Unleashing Ambient Triplet Harvesting Pathways in Arylene Diimides via Modular, Noncovalent Charge Transfer Interactions

Development of organic molecules that can harvest triplet excitons under ambient conditions by a relatively simple strategy holds great promise in the paradigm of photophysics. Deploying through-space charge transfer (CT) interactions via noncovalently stacked donor–acceptor molecular design that can be tuned in accordance with simple structural modifications can be considered an attractive strategy toward this direction. Herein, we accomplish a precise control in tuning the triplet harvesting pathways in donor–acceptor cocrystals by engineering CT complexation between them. We use pyromellitic diimide (PmDI) phosphor to cocrystallize with different donors such as dibenzofuran (DBF), dibenzothiophene (DBT), and dibenzoselenophene (DBS) that augment CT complexation between the two counterparts and carefully toggle the emission into singlet CT (1CT) fluorescence, thermally activated delayed fluorescence (TADF), and triplet CT (3CT) phosphorescence, in their respective cocrystals. On moving from PmDI-DBF to PmDI-DBT, emission was biased from 1CT fluorescence to TADF. The synergistic involvement of the strong heavy-atom effect with CT complexation diverts the excited emission from TADF to exclusively 3CT phosphorescence in PmDI-DBS. Most crucially, we not only put forward a methodology for biasing the excited state to various ambient triplet harvesting pathways but also glorify a modular noncovalent donor–acceptor strategy without complicated synthetic efforts unlike conventional covalent donor–acceptor molecular designs.