Assessing Zethrene Derivatives as Singlet Fission Candidates Based on Multiple Descriptors

Singlet fission (SF) is a process where one singlet exciton splits into two triplet excitons. Utilizing SF may potentially increase the efficiency of solar cells beyond the Shockley–Queisser limit. To discover new SF materials, predictive descriptors for SF performance are needed. We consider multiple descriptors to assess several zethrene derivatives as candidate materials for intermolecular SF in the solid state. The descriptors include single molecule multiradical characters, many-body perturbation theory calculations of the thermodynamic driving force for SF and the singlet exciton charge transfer character in crystals, and a kinetic model based on molecular dimers extracted from the crystal structures. The zethrenes are compared to acenes known to exhibit SF with respect to these descriptors. The results indicate that all zethrene and heptazethrene derivatives studied here may exhibit SF. In particular, 7,14-bis(2,4,6-trimethylphenyl)dibenzo[ de, mn ]naphthacene (Z-T) emerges as a promising candidate. Its SF driving force is higher than tetracene, whose fission process is slightly endoergic, but lower than pentacene. Its singlet exciton charge transfer character is close to pentacene, and its crystal packing leads to a higher SF rate than other zethrene derivatives. Therefore, it may undergo fast SF with high energy efficiency. The approach of considering multiple descriptors may be useful for evaluating additional candidate materials for SF.