Excited-state decay processes of binuclear rhodium(I) isocyanide complexes

Abstract

Emission lifetimes, quantum yields, and polarized excitation spectra of Rh_2b_4^(2+) and Rh_2(TMB)_4^(2+) (b = 1,3-diisocyanopropane; TMB = 2,5-diisocyano-2,5-dimethylhexane) have been determined. The singlet and triplet dσ* → pσ(^(1,3)A_(2u) excited states are luminescent with radiative rates of ca. 10^8 and 10^ s^(-1), respectively, consistent with values obtained from Strickler-Berg calculations based on the corresponding absorption bands. Both singlet and triplet upper excited states (dπ → pσ and metal-to-metal charge transfer, E_u symmetry) undergo nonradiative decay primarily to ^3A_(2u), bypassing ^1A_(2u), and the branching ratios for decay through several intermediate states have been estimated. The temperature dependences of the lifetimes of the ^1A_(2u), and ^3A_(2u) states of Rh_2(TMB)_4^(2+) are interpreted in terms of a model in which potential-surface crossings with the ^3B_(2u) (dσ* - d_(x^2 - y^2)) state facilitate nonradiative decay.

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