Photophysics of aromatic thioketones supported on cellulose

Abstract

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