Fluorescence quenching of the ketocyanine dyes in polar solvents: anti-TICT behavior

Spectral properties and fluorescence decay in a series of differently N-substituted ketocyanine dyes belonging to the dibenzalcyclopentanone type were studied 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 S-1 and S-0 states in polar solvents. The alternative model of non-luminescent TICT states formation was shown to be less probable in the discussed series. (C) 2003 Elsevier Science B.V. All rights reserved.