Topochemically photoreacted fluorescent dimers of 2,3-dicyanopyrazines

Abstract

Novel fluorescent materials derived from 2,3-dicyanopyrazine were synthesized and subjected to photodimerization reaction. Styryl substituents were attached by Wittig reaction, and the [2+2] photocycloaddition of the 2,3-dicyanopyrazine, either in solution or as a thin film, was studied with irradiation under a high-pressure Hg lamp. The resulting compounds were characterized by H-1 NMR, FT-IR and elemental analysis. Spectral changes of UV-visible absorption intensity and fluorescent intensity were examined at specific exposure intervals. While the cyclobutane ring of dimers induced a discrete pi-conjugation with aryl substituents to show a hypsochromic shift of absorption and emission spectra, the fluorescence intensity was increased and the specific lowest unoccupied molecular orbital (LUMO) levels were formed compared to monomers.