Overcoming the Spin-Orbit Coupling Limitation: Cooperative Singlet-Triplet Energy Gap and Reorganization Energy Engineering for High-Efficiency Thermally Activated Delayed Fluorescence in Carbene-Cu(I)-Amide Systems

Abstract

This study systematically investigated the structure-property relationship of Cu(I) carbene-metal-amide (CMA) complexes using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Potential energy surface analysis revealed that planar geometry represents the most stable configuration for both ground and excited states. By modulating ligand structures, we not only elucidated the luminescence mechanism in solution phase but also demonstrated that the synergistic effect of small singlet-triplet energy gap (ΔE_ST) and low reorganization energy (λ) can facilitate rapid reverse intersystem crossing (RISC) despite weak spin-orbit coupling (SOC). Comparative studies between solution and solid phases showed that molecular packing in crystalline state effectively suppresses structural distortion, significantly enhancing radiative transition efficiency by reducing non-radiative decay. The planar geometry-enabled fast ISC/RISC cycling ensures efficient triplet exciton utilization, leading to high-performance thermally activated delayed fluorescence (TADF). Our work provides molecular-level insights into the TADF mechanism of Cu-CMA systems, particularly revealing a non-conventional exciton conversion mechanism governed by the “weak SOC-small ΔE_ST-low λ″ synergy, which offers new design principles for developing cost-effective, high-efficiency copper-based TADF materials.

Keywords

Thermally activated delayed fluorescence / Cu(I) carbene-metal-amide (CMA) complex / Structure-property relationship / Weak spin-orbit coupling limitation / Cooperative singlet-triplet energy gap and reorganization energy

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Jilin University, The Editorial Department of Chemical Research in Chinese Universities and Springer-Verlag GmbH