PHOTOPHYSICS OF AROMATIC THIOKETONES SUPPORTED ON CELLULOSE

The photophysical and spectroscopic properties of four thioketones, 4H -1-benzopyran-4-thione, xanthione, thioflavone and Michler's thione, a bsorbed on cellulose have been measured and have been compared with th e properties of the same compounds in homogeneous solutions of varying polarities and in beta-cyclodextrin (beta-CD) inclusion complexes. Th e phosphorescence spectra, solvent shifts and triplet lifetimes all su ggest that the thioketones are bound at polar sites on cellulose, and that the lowest triplets are of pi,pi character. Analysis of the trip let state decays using dispersion kinetics reveals that the thioketone s exhibit a wider distribution of decay constants on cellulose than in beta-CD as a consequence of their larger number of possible orientati ons and binding locations on the open-chain polysaccharide.