Molecular Design of Pyromellitic Diimides for Triplet‐Driven Photocatalysis: Computational Insights

ABSTRACT

Organic photocatalysts (OPCs) offer highly promising, metal‐free alternatives to conventional photocatalysts, enabling organic transformations under mild conditions. Achieving balanced oxidation and reduction capabilities in the triplet excited state remains a formidable challenge, as strengthening one often compromises the other. Herein, we present the rational design and comprehensive computational characterization of a series of pyromellitic diimide (PmDI)‐ and its angled isomer, mellophanic diimide (MDI)‐based donor‐acceptor OPCs. Employing DFT and TD‐DFT at the PBE0/6‐31+G** level in dichloromethane, we systematically evaluated geometrical, electronic, excited‐state properties, ground‐state and excited‐state redox potentials across various PmDI units modified with ten diverse donor substituents at core and terminal positions. This approach elucidates how donor strength and substitution regiochemistry finely tune photophysical and redox properties. Remarkably, most designed OPCs exhibit well‐balanced triplet‐state redox potentials, rendering them versatile for diverse photoredox reactions. Select derivatives display exceptionally strong and balanced excited‐state potentials‐reaching down to −2.10 V and up to +2.51 V (vs SCE) in the triplet state. These properties position the PmDI‐based OPCs as a potential candidate for demanding triplet‐state‐driven photocatalysis. This study establishes robust structure‐property guidelines for engineering next‐generation metal‐free photocatalysts with precisely tunable redox behaviour.