SPECTRAL, LIFETIME AND PHOTOCHEMICAL CHARACTERISTICS OF 4-ACETOXY-CHALCONE IN VISCOUS MEDIA

Both fluorescence and excitation spectra of 4-acetoxy-chalcone (4-AC) are bathochromically shifted as the medium polarity increases. The flu orescence quantum yields are sensitive to medium viscosity and increas e sharply as the medium viscosity increases due to prohibition of radi ationless deactivation pathways. The fluorescence lifetime of 4-AC in glycerol has been measured as tau = 1.9 ns. The photochemical quantum yields (thought to be a trans-cis photo-isomerization) are also sensit ive to medium viscosity with minimum phi(c) values obtained in highly viscous solvents. The effect of medium viscosity on the quenching of 4 -AC fluorescence using picric acid as a quencher has been studied. A s tatic-type quenching mechanism is proposed to account for the quenchin g efficiency as the medium viscosity increases.