Topochemically photoreacted fluorescent dimers of 2,3-dicyanopyrazines

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 1H 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 π-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.

► Synthesis 2,3-Dicyanopyrazines dimers by [2+2] photocycloaddition.
► Cyclobutane ring dimer which induce hypsochromic shift and increasing fluorescence intensity.
► Spin-coated thin film for negative photoresist application.