New fluorescent dye of dibenzalcyclopentanone series possessing increased solvatochromism and “energy gap law” regulated fluorescence quenching in polar solvents

New ketocyanine dye of dibenzalcyclopentanone series, characterized by the increased solvatochromism, was synthesized. Its spectral behavior was examined in solvents of various polarity and hydrogen bonding ability. The significant solvent-induced fluorescence quenching was explained by the increase of internal conversion rate owing to the lowering of the energy gap between S1 and S0 states in polar solvents, instead of the alternative scheme with the possible formation of non-fluorescent TICT states.