Primary photophysical properties of 4H-1-benzopyran-4-thione in cyclodextrin complexes

Abstract

The influence of cyclodextrins (CDs) on the photophysics of 4H-1-benzopyran-4-thione (BPT) has been studied in solution and in the solid state by steady-state absorption, emission and circular dichroism as well as by time-resolved diffuse reflectance laser flash photolysis. The spectral changes and induced circular dichroism indicate the formation of the cyclodextrin complexes of BPT. The very low fluorescence quantum yield from the S ₂ state for this complex, similar to that measured for BPT alone in water, suggests that there is an interaction between water and guest molecules in the CD complexes leading to shortening of the S ₂ state lifetime. The Albery model was used to analyse the phosphorescence of the BPT·β-CD solid complex. The values obtained for the average rate constants, , are similar to values of the triplet state decay constant of the thioketone in inert solvents at infinite dilution, k ₀ . Quenching by oxygen does not play an important role when thioketones are included within cyclodextrins in the solid state.