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

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

doi:10.3389/fchem.2020.00356

Abstract

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/m2, 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/m2, 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 ΔEST of 0.17 eV and higher reverse intersystem crossing rate (kRISC) of 1.0 ×108/s in 2,6-PhPMAF than 0.27 eV and 3.9 ×107/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 y axis (0.11) than reported 2,6-PhPMAF with y 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.

Highlights

The organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) material have been widely investigated for high-efficiency device performance or low triplet and singlet energy levels for reduced driving voltage by narrow host bandgap, since the Adachi group reported the intersystem crossing (ISC) and reverse intersystem crossing (RISC) for triplet-to-singlet state conversion (Goushi et al, 2012; Nakanotani et al, 2014; Kim et al, 2015)
The chemical structure of the synthesized intermediates and 4,6-PhPMAF were characterized by nuclear magnetic resonance (1H-NMR, 13C-NMR) spectroscopy and mass spectroscopy
The performance of reported 2,6PhPMAF doped TADF device is over four times higher than synthesized 4,6-PhPMAF doped device

Summary

INTRODUCTION

The organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) material have been widely investigated for high-efficiency device performance or low triplet and singlet energy levels for reduced driving voltage by narrow host bandgap, since the Adachi group reported the intersystem crossing (ISC) and reverse intersystem crossing (RISC) for triplet-to-singlet state conversion (Goushi et al, 2012; Nakanotani et al, 2014; Kim et al, 2015) It can harvest both single and triplet excitons because TADF involves small singlet–triplet state energy splitting by thermally activation (Tao et al, 2014; Sun et al, 2016; Cui et al, 2017). Based on the reported linker material and molecular orientation, we analyzed the properties of synthesized emitters with spiroacridine-based electron donor (D) and diphenylpyrimidine group of electron acceptor (A) with different substance nitrogenous position

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT