Quantum Chemical Insights Into Tunable Charge Transfer and Singlet–Triplet Splitting in TADF Emitters

ABSTRACT Thermally activated delayed fluorescence (TADF) materials hold the key to next‐generation optoelectronics by converting both singlet and triplet excitons into light via rapid reverse intersystem crossing (RISC). However, designing chromophores that simultaneously feature a small singlet‐triplet gap (Δ E ST ), strong charge‐transfer (CT) character, and high photoluminescence efficiency remains elusive, as conventional donor–acceptor scaffolds suffer from nonradiative losses. Here, we harness through‐space charge transfer (TSCT) architectures, which spatially separate donor and acceptor units to suppress vibrational quenching and boost RISC, to overcome this trade‐off. We pair an N ‐(4‐methylphenyl)‐1,8‐naphthalimide acceptor with a suite of heteroatom‐modified 9,9‐dimethyl‐9,10‐dihydroacridine donors (D–A), including a dual‐donor (D–A–D) analogue, and systematically tune electronic coupling and molecular rigidity. To evaluate the photophysical implications of these structural modifications, we performed quantum‐chemical analyses of ground and excited‐state parameters (S 1 , T 1 , Δ E ST , Δ E HL ), along with natural transition orbital and energy decomposition studies to probe the nature of electronic transitions. Spin‐orbit coupling constants and ISC/RISC rate estimates were calculated to assess the excited‐state mechanism, while electron‐hole correlation metrics quantified the extent of charge separation. Together, these descriptors offer a comprehensive understanding of how donor identity, spatial arrangement, and conjugation control TADF behavior.