AUTHOR=Sohn Sunyoung , Ha Min Woo , Park Jiyong , Kim Yoo-Heon , Ahn Hyungju , Jung Sungjune , Kwon Soon-Ki , Kim Yun-Hi 

TITLE=High-Efficiency Diphenylpyrimidine Derivatives Blue Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes

JOURNAL=Frontiers in Chemistry

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.00356

DOI=10.3389/fchem.2020.00356

ISSN=2296-2646

ABSTRACT=<p>Organic light-emitting diodes with thermally activated delayed fluorescence emitter have been developed with highly twisted donor–acceptor configurations and color-pure blue emitters. Synthesized 4-(4-(4,6-diphenylpyrimidin-2-yl)phenyl)-10H-spiro[acridine-9,9′-fluorene] (4,6-PhPMAF) doped device with spiroacridine as a donor unit and diphenylpyrimidine as acceptor exhibits the device characteristics such as the luminescence, external quantum efficiencies, current efficiencies, and power efficiencies corresponding to 213 cd/m<sup>2</sup>, 2.95%, 3.27 cd/A, and 2.94 lm/W with Commission International de l'Eclairage (CIE) coordinates of (0.15, 0.11) in 4,6-PhPMAF-doped DPEPO emitter. The reported 10-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-10H-spiro[acridine-9,9′-fluorene] (2,6-PhPMAF) doped device exhibit high device performance with 1,445 cd/m<sup>2</sup>, 12.38%, 19.6 cd/A, and 15.4 lm/W, which might be originated from increased internal quantum efficiency by up-converted triplet excitons to the singlet state with relatively smaller Δ<italic>E</italic><sub>ST</sub> of 0.17 eV and higher reverse intersystem crossing rate (<italic>k</italic><sub>RISC</sub>) of 1.0 ×10<sup>8</sup>/s in 2,6-PhPMAF than 0.27 eV and 3.9 ×10<sup>7</sup>/s in 4,6-PhPMAF. Despite low performance of 4,6-PhPMAF doped device, synthesized 4,6-PhPMAF has better color purity as a deep-blue emission with <italic>y</italic> axis (0.11) than reported 2,6-PhPMAF with <italic>y</italic> axis (0.19) in CIE coordinate. The synthesized 4,6-PhPMAF has higher thermal stability of any transition up to 300°C and decomposition temperature with only 5% weight loss in 400°C than reported 2,6-PhPMAF. The maximum photoluminescence emission of 4,6-PhPMAF in various solvents appeared at 438 nm, which has blue shift about 20 nm than that of 2,6-PhPMAF, which contributes deep-blue emission in synthesized 4,6-PhPMAF.</p>