Photoinduced electron transfer between [Cu(dmphen)L₂]⁺[dmphen = 2,9-dimethyl-1,10-phenanthroline, L = PPh_n(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 = PPhn(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.