Phenylated Acene Derivatives as Candidates for Intermolecular Singlet Fission

Singlet fission (SF), the conversion of one singlet exciton into two triplet excitons, may improve the efficiency of organic photovoltaics. Only a few materials have been experimentally observed to undergo intermolecular SF, most of which are acenes and their derivatives. Using many-body perturbation theory in the GW approximation and the Bethe-Salpeter equation (BSE), we systematically investigate the electronic and excitonic properties of tetracene, pentacene, and their phenylated derivatives in the gas phase and solid state. Their potential for SF is evaluated with respect to the thermodynamic driving force and the singlet exciton charge transfer character. In both gas phase and solid state, pentacene and its derivatives are more promising than tetracene and its derivatives. Within a group of phenylated derivatives with the same acene backbone, increasing the number of phenyl side groups is detrimental for SF in the gas phase. However, solid state properties are additionally affected by intermolecular interactions. We find that a higher number of phenyl side groups results in crystal structures with weak π-stacking and slip stacking, which exhibit higher SF driving force in the solid state.