Abstract Thermally activated delayed fluorescence (TADF) has emerged as a sustainable alternative to phosphorescent organic light emitting diodes (OLEDs), offering 100% exciton utilization without the need for heavy metals. In this study, how donor and acceptor strength, as well as linkage topology, govern the photophysical behavior of a series of imidazopyridine‐based emitters using density functional theory (DFT) is explored. It is shown that strong electron donors reduce the singlet–triplet energy gap (Δ E ST ), enhance charge‐transfer (CT) character, and induce non‐negligible spin–orbit coupling (SOC)—leading to efficient reverse intersystem crossing (RISC). In contrast, weak donors yield larger Δ E ST , higher reorganization energies, and significantly slower RISC rates. Meta‐linked isomers consistently outperform ortho and para ‐analogues in terms of RISC efficiency due to their balanced Δ E ST –SOC interplay. Cyano‐substitution on the acceptor core further tunes electronic properties by enhancing the electron‐withdrawing nature, particularly in ortho configurations. Detailed DUSHIN analyses uncover how rotational and vibrational modes modulate reorganization energies and impact triplet harvesting dynamics. Notably, weak‐donor derivatives exhibit room‐temperature phosphorescence (RTP) with phosphorescence rate constants ( k p ) ranging from 1 to 10 3 s −1 . These results provide comprehensive design guidelines for the next generation of imidazopyridine‐based TADF and RTP emitters in OLED applications.
Panaha et al. (Thu,) studied this question.
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