PHOTOINDUCED ELECTRON-TRANSFER BETWEEN [CU(DMPHEN)L(2)](-DIMETHYL-1,10-PHENANTHROLINE, L=PPH(N)(C(6)H(4)OME-P)(3-N) (N=0-3)] AND METHYL VIOLOGEN() [DMPHEN=2,9)

Photocatalytic reduction of methyl viologen (1,1'-dimethyl-4,4'-bipyri dinium mv(2+)) was efficiently carried out with copper(I) complexes [C u(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-liga nd charge-transfer band at around 360 nm. The quantum yield for reduct ion, 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 be st 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(.+)) i ncreases as the phosphine donation ability increases: first, the excit ed state becomes longer-lived and secondly, the charge-separation step becomes easier with increasing donation ability. The significant phos phine effects on the excited-state lifetime are discussed in terms of the solvent interaction with the copper(I) centre.