Effects of Different Eelectron-withdrawing Moieties on the General Photoelectric Properties of Fluorene-based Dimers
YUAN Xinlei, LIJie, LU Zhiwei, YE Shanghui, JIANG Hongji
2020, 36(6):
1174-1182.
doi:10.1007/s40242-020-0191-2
Abstract
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Here, 9,9,9'-tris(4-butoxyphenyl)-9H-9'H-2,2'-difluorene(DF) was synthesized as a reference for compa-rison, 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'-bif-luorene]-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℃ 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.
