Photoreactivity differences of [CrIII(N–N)3]3+ and [CrIII(N–N)2RCl]2+ complex ions in aquo-methanol/1,4-dioxane binary mixtures

Photoaquation of [CrIII(N–N)3]3+ ((N–N) = en, pn and tn) and [CrIII(N–N)2RCl]2+ (R = C6H5NH2, o-MeC6H4NH2 and p-MeC6H4NH2) complexes in water/methanol (MeOH) and water/1,4-dioxane (Diox) binary solutions (composition: water/methanol (1,4-dioxane) are 20/0, 19/1, 18/2, 17/3,16/4, 15/5, 14/6, v/v) have been followed and quantum yields were estimated. The measured photoefficiencies vary linearly with molefraction, x2, of cosolvent and Φ is found to either increase or decrease. It is determined to attain an upper limit regularly or a lower limit as the x2: xMeOH/xDiox of the medium is increased from 0.0229/0.019 to 0.1602/0.0831. The nature of solvation has notable effects on Φ describing a logarithmic relationship to between quantum yield and empirical solvent scales like ɛr, Y, ETN, DNN, α, β and π*. A correlation equation of the form Y S = Y 0 + ∑ n = 1 ∞ a i X i is useful in understanding the role of solvent in terms of both qualitative and quantitative manner. The unprecedented change in quantum yield and the influence of solvent as a mediating agent are discussed.