Photoinduced electron transfer between [Cu(dmphen)L2]+[dmphen = 2,9-dimethyl-1,10-phenanthroline, L = PPhn(C6H4OMe-p)3 –n(n= 0–3)] and methyl viologen

Abstract

Photocatalytic reduction of methyl viologen (1,1′-dimethyl-4,4′-bipyridinium mv²⁺) was efficiently carried out with copper(I) complexes [Cu(dmphen)L₂]⁺[dmphen = 2,9-dimethyl-1,10-phenanthroline, L = PPh_n(C₆H₄OMe-p)_{3 –n}, n= 0–3] upon irradiation of the metal-o-ligand charge-transfer band at around 360 nm. The quantum yield for reduction, φ(mv˙⁺), increases considerably in the order L = PPh₃ PPh₂-(C₆H₄OMe-p) < PPh(C₆H₄OMe-p)₂ < P(C₆H₄OMe-p)₃, i.e. in increasing order of the phosphine donation ability. The best quantum yield (0.1) was recorded when [Cu(dmphen){P(C₆H₄OMe-p)₃}₂]⁺ was used. Kinetic analysis and measurement of the lifetime of the excited copper(I) complex revealed the reason why φ(mv˙⁺) increases as the phosphine donation ability increases: first, the excited state becomes longer-lived and secondly, the charge-separation step becomes easier with increasing donation ability. The significant phosphine effects on the excited-state lifetime are discussed in terms of the solvent interaction with the copper(I) centre.