PHOTOCHEMISTRY OF RU(BPY)(2)(DCBPY)(2+) ON AL2O3 AND TIO2 SURFACES - AN INSIGHT INTO THE MECHANISM OF PHOTOSENSITIZATION

Diffuse reflectance studies have been undertaken to investigate the photochemical behavior of a ruthenium complex, bis(2,2'-bipyridine) (4,4'-dicarboxy-2, 2'-bipyridine)ruthenium(II) [Ru(bpy)(2)(dcbpy)(2+)], on the surface of Al2O3 and TiO2 particles. Decreased emission yield and lifetime of excited Ru(bpy)(2)(dcbpy)(2+) on TiO2 surface indicated dominance of the charge injection process in deactivating excited sensitizer. The rate constant for the heterogeneous electron transfer rate constant as measured from the analysis of luminescence decay was in the range (1.0-5.5) x 10(8) s(-1). Upon irradiation with visible light, the degassed sample of Ru(bpy)(2)(dcbpy)(2+)-coated TiO2 particles turned blue as photogenerated electrons got trapped at the TiO2 surface. The blue color disappeared instantly upon exposure to air. Irreversible degradation of the sensitizer was noticeable when air-equilibrated samples were photolyzed with visible light for an extended period. Diffuse reflectance FTIR studies confirmed the semiconductor surface assisted photodegradation of Ru(bpy)(2)(dcbpy)(2+).