Searching for Diradicaloid Chromophores with Efficient Singlet Fission: Cyano‐Group Substitution of Difuropyrene Systems.

On the basis of theoretical models and calculations, CN‐substituted difuropyrene systems have been investigated as potential singlet fission (SF) candidates for solar cell applications. Calculations indicate that the fusion of difuran and pyrene in different arrangements could introduce variable diradical properties, and the fused compound ab‐trans‐DFP has moderate diradical character (y0=0.45) while satisfying the main condition (ΔE1) of SF. Furthermore, CN‐substituted ab‐trans‐DFP (substituted at distinct positions) is used to adjust the frontier molecular orbital energy level to satisfy the SF secondary condition (ΔE2). Interestingly, the position of the cyano substituents has almost no effect on the diradical character, which can be explained by the insensitivity of the ring aromaticity to the cyano position. Both time dependent density functional theory (TD‐DFT) and multi‐configurational self‐consistent field (MCSCF) results confirm that the 4‐ and 5‐position cyano‐substituted ab‐trans‐DFP derivatives can satisfy the two energy conditions and may become potential SF candidates. This work provides an effective strategy for the rational design of new suitable diradical SF candidates, and it is expected that more polycyclic aromatic hydrocarbons such as pyrene can achieve SF conditions by chemical modification, such as fusion or substitution, to adjust the diradical character and the vertical excitation energy. [ABSTRACT FROM AUTHOR]