EXCITED-STATE DECAY PROCESSES OF BINUCLEAR RHODIUM(I) ISOCYANIDE COMPLEXES

Emission lifetimes, quantum yields, and polarized excitation spectra o f Rh2b42+ and Rh2(TMB)42+ (b = 1,3-diisocyanopropane; TMB = 2,5-diisoc yano-2,5-dimethylhexane) have been determined. The singlet and triplet dsigma --> psigma(1,3A2u) excited states are luminescent with radiat ive rates of ca. 10(8) and 10(4) s-1, respectively, consistent with va lues obtained from Strickler-Berg calculations based on the correspond ing absorption bands. Both singlet and triplet upper excited states (d pi --> psigma and metal-to-metal charge transfer, E(u) symmetry) under go nonradiative decay primarily to 3A2u, bypassing 1A2u, and the branc hing ratios for decay through several intermediate states have been es timated. The temperature dependences of the lifetimes of the 1A2u and 3A2u states of Rh2(TMB)42+ are interpreted in terms of a model in whic h potential-surface crossings with the B-3(2u). (dsigma - d(x2-y2)) s tate facilitate nonradiative decay.