Solvent polarity effect on excited-state lifetime of carotenoids and some dyes.

The theory demonstrating the role of medium at the fluorescence quenching of polar compounds in solutions is briefly presented. It has been shown, that the rate of S(1) --> X(n) nonradiative conversion between the intramolecular charge transfer states depends on the permanent dipole moments in the ground (S(0)) and excited (S(1), X(n)) states as well as on solvent polarity. A relation for the rate of nonradiative excited-state energy conversion has been obtained and employed to test the known literature data for solvent effect on the S(1)-state lifetime of some biologically significant carotenoids and dyes (phthalimides). For phthalimides, the solvent isotope effect on the S(1)-state energy conversion, when hydrogen is replaced by deuterium in the OH groups of alcohols and water, has been analyzed. Based on the data for fluorescence quenching in solvents of different polarity, the dipole moments in the intermolecular charge transfer S(1) state have been obtained for carotenoids (peridinin, fucoxanthin, uriolide acetate) and for hydrogen-bonding complexes, which are formed by 4-amino-, 4-methylamino-, and 4-dimethylamino-N-methylphthalimides in alcohols and water.