Highly Efficient Full-Color Thermally Activated Delayed Fluorescence Materials Based on Quinolino-acridine: Theoretical Molecular Study and Design

Abstract

In this study, we systematically investigated six donor-acceptor (D-A) type TADF molecules featuring a qunolino-acridine donor moiety to screen highly efficient full-color TADF materials and reveal the effect of A fragment on the radiative and RISC processes. Our results suggest that precise modulation of D-A interactions enables control of excited-state characteristics, yielding small singlet-triplet energy gaps (ΔEST = 0.035‒0.074 eV) through optimal spatial separation of HOMO and LUMO orbitals. All molecules exhibit strong charge transfer (CT) character in S1 states while either CT-dominant or hybrid CT/local excitation (LE) character in T1 states, which brings in strong spin‒orbital coupling, further resulting in exceptional RISC rates (106‒107 s‒1). Radiative decay rates (kr) 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 rational selection of A units, demonstrating the versatility of qunolino-acridine-based systems. We hope these findings establish a robust theoretical framework for developing qunolino-acridine-based TADF materials with optimized performance for OLED applications.