Radiative and radiationless decay processes in rhodium(III) ammine complexes

Luminescence quantum yields and lifetimes of a series of rhodium(III) halopentammines have been determined at 110°K in water-methanol glasses. Deuterium substitution of the solute-solvent mixture is found to enhance the luminescence lifetimes significantly. The weak and strong coupling mechanisms for radiationless processes are compared, and it is concluded that these complexes are examples of the weak coupling mechanism in spite of the large Stokes shifts found in their emission spectra. The radiative lifetimes of the series of complexes are interpreted on the basis of a spin-orbit-coupling model for dd luminescence. The effect of perdeuteration on the luminescence lifetime of trans-dibromotetra(pyridine)rhodium(III) bromide is reported and compared with the effect of deuteration of the water-methanol solvent system. A large enhancement of the luminescence lifetime is observed in both cases.