Data-Driven and Quantum-Chemical Insights into Emergence of Multiresonance Effect in Thermally Activated Delayed Fluorescence Emitters

Abstract

Multiresonance thermally activated delayed fluorescence (MR-TADF) emitters enable narrow-bandwidth emission and high efficiency in organic light-emitting diodes; however, the fundamental origin of the multiresonance effect remains incompletely understood. Herein, a fine-tuned Uni-Mol model trained on reported MR-TADF emitters identifies BN-embedded aromatic units as the primary structural motif governing small singlet–triplet energy gaps. Wave function-based quantum chemical calculations subsequently validate this prediction and provide a mechanistic understanding of the underlying electronic structure. While the minimal BN-containing unit dictates the singlet–triplet splitting, π-extension primarily controls vibronic stabilization and emission bandwidth. The multiresonance effect is shown to arise from a cooperative interplay of phase-separated orbital topology, suppressed exchange interactions and enhanced excited-state correlation, further reinforced by heteroatom-induced electronic polarization that yields nearly identical S1 and T1 charge distributions. Combined with the data-driven identification of boron positioning as the dominant modulator of singlet–triplet splitting and nitrogen−π coupling as a key determinant of emission color, this work provides actionable design principles for next-generation MR-TADF emitters with controlled spectral purity and near-zero singlet–triplet gaps.