With Fluorene - Benzene Structure Of Conjugated Organic Materials Design, Synthesis And Optical And Electrical Properties

The development of organic electroluminescent materials is one of the forefronts and hot areas of the optoelectronic information materials, on account of the advantages of organic electroluminescent materials relative to those of inorganic counterparts. Fluorene and its derivatives, which have an aromatic biphenyl structure with wide energy gap in the backbones and high luminescent efficiency, have drawn more and more attention of materials chemists and device physicists. In this thesis for Ph. D program, the progress about fluorene-containing electroluminescent materials from the domestic and abroad as well as our own work in the past few years is reviewed. Some issues to be addressed and hotspots to be further investigated are also discussed. On basis of above presentation, the key points of correlation between the structures of fluorene-containing materials with different molecular architecture and their photoelectric properties for Ph. D program is issued in turn. The detailed results of this thesis are listed as below,1: In order to contrast the general properties of fluorene oligomers with different molecular architecture, 9,9-didodecyl-fluorene (F0) segments was 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 structure of FF3 and FF4 is fully characterized by ¹H NMR, MALDI-TOF mass Spectrometry and elemental analysis, respectively. Absorption and emission spectra show that the absorption maximum attributed to Ï€-Ï€^* nature of excitation is red-shifted in the turn of F0, FF1, FF2 and FF3, however, the maximum absorption of FF4 occurs to be blue-shifted, while the photoluminescence emission of FF4 film is red-shifted relative to that of FF3. Density functional theory (DFT) calculations provide further evidence that the band gaps of the oligomers are reduced with increasing of the conjugated length. The interesting photostability attributed to the fluorine element is also observed and discussed.2: a Y-shaped fluorene-based oligomer (3F) on the basis of parent oligomer (1F and 2F) has been synthesized to investigate the optical relationships between the Y-shaped oligomer and its parent oligomers. The primary experimental and theoreticalinvestigation demonstrates that the optical properties of the oligomers are strongly affected by the molecular frameworks.3: To ascertain the influence of the position and size of substituents, as well as interactions among luminophors, on the photophysical properties of parent oligomers, a set of novel oligomers (F0, F1, and F2 containing one central fluorene unit) based on trifluorene symmetrically end-capped with 2,4-difluorobenzene, fluorine, or pyridine derivatives with linear or branched molecular framework were designed and conveniently synthesized via Pd(0)-catalyzed Suzuki coupling reaction. The molecular structure and optical properties of the oligomers were fully characterized by ¹H NMR, ¹³C NMR, MALDI-TOF, UV-vis, PL, cyclic voltammogram and steady-state time-of-flight photoluminescence decaying spectra. The general experimental results demonstrated that the optical property and energy level of F2 took on some abnormal characteristics relative to those of F0 and F1, while the decaying process of F2 and F1 showed some model different from that of F0.4: In order to investigate the fine photoelectric difference of the target oligomers with or without peripheral fluorene moieties, two thermal stable oligomers:4-(4-(9,9-dibutyl-2-(4-(2,6-diphenylpyridine)phenyl)-fluoren)phenyl)-2,6-d iphenyl pyridine and 4-(4-(2-(4-(2,6-bis(4-(9,9-dibutyl-fluoren)phenyl)pyridin) phenyl-9,9-dibutyl-fluoren)phenyl)2,6-bis(4-(9,9-dibutyl-fluoren)phenyl)pyridine had been designed and convergently prepared via Pd (0)-catalyzed Suzuki coupling reaction. The molecular structures of the oligomers were fully characterized by ¹H NMR, ¹³C NMR, and MALDI-TOF, respectively. The absorption, emission behavior and band gaps of the oligomers were examined through UV-vis, photoluminescent spectrum and cyclic voltammogram. The experimental results demonstrated that the absorption, photoluminescent and energy band gaps were little affected by molecular architecture, while the absolute photoluminescent quantum efficiency and electroluminescent performance were strongly correlated with the molecular frameworks.5: In order to investigate the fine photoelectric difference of the target polymers with diverse molecular architecture, a serials of polymers (P0, P1 and P2) were synthesized by polymerizing of 2,7-bis(trimethylene boronate)-9,9-dioctylfluorene with mixtures of 2,7-dibromo-9,9-dioctylfluorene and 2, 4, 6-tris(4-phenyl)pyridine derivatives with different feeding rate using the palladium-catalyzed Suzuki coupling reaction. The molecular structure of the monomers and polymers were fullycharacterized by ¹H NMR, ¹³C NMR, Gel permeation chromatography (GPC) and MALDI-TOF, respectively. The absorption and emission behavior of the polymers were examined through UV-vis and photoluminescence spectra. The experimental results demonstrated that all classes of materials provided wide-band-gap polymers that emitted in the blue region of the electromagnetic spectrum and the absorption and photoluminescence behavior of P0 and P1 were little affected by molecular architecture, while those of P2 were strongly correlated with the hyperbranched molecular frameworks. Cyclic voltammetry studies on these three polymer films pointed out the lower HOMO energy level and wider band gap of P2 relative to those of P0 and P1. The absolute photoluminescence quantum efficiency and photoluminescence stability showed some rules correlated strongly with molecular conformation under same annealing condition. The new polymers were all thermally stable up to 410℃. The results of electroluminescent diodes demonstrated that polymer P1 was a better alternation of organic light-emitting diode application, and the keto in polyfluorene might be the real origin of the long wavelength emission in polyfluorene.