Competitive radiative decay and metal-metal bond cleavage from the lowest excited state of triphenyltin- and triphenylgermanium tricarbonyl(1,10-phenanthroline)rhenium

Abstract : The complexes Ph3ERe(CO)3( ,10-phenanthroline) (E = Sn, Ge) exhibit optical emission (approx. 750 nm) from the lowest excited state in CH2Cl2/CCl4 solutions at 298deg. K and also give E-Re bond cleavage (Phi approx. 0.25) upon photoexcitation under the same conditions. Both the relative emission quantum yield and the reaction quantum yield for ClRe(CO)3 (l,10-phenanthroline) formation are independent of excitation wavelength consistent with reaction and emission originating from the lowest excited state. The emission is now quenched by CCl4 in benzene solution, ruling out excited state, bimolecular, electron transfer to CCl4 as the reaction mechanism. Rather, the mechanism is likely slow (approx. 1/100000 sec) E-Re dissociation. This notion is in accord with a lowest excited state.