Deuterium Isotope Effect in the Photophysics of Chromium (III) Alkylamine Complexes

Abstract
The photophysical properties of a series of chromium alkylamines with CrN6 skeletons were studied in a mixture of dimethylsulfoxide (DMSO) and water (1:1 vv). For the analogous N‐deuterated compounds DMSO/D2O (1:1 vv) was used as the solvent Absorption spectra, phosphorescence quantum yields, and phosphorescence decay times were measured. At low temperatures the protonated complexes were found to decay mainly nonradiatively with NH stretching modes accepting the excitation energy. In the deuterated species the radiative decay became important. Phosphorescence quantum yields as high as 0.42 were obtained. ND stretching modes did not significantly contribute to the nonradiative deactivation in agreement with Kupka's theory. At higher temperatures (250–295 K) a smaller isotope effect was observed. The apparent activation energies of the high temperature decay increased on deuteration.

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