Determination of electronic couplings in the singlet fission process using a nonorthogonal configuration interaction approach

Singlet fission has been explored as an alternative mechanism to enhance the performance of solar cells. In this work, we use a nonorthogonal configuration interaction approach to study the singlet fission process in solid 2-methylene-2H-indene, an identified potential singlet fission molecule. Results of the electronic coupling calculations in pairs of molecules show that this molecule is suitable for the efficient formation of the 1TT state (≈40 meV). We report, for the first time, a comparison of the nonorthogonal configuration interaction approach with two other theoretical methodologies: restricted active space with two spin flips and the ab initio Frenkel–Davydov exciton model.