Comparative study of the solvent effect on the spectral properties of aminopolyenic molecules with different acceptor substituents

Abstract

The spectral and fluorescent properties of a number of ωω′-bis(aminopolyenyl)ketones (ketocyanines) and ωω′-bis(3-dimethylaminopropen-2-yliden)-alkylidenmalononitriles (dinitriles), being analogues of usual ketocyanines, but containing the dicyanomethylene fragment instead of the carbonyl group, were studied. Specific and nonspecific solvation of dinitriles and corresponding ketocyanines was studied on the basis of the solvatochromic shifts of the absorption spectra. The photophysical data obtained for the different molecular structures were correlated with different empirical parameters, which characterize solvation by organic solvents: the Dimroth-Reichardt ET(30) parameter of the solvating power, the acceptor number AN, the donor number DN, and the constant π* characterizing the solvent polarity and polarizability. A linear dependence of the maximums in the absorption spectra on the acceptor number AN, which characterizes specific solvation, was found for the ketocyanines under study. This indicates that the electrophilic solvation plays a key role in ketocyanine solutions. For dinitriles, the linear dependence of the maximums of the absorption spectra was obtained as f(π*, AN, DN). In the latter case, along with the electrophilic solvation, there is a substantial contribution of nonspecific and nucleophilic solvation.