EXCITED-STATE PROPERTIES OF QUINOXALINE-SUBSTITUTED PLATINUM 1,2-ENEDITHIOLATES

The complexes (dppe)M{S2C2(2-quinoxaline)(R)}, where dppe = (diphenylp hosphino)ethane, M = Ni, Pd, and Pt, and R = H and Me, have as their l owest-energy band an intraligand charge transfer transition (ILCT). Ex citation of deaerated solutions of (dppe)Pt{S2C2(2-quinoxaline)(R)} le ad to emissions from an (1)ILCT and an (3)ILCT*. The lifetimes of the se excited states (tau) and the quantum yields for the emissions (phi) for (dppe)Pt{S2C2(2-quinoxaline)(H)} in CH3CN are (1) tau = 0.16 ns, (1) phi = 0.005 and (3) tau = 3.3 mu s, (3) phi = 0.01, respectively. The (3)ILCT of these quinoxaline-substituted complexes can undergo a diverse suite of excited state reactions, including electron, proton, and hydrogen atom transfers. The second order rate constants (k(q)) fo r the quenching of the (3)ILCT emission by acids increases with the t hermodynamic driving force for the excited state proton transfer, an o bservation consistent with excited state electron and hydrogen atom tr ansfers. Dihydroquinone and p-methoxyphenol are substantially better q uenching agents than excited state proton transfer would predict and t hermodynamic calculations suggest that they quench the (3)ILCT by hyd rogen atom transfer.