Solvent and substituent effects on the photoreduction of cobalt(III)-aryl amine complexes in an aquo-organic solvent medium

The photoreduction of a series of Co-III complex ions, [Coen(2)Cl(RC6H4NH2)](2+) where R = p-OMe, p-OEt, p-Me, m-Me, H, and p-F, has been studied using a low pressure Hg vapour lamp as the light source (254 nm) in an aquo-organic solvent [15-40% (v/v) 2-methylpropan-2-ol] medium. Quantum yields for Co-II production by redox decomposition have been determined in all cases. The quantum yield increases considerably with the increase in concentration of the organic co-solvent in the binary solvent mixture under investigation. The Hammett correlation is linear, affording negative reaction constants, which indicate that the excited state is electron deficient. Correlation of the experimental results with Kamlet-Taft's solvatochromic parameters indicates that the solvent hydrogen bond donor acidity plays a dominant role in governing the reactivity.