Effects of Different Eelectron-withdrawing Moieties on the General Photoelectric Properties of Fluorene-based Dimers
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doi: 10.1007/s40242-020-0191-2
Article
Effects of Different Eelectron-withdrawing Moieties on the General Photoelectric Properties of Fluorene-based Dimers YUAN Xinlei, LI Jie, LU Zhiwei, YE Shanghui and JIANG Hongji* Key Laboratory for Organic Electronics and Information Displays and Jiangsu Key Laboratory for Biosensors, Jiangsu National Synergetic Innovation Center for Advanced Materials, Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, Nanjing 210042, P. R. China Abstract Here, 9,9,9′-tris(4-butoxyphenyl)-9H-9′H-2,2′-difluorene(DF) was synthesized as a reference for comparison, and diphenyl sulfone and triphenylphosphine oxygen were introduced to the 9-position of fluorene through a C―H coupling reaction to produce two fluorene-based oligomers 9′,9′′′-[sulfonylbis(4,1-phenylene)]bis[9,9,9′-tris(4-butoxyphenyl)-9H,9′H-2,2′-bifluorene](DF)2SO2 and phenylbis(4-{9,9′,9′-tris(4-butoxyphenyl)-9H,9′H-[2,2′-bifluorene]-9-yl}phenyl)phosphine oxide[(DF)2PO]. Solid powders of all the three compounds exhibit excellent thermal stability with thermal temperature at 5% mass loss of 375, 429 and 383 °C for (DF) 2SO2, (DF)2PO and DF. In addition, owing to the distorted molecular structure and weak electron-absorbing ability of the acceptor, (DF) 2SO2 and (DF)2PO do not have obvious intramolecular charge transfer characteristics, and exhibit stable localized 394 nm/375 nm fluorescence emission peaks in different polar solvents. The absolute luminescence quantum efficiencies of (DF)2SO2, (DF)2PO and DF solid powders are 20.83%, 10.03% and 59.46%. Compound DF has the highest quantum yield as an electron donor. The chromaticity coordinates of the blue OLED devices based on DF and DF2SO2 fabricated by solution spin coating were (0.19, 0.10) and (0.19, 0.11), which were closest to the deep blue region, and the corresponding maximum external quantum efficiencies are 1.45% and 0.87%, respectively, which are higher than that of (DF) 2PO(0.25%) and consistent with the difference in the solid-state quantum efficiency between them. Keywords Organic light emitting-diode; Electron-withdrawing moiety; Fluorene; Diphenyl sulfone; Triphenylphosphine oxide
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Introduction
Organic electroluminescent materials have received increasing attention from scientists with the success of organic light emitting-diode(OLED) displays in the field of smartphones. Since only singlet excitons can be used to emit light, the efficiency of fluorescent materials is low, which cannot meet the requirements of practical applications[1,2]. Then phosphorescent materials were developed and applied in the lightemitting layer, and many high external quantum efficiency (EQE) phosphorescent OLEDs were prepared[3]. But the introduction of heavy metal elements in phosphorescent materials is unfriendly to production costs and environment[4,5]. To solve these problems, Adachi et al.[6] discovered a new light-emitting mechanism of thermally activated delayed fluorescence(TADF), which can achieve 100% internal quantum efficiency through reve
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