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

Diffuse reflectance studies have been undertaken to investigate the ph otochemical 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 d ominance of the charge injection process in deactivating excited sensi tizer. The rate constant for the heterogeneous electron transfer rate constant as measured from the analysis of luminescence decay was in th e 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 tur ned blue as photogenerated electrons got trapped at the TiO2 surface. The blue color disappeared instantly upon exposure to air. Irreversibl e degradation of the sensitizer was noticeable when air-equilibrated s amples were photolyzed with visible light for an extended period. Diff use reflectance FTIR studies confirmed the semiconductor surface assis ted photodegradation of Ru(bpy)(2)(dcbpy)(2+).