Photophysical and photochemical properties of 1,2,4-trihydroxy-9,10-anthraquinone adsorbed on inorganic oxides.

The photophysical and photochemical properties of 1,2,4-trihydroxy-9,10-anthraquinone (purpurin) adsorbed on three inorganic oxides (SiO2, Al2O3 and TiO2) were compared with those shown by the same molecule in solution and in solid phase. In particular, steady-state (absorption and fluorescence) and transient (laser flash photolysis) techniques were used to characterize the lowest excited singlet and triplet states together with the transients (ketyl radicals and cation radicals) formed through the primary decay processes of the excited states of purpurin both in solution and adsorbed on the oxide surfaces. TiO2 is particularly efficient to sensitize the oxidation of purpurin and to form colourless photoproducts, while purpurin absorbed on SiO2 and Al2O3 is much more stable. This is related to the ability of the solid matrix to induce the formation of the purpurin cation radical and to direct its decay towards reactive channels.