Photoinduced electron transfer between [Cu(dmphen)L(2)](+) [dmphen=2,9-dimethyl-1,10-phenanthroline, L=PPh(n)(C(6)H(4)OMe-p)(3-n) (n=0-3)] and methyl viologen

Photocatalytic reduction of methyl viologen (1,1'-dimethyl-4,4'-bipyridinium mv(2+)) was efficiently carried out with copper(I) complexes [Cu(dmphen)L(2)](+) [dmphen = 2,9-diinethyl-1,10-phenanthroline, L = PPh(n)(C(6)H(4)OMe-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, phi(mv(.+)), increases considerably in the order L = PPh(3) much less than PPh(2)(C(6)H(4)OMe-p) PPh(C(6)H(4)OMe-p)(2) < P(C(6)H(4)OMe-p), i.e. in increasing order of the phosphine donation ability. The best quantum yield (0.1) was recorded when [Cu(dmphen){P(C(6)H(4)OMe-p)(3)}(2)](+) was used. Kinetic analysis and measurement of the lifetime of the excited copper(I) complex revealed the reason why phi(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.