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Photophysical and photochemical properties of rhodium(III) halopentaammine complexes in aqueous solution. Reaction kinetics of ligand field excited states


Reported are the photoluminescence spectra, lifetimes and quantum yields, and ligand photosubstitution reaction quantum yields for the rhodium(III) complexes Rh(NH3)5Cl2+ and Rh(NH3)5Br2+ and their perdeuterated analogues in ambient temperature aqueous solution. When combined with the conclusions based on earlier sensitization studies that intersystem crossing/internal conversion to the lowest energy ligand field states occurs with approximately unitary efficiency, these results allow calculation for the first time of the individual rate constants for the radiative, nonradiative, and reactive deactivation pathways from these excited states for a d6 complex under photochemically relevant conditions. The perdeuterio complexes demonstrated higher quantum yields for both photosubstitution and photoemission than their perprotio analogues, a result which can be attributed to reduction of the nonradiative deactivation rate constants in the former cases. The correspondence between deuteration effects on excited-state lifetimes and on photoreaction quantum yields indicates that chemical reaction is directly competitive with the other deactivation pathways of the ligand field excited state. Lastly, comparison of the excited state ligand substitution rate constants with those of analogous thermal reactions indicates the excited state reactions to be the faster by 14-15 orders of magnitude. © 1979, American Chemical Society. All rights reserved.

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