AUTHOR=Liu Junyuan , Zhou Keren , Wang Dan , Deng Chao , Duan Ke , Ai Qi , Zhang Qisheng 

TITLE=Pyrazine-Based Blue Thermally Activated Delayed Fluorescence Materials: Combine Small Singlet–Triplet Splitting With Large Fluorescence Rate

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00312

DOI=10.3389/fchem.2019.00312

ISSN=2296-2646

ABSTRACT=<p>Metal-free thermally activated delayed fluorescence (TADF) emitters have emerged as promising candidate materials for highly efficient and low-cost organic light-emitting diodes (OLEDs). Here, a novel acceptor 2-cyanopyrazine is selected for the construction of blue TADF molecules via computer-assisted molecular design. Both theoretical prediction and experimental photophysical data indicate a small S<sub>1</sub>-T<sub>1</sub> energy gap (Δ<italic>E</italic><sub>ST</sub>) and a relative large fluorescence rate (<italic>k</italic><sub>F</sub>) in an <italic>o</italic>-phenylene-bridged 2-cyanopyrazine/3,6-di-<italic>tert</italic>-butylcarbazole compound (TCzPZCN). The <italic>k</italic><sub>F</sub> value of 3.7 × 10<sup>7</sup> s<sup>−1</sup> observed in a TCzPZCN doped film is among the highest in the TADF emitters with a Δ<italic>E</italic><sub>ST</sub> smaller than 0.1 eV. Blue TADF emission is observed in a TCzPZCN doped film with a short TADF lifetime of 1.9 μs. The OLEDs using TCzPZCN as emitter exhibit a maximum external quantum efficiency (EQE) of 7.6% with low-efficiency roll-off. A sky-blue device containing a derivative of TCzPZCN achieves an improved EQE maximum of 12.2% by suppressing the non-radiative decay at T<sub>1</sub>.</p>