Diphenoquinone as a Prototype of Singlet Fission Chromophores

Singlet fission (SF) is attracting attention due to its potential applications in organic photovoltaics, quantum computing, and dynamic nuclear polarization. In this article, we have theoretically investigated the potential of 4,4'-diphenoquinone (<b>1a</b>) as a promising backbone for efficient SF chromophores. Single-reference <i>ab initio</i> correlated methods were employed to investigate the excited states of <b>1a</b>. A strong photoabsorption is predicted for the S₀-S₃ transition, which is described by HOMO-LUMO excitation. Although the excitation energies of S₃ and T₁ states satisfy the exothermic energy matching condition of SF, internal conversion from the S₃ to a low-lying nπ* singlet excited state may suppress the efficient generation of ¹(T₁T₁) in the condensed phase. We have demonstrated that the obstacle of <b>1a</b> can be overcome by introducing typical donors or halogen atoms and fusing aromatic six-membered ring(s) while retaining the advantages of the diphenoquinone backbone.