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

Abstract

Developing efficient "hot exciton" thermally activated delayed fluorescence (TADF) materials in electroluminescence has always been a significant and challenging issue. Herein, we have designed and synthesized two deuterated yellow emitters BT-2PhCz-d 10 and BT-2PhCz-d 24 based on the commonly designed hot exciton emitter BT-2PhCz to improve the exciton utilization efficiency. Transient absorption (TA) kinetic analysis showed that deuterated BT-2PhCz-d 10 and BT-2PhCz-d 24 possessed shorter delayed lifetimes and a faster high-lying reverse intersystem crossing rate constant (k h-RISC ) than BT-2PhCz. The measured photoluminescence quantum yield (PLQY) and infrared spectrum results also experimentally confirmed that the introduction of C− D bonds played a key role in suppressing nonradiative processes. The optimized organic light-emitting diodes (OLEDs) based on these hot exciton materials exhibited a maximum external quantum efficiency (EQE) of 7.1% for BT-2PhCz, 10.0% for BT-2PhCzd 10 , and 11.8% for BT-2PhCz-d 24 , respectively, corresponding to exciton utilization efficiencies of 39.3−26.2, 50.0−33.3, and 59.4− 39.6%. These results confirm that the deuterated isotope effect realized the regulation of high-energy spin flip processes and nonradiative decay processes, providing a new strategy for designing high-performance hot exciton emitters.

Unravelling the photobehavior of a 2,1,3-benzothiadiazole-based HOF and its molecular units: experimental and theoretical insights into their spectroscopic properties in solution and in the solid state

“…BTD derivatives also display slow photodynamics due to the existence of accessible triplet states. 62,66,67,74 Our results from the theoretical calculations on BTIA-ester in DMF (Section 3.1) show the possibility of an ISC process between the S 1 and T 2 states (Δ E S 1 / T 2 = 0.326 eV), leading to species which may populate the T 2 state. To explore the slow relaxation of BTIA-ester and BTIA-COOH in DMF solutions, we carried out ns–ms flash photolysis experiments upon excitation at 355 nm in presence and absence of molecular oxygen.…”

“…61 Comparable energy gap values (Δ E S 1 / T 2 = 0.277 eV and Δ E T 1 / T 2 = 0.972 eV) have been observed in other BTD derivatives, which undergo a RISC process. 62 The HOMO−1 transition involved in the T 2 state exhibits significantly higher contributions from the BZ fragment and sulphur atom, with a lesser contribution from the MBZ moiety compared to the HOMO transition associated with the S 1 state. This results in considerable differences in the CT character of the S 1 and T 2 states.…”

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

“…The devices based on perdeuterated emitters exhibit a EQE max of 33.1% and a lifetime to reach 80% of the initial luminance of 1365 h with a CIE y coordinate of 0.20 at a luminance of 1000 cd m –2 , which outperforms blue PHOS OLEDs. Recently, we found that the introduction of deuterium atoms could become an efficient strategy for designing high-performance hot exciton emitters. Two deuterated emitters, BT-2PhCz-d10 and BT-2PhCz-d24 , based on the commonly designed hot exciton emitter BT-2PhCz were designed and synthesized.…”