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.