Davydov Splitting and Band Structure for Triplet Excitons in Pyrene

The first peak (0-0 transition) of the singlet-triplet delayed fluorescence excitation spectrum in pyrene has been investigated in polarized light. The $b$-polarized transition is found to be at higher energy than the $a$-polarized transition by a Davydov splitting of 2.4 ± 0.6 ${\mathrm{cm}}^{-1\mathrm{}}$. An expression for the energy bands $\epsilon \left(\overrightarrow{\mathrm{k}}\right)$ is derived and related to the Davydov splitting. Transport properties of the triplet excitons have been evaluated and indicate that the diffusion of triplet excitons in pyrene is due more to a hopping process than to coherent band motion.