| Abstract | Photophysical and photochemical properties for 4,6-diphenyl-3-cyanopyridin-2(1H) thione (CPPT) and 4-phenyl-6-toly-3-cyanopyridin-
2(1H)-thione (CMPT) have been investigated by various spectroscopic methods including transient absorption.With changing the solvent
polarity, CPPT andCMPTexhibited the thione-thiol tautomeric equilibria. Laser flash photolysis studies in polar solvents and protic solvents
have revealed that triplet state formation was predominantly observed by the thione tautomer, which was supported by the characteristic
self-quenching in the rate constants of .2:99–5:68/ 109 dm3 mol?1. In nonopolar and less polar solvents, on the other hand, the thio
radical was observed by photoinduced homolytic S–H bond cleavage of the thiol form. Absorption and fluorescence spectra indicate the
considerable shifts with the solvent polarity in each form in addition to the equilibria. From the fluorescence lifetimes, the tautomeric forms
can also be discriminated. © 2000 Elsevier Science B.V. All rights reserved. |