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 CH3-CN 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 PtII complex absorption, a maximum at similar to 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.