Ling Qi-dan
2008
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Journal
Journal of Nanjing University of Posts and Telecommunications
Abstract
In order to correlate the electro-optical properties of fluorene-based oligomers with different molecular architecture, 9,9-didodecyl-fluorene (F1) segments were coupled with 2,4-difluorophenyl boronic acid by Suzuki reaction to give a series of target oligomers, 2-(2,4-difluorophenyl) -9,9-didodecyl-fluorene (FF1), 2,7-bis(2,4-difluorophenyl)-9,9-didodecyl-fluorene(FF2),2-(2-(2,4-difluorophenyl)-9,9-didodecyl-fluoren)-7-(2,4-difluorophenyl)-9,9-didodecyl-fluorene(FF3),and 1-bromo-3,5-bis(2-(2,4-difluorophenyl)9,9-didodecyl-fluoren)-benzene(FF4). The molecular structures of FF3 and FF4 are fully characterized by 1H-NMR, MALDI-TOF mass spectrometry and elemental analysis, respectively. Absorption and emission spectra show that the absorption maximum attributed to π-π nature of the excitation is red-shifted in the turn of F1, FF1, FF2,and FF3, and the maximum absorption peak of FF4 occurs to be blue-shifted, while the maximum photoluminescence emission of FF4 film is red-shifted relative to that of FF3. Density functional theory (DFT) calculations provide further evidence that the energy band gaps of oligomers are decreased with increasing the conjugated length. At last, the interesting photostability attributed to the molecular architecture and fluorine element are also observed and discussed.