Singlet fission dynamics in organic compounds containing hetero-atom linkers*

Singlet Fission (SF) is a spin-allowed multichromophore process in which a singlet exciton reached optically undergoes internal conversion to a bound triplet-triplet spin biexciton, which may further dissociate into two free triplets, each of which may contribute to the photoconductivity of an organic solar cell. SF has been explored in a wide variety of organic compounds wherein seemingly slight differences between otherwise similar compounds can lead to vast differences in SF dynamics. This has practical applications for SF-based materials that may potentially be used in the design and production of next generation solar cells. In recent years, research has shifted from intermolecular (xSF) to intramolecular (iSF) compounds wherein the former systems are characterized by through-space charge transfer contrasted with the through-bond dynamics that describe the latter. Many iSF compounds under active investigation are dimers of tetracene or pentacene in which the chromophores are connected by one of various types of linkers. Having investigated the sensitive dependence on connectivity in systems in which the linking monomer is itself an acene, we now present many-body calculations on the low-lying electronic states of iSF systems containing linkers characterized by multiple atomic species. With differning numbers of pi electrons from atoms in the unit as well as alternative conjugation patterns, these systems present a variety of features that have strong affects on SF dynamics and present novel opportunities for exploration of the relevant many-body wavefunctions and potential design of new SF-based solar cells.