Lifetime studies on the phosphorescence of the tetrahedral tetrahalomanganate ion in fused salts and solids

The phosphorescence of tetrabutylammonium tetrahalomanganate salts has been investigated, both in the crystal and in the fused salt. The lifetime behavior of the ⁴T₁ → ⁶A transition in these tetrahedral systems is extremely unusual: The phosphorescence remains in the low viscosity melt; the bromide lifetime is ten times smaller than the chloride at room temperature, but about twenty times larger at 130°C; there is highly specific structure in the lifetime data of the solid which correlates with thermal phase transitions. Dilution experiments demonstrate that cooperative effects and electronic charge transfer processes are not important in these species. An explanation is suggested in terms of both low Franck-Condon factors and of frequency or Stokes shift of accepting modes for vibronically-induced radiative decay by the steric packing effects of the neighboring organic ion. Experiments for distinguishing the effects of these two mechanisms are suggested.