Low-temperature phosphorescence and triplet exciton transport in 4-bromobenzophenone polymorphs

Phosphorescence spectra of two 4-bromobenzophenone polymorphs have been measured at 1.6 K. Based on the actual structure data for the triclinic and monoclinic polymorphs, the relevant exciton dispersion laws have been calculated within a 1D model to show that the exciton band in the triclinic form should be appreciably wider than in the triclinic one. Comparative analysis of the shapes of the observed 0–0 phosphorescence bands at liquid-helium temperature provide evidence that the triplet exciton diffusion is more efficient in the triclinic form, which corroborates the conclusions of our simple theory.