Simple computational screening of potential singlet fission molecules

Abstract

Singlet fission (SF) is a particularly interesting process that can ultimately excite two electrons using a single photon and has strong potential for increasing the efficiency of photovoltaic devices (solar cells). One limitation of SF research is the relatively small number of known materials that undergo efficient SF. With this limitation in mind, we have used simple computational criteria (TD-DFT excitation energies) to screen various chromophores. Starting from known SF molecules (pentacene, tetracene, pyrene, isobenzofuran, among others), the influence of peripheral substituents was investigated. Depending on the starting molecule and the type of substitution (e.g., symmetric vs. asymmetric, electron donating vs. withdrawing), the influence of chemical modifications is often modest but sometimes large enough to significantly influence the energetics of SF. Specifically, we look at systematic trends of excitation energies among pentacene derivatives and calculated the energy change for SF to estimate the degree of spontaneity, compared to pentacene. The most significant changes are generally caused by substituent groups containing either nitrogen or oxygen, when they are placed opposite each other in the middle of the pentacene molecule. Of all other molecules tested in addition to pentacene and tetracene, only isobenzofuran derivatives were predicted to satisfy all required energetic conditions for efficient SF.