Deuterium Renders Fast Risc and Low Non‐Radiation Decays of TADF Emitters

Abstract

A simple strategy to simultaneously achieve fast reverse intersystem crossing (RISC) and low non‐radiative decay rates in thermally activated delayed fluorescence (TADF) emitters is still lacking. Here, the green TADF emitters containing aromatic ketones and prepared D‐Ph and D‐PhCz containing different amounts of deuterium are deuterated to study the mechanism of deuterium on the performance improvement of TADF devices. Due to the heavy atom effect of deuterium, the non‐radiative transition rate constant (knr) of D‐Ph and D‐PhCz decreases. Most importantly, deuterium reduces the reorganization energy (λ) of (T1‐S1), which greatly improves the reverse intersystem crossing rate constant (kRISC) and the exciton utilization efficiency. The results show that the external quantum efficiency of D‐Ph and D‐PhCz increases to 25.69% and 24.92%, respectively. This study provides a simple and efficient strategy for reducing non‐radiative energy loss and increasing kRISC to achieve high‐performance TADF emitters.

Boosting Organic Light-Emitting Diodes Technology Using Thermally Activated Delayed Fluorescent Emitters: A Review

“…The primary reason for this positive effect was reported to correlate with an increase in the normal-mode displacement (Δ Q ) and Huang–Rhys factor ( S j ) of deuterated TADF. In 2023, the Wang group synthesized the terminal phenyl-deuterated emitter D-Ph and full-donor-deuterated emitter D-PhCz based on the thioxanthone-type TADF emitter 2,7-TXO-PhCz . The photophysical result revealed that the heavy-atom effect of deuterium in D-Ph and D-PhCz suppresses the structural relaxation and reduces k nr by 1.23 and 1.13 times, respectively, and improves k RISC and EUE as a result of the reduction of the reorganization energy (λ) of T 1 –S 1 , leading to suppression of the efficiency roll-off.…”

Novel Deuterated Benzothiadiazole Derivatives with Enhancing High-Lying Reverse Intersystem Crossing for High-Efficiency Organic Light-Emitting Diodes

“…Liao et al subsequently confirmed the potential of the deuterated isotope effect in suppressing nonradiative decay and intersystem crossing to improve luminescence efficiency from the perspective of theoretical calculations, but the actual device performance did not show significant improvements . Recently, our group reported two deuterated TADF molecules, D-Ph and D-PhCz, and experimentally confirmed the actual role of the deuterated isotope effect in suppressing nonradiative decay and promoting RISC . Inspired by these works, the deuteration effect is also expected to provide a solution to improve the exciton utilization of hot exciton TADF materials by accelerating hRISC.…”

“…It has been previously reported that some classic TADFs undergo significant changes in delayed lifetime and ISC/RISC rate after halogen substitution (Cl, Br, and I). − However, the halogen substitution strategy sometimes brings some negative effects to OLEDs: − for example, the enhancing intersystem crossing (ISC) will promote the accumulation of nonluminescent triplet excitons, causing emission quenching and more serious efficiency roll-off; the lower bond dissociation energy (BDE) of carbon–halogen bonds can lead to poorer stability at high current densities; different torsion angles of compounds after halogen modification significantly changed emission spectra. Introducing heavier deuterium isotopes to replace hydrogen atoms in C–H bonds, as an alternative strategy, has been used to modify host materials and TADF emitters to improve device stability and efficiency in recent years. − In 2021, Adachi et al unveiled that the better device stability of deuterated host PYD2Cz-d 16 with 1.7 times longer LT 95 was originated from stable amorphous properties and balanced carrier transport properties . Liao et al subsequently confirmed the potential of the deuterated isotope effect in suppressing nonradiative decay and intersystem crossing to improve luminescence efficiency from the perspective of theoretical calculations, but the actual device performance did not show significant improvements .…”