Designing an Efficient Singlet Fission Material with B−N Substitution in Pyrene: A Model Exact Study

Abstract

The electronic structure of boron (B)−nitrogen (N)-substituted pyrene molecules is the center of attraction in designing an efficient intermolecular singlet fission (x-SF) material. Thermodynamic energy criteria required for x-SF are obtained by captodative substitution with B and N in pristine pyrene to increase the lowest singlet−triplet energy gap. We computed lowlying excited states of BN-embedded pyrene molecules by exactly solving the Pariser−Parr−Pople (PPP) model Hamiltonian and compared these results with the TDDFT and EOM-CCSD values. Exact diagonalization of the PPP model Hamiltonian suggests that pristine pyrene, which is endothermic for x-SF, becomes isoergic with certain (BN) 2 substitution. The low-lying excited state energies calculated using the model Hamiltonian match very well with experimental values over EOM-CCSD and TDDFT. Moreover, the low value of the spin−orbit coupling constant calculated for BN-substituted pyrene strengthens its applicability as an SF material.