Synthesis, structure and solvatochromism of the emission of cyano-substituted oligo(phenylenevinylene)s

Strongly luminescent and highly soluble oligo(phenylenevinylene)s with five benzene rings and cyano groups in different positions of the terminal styr ene units were prepared by means of Horner and Knoevenagel reactions. The s ubstitution pattern - cyanide moieties on the vinyl or on the aromatic regi ons, together with the effect of auxochromic groups - has distinct influenc es on the electronic spectra, particularly on the fluorescence. Polar solve nts induce red shifts and strongly reduce the fluorescence intensity of the vinyl-substituted oligomers. Cya-no substitution increases the electron af finity of the oligomers; this effect is more pronounced for molecules with vinyl cyanides and can be altered by the presence of additional electron-do nating or electron-withdrawing groups. The molecular structures of one olig omer bearing cyano groups on the vinylene segments and one with benzonitril e units have been resolved.