Highly efficient full-color thermally activated delayed fluorescence materials based on quinolino-acridine: theoretical molecular study and design

In this study, six donor-acceptor (D-A)-type TADF molecules featuring a quinolino-acridine donor moiety were systematically investigated to obtain highly efficient full-color TADF materials and reveal the effect of the A fragment on the radiative and RISC processes. The results suggest that precise modulation of D-A interactions enables control of the excited-state characteristics, yielding small energy gaps between S₁ and T₁ (Δ<i>E</i>_ST = 0.035-0.074 eV) through optimal spatial separation of the HOMO and LUMO orbitals. All molecules exhibit strong charge transfer (CT) character in S₁ states and either CT-dominant or hybrid CT/local excitation (LE) character in T₁ states, which results in strong spin-orbital coupling, further resulting in exceptional RISC rates (10⁶-10⁷ s^-1). The radiative decay rates (<i>k</i>_r) of these molecules remain sufficiently large for efficient fluorescence, while nonradiative pathways are primarily governed by S₁/S₀ structural relaxation and vibronic coupling between electronic and vibrational transitions. Notably, our molecular design strategy successfully achieves full-color emission tuning through the rational selection of A units, demonstrating the versatility of quinolino-acridine-based systems. We hope these findings establish a robust theoretical framework for developing quinolino-acridine-based TADF materials with optimized performance for OLED applications.