Tetracene Aggregation on Polar and Nonpolar Surfaces: Implications for Singlet Fission

In molecular crystals that exhibit singlet fission, quantum yields depend strongly on intermolecular configurations that control the relevant electronic couplings. Here, we explore how noncovalent interactions between molecules and surfaces stabilize intermolecular structures with strong singlet fission couplings. Using molecular dynamics simulations, we studied the aggregation patterns of tetracene molecules on a solid surface as a function of surface polarity. Even at low surface concentrations, tetracene self-assembled into nanocrystallites where about 10-20% of the clustered molecules were part of at least one herringbone structure. The herringbone structure is the native structure of crystalline tetracene, which exhibits a high singlet fission quantum yield. Increasing the polarity of the surface reduced both the amount of clustering and the relative number of herringbone configurations, but only when the dipoles on the surface were orientationally disordered. These results have implications for the application of singlet fission in dye-sensitized solar cells.