Fluorescence solvatochromism of nitrodiphenylhexatrienes

Abstract

Examination of the absorption and fluorescence spectra of symmetrically and asymmetrically substituted 4′-nitro derivatives of 1,6-diphenyl-1,3,5,-hexatriene reveals fundamental transformations of photophysical behaviour relative to the parent molecule. The manifestations of this divergence are solvent dependent. In non-polar solvents the primary effect is a reduction of the fluorescence quantum yield to negligible levels. This condition is superseded as solvent polarity rises by the appearance of extensively red-shifted fluorescence. The correlation of this spectral shift (solvatochromism) with macroscopic solvent polarity is evaluated. These distinctive fluorescence properties, together with the complementary but less dramatic variations of absorption spectra, are interpreted in terms of the involvement of substituent associated intramolecular charge-transfer excited states.