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

Emission lifetimes, quantum yields, and polarized excitation spectra of Rh2b42+ and Rh2(TMB)42+ (b = 1,3-diisocyanopropane; TMB = 2,5-diisocyano-2,5-dimethylhexane) have been determined. The singlet and triplet dsigma* --> psigma(1,3A2u) excited states are luminescent with radiative rates of ca. 10(8) and 10(4) s-1, respectively, consistent with values obtained from Strickler-Berg calculations based on the corresponding absorption bands. Both singlet and triplet upper excited states (dpi --> psigma and metal-to-metal charge transfer, E(u) symmetry) undergo nonradiative decay primarily to 3A2u, bypassing 1A2u, and the branching ratios for decay through several intermediate states have been estimated. The temperature dependences of the lifetimes of the 1A2u and 3A2u states of Rh2(TMB)42+ are interpreted in terms of a model in which potential-surface crossings with the B-3(2u). (dsigma* - d(x2-y2)) state facilitate nonradiative decay.