Decoding Vibrational Contributions and Exciton Dynamics in TADF Emitters for Enhanced OLED Efficiency

Thermally activated delayed fluorescence (TADF) compounds play a pivotal role in enhancing the efficiency of organic light-emitting diodes (OLEDs) by enabling effective triplet exciton utilization, often facilitated by vibrational assistance. While multiresonant TADF systems benefit from rigid planar structures that suppress nonradiative decay, traditional donor-acceptor-donor (D-A-D) systems are more prone to nonradiative losses with their flexible single-bond connections. This study investigates three structurally similar D-A-D TADF compounds with distinct external quantum efficiencies to uncover the factors influencing their performance. Our analysis identifies specific vibrational modes that either enhance radiative transitions or contribute to nonradiative decay, emphasizing the critical role of vibrational dynamics. Using Huang-Rhys factor and exciton-phonon coupling, we demonstrate how these vibrational modes govern exciton dynamics. The Herzberg-Teller effect emerges as a key mechanism driving thermally activated performance, with vibrational corrections significantly improving the accuracy of rate predictions. The computed radiative and nonradiative rates show satisfactory agreement with experimental data, validating the robustness of our computational protocol. These findings provide actionable insights into the molecular design of TADF emitters, offering strategies to optimize OLED performance by balancing the interplay between vibrational dynamics and electronic transitions.