Systematic Engineering of Acceptor Substituents in Blue TADF Emitters for Optimized Excited-State Dynamics and OLED...

Thermally activated delayed fluorescence (TADF) materials enable nearly 100% internal quantum efficiency in OLEDs, yet the substituent-dependent regulation of excited states in boron-based acceptors remains insufficiently clarified. In this study, we theoretically investigate the blue boron-based TADF emitter BOBT and five of its derivatives (B1-B5) bearing electron-withdrawing groups (-F, -Cl, -CN, -COOH, -COOCH3), to clarify how acceptor engineering influences charge transfer, singlet-triplet separation, and exciton-conversion dynamics. The analysis shows that systematic substitution effectively tunes donor-acceptor decoupling, frontier orbital gaps, ΔE _ST, and oscillator strengths. Among the substituted derivatives, B5 presents the most balanced excited-state profile, combining a reduced bandgap, a relatively small ΔE _ST of 0.106 eV, and appreciable S₁-T₁/T₂ spin-orbit coupling. These results indicate that targeted acceptor engineering can effectively regulate excited-state energetics and spin mixing in blue TADF materials, although the present calculations do not allow a definitive conclusion that the RISC rate is enhanced relative to the parent molecule B.