had positive (gamma) in very nonpolar solvents but increasingly negative (gamma) values in solvents of moderate to high polarity. These solvent- dependent hyperpolarizabilities are associated with a change in geometry from a highly bond length alternated, polyene-like structure for the formyl-substituted compound in nonpolar solvents, to a cyanine-like structure, with very little bond length alternation, for the dicyanovinyl-substituted compound in polar solvents.
