Picosecond time-resolved S2→S0 fluorescence of xanthione in different fluid solvents

Abstract

Time-correlated single-photon counting experiments at ≈ 25 ps resolution have been used to measure the S2 fluorescence decay time of xanthione in different fluid solvents. Systematic differences in S2 lifetime in the range 20–30 ps are revealed for a homologous series of n-alkane solvents, and an increase in lifetime for extensive chain branching is also noted. Solutions of xanthione in aromatic solvents and in alcohols are found to exhibit fluorescence decay limes < 20 ps. Little evidence is seen which would support a nonradiative relaxation mechanism involving Franck-Condon selective energy transfer to high-energy vibrational modes of the solvent. Instead, the current results provide support for a mechanism in which a reversible solvent-solute chemical reaction, probably involving bond insertion, is responsible for the solvent dependence of the S2 fluorescence decay time.