PRIMARY PHOTOPHYSICAL PROPERTIES OF 4H-1-BENZOPYRAN-4-THIONE IN CYCLODEXTRIN COMPLEXES

The influence of cyclodextrins (CDs) on the photophysics of 4H-1-benzo pyran-4-thione (BPT) has been studied in solution and in the solid sta te by steady-state absorption, emission and circular dichroism as well as by time-resolved diffuse reflectance laser hash photolysis. The sp ectral changes and induced circular dichroism indicate the formation o f the cyclodextrin complexes of BPT. The very low fluorescence quantum yield from the S-2 state for this complex, similar to that measured f or BPT alone in water, suggests that there is an interaction between w ater and guest molecules in the CD complexes leading to shortening of the S-2 state lifetime. The Albery model was used to analyse the phosp horescence of the BPT . beta-CD solid complex. The values obtained for the average rate constants, (k) over bar are similar to values of the triplet state decay constant of the thioketone in inert solvents at i nfinite dilution, k(o). Quenching by oxygen does not play an important role when thioketones are included within cyclodextrins in the solid state.