Photoinduced Electron-Transfer Reactions of Platinum(II) Terpyridyl Acetylide Complexes: Reductive Quenching in a Hydrogen-Generating System

The one-electron reduction of [(mpt)Pt(CCPhCl)] ClO4 [mpt = 4'-(4-methylphenyl)-2,2',6',2' '-terpyridyl; CCPhCl = chlorophenyl acetylide] by a series of amine donors was investigated in a CH3CN solution. The excited state has a lifetime of 550 ns in the absence of quencher in degassed CH3CN. Quenching rate constants were >10(8) M(-1) s(-1) even for trialkylamines. Transient absorption spectroscopy provided convincing evidence for the production of the one-electron-reduced Pt complex, even with quenchers that could potentially serve as H-atom donors. The transient spectrum obtained in the presence of triethylamine exhibits, in addition to bleaching of the Pt(II) complex absorption, a maximum at approximately 360 nm and broad absorption from 500 to 800 nm, indicating that the reduced complex has a complex electronic structure and is not easily assigned as a terpyridyl anion radical.