Synthesis Of Novel Blue Light Emitting Materials And Their Opto-electronic Properties

In recent years, organic light-emitting diode(OLED), especially blue organic light-emitting diode, have attracted growing attentions due to their great application potentials in optoelectronic devices. As we know, it is difficult to prepare the blue light emitting diode with excellent properties for small molecule OLED device or polymer OLED device. In this thesis, from the perspective of the starting materials, a series of novel small molecule materials and fluorene-containing copolymers were designed and synthesized. And their optical performances, energy levels and electrochemical properties were studied and analyzed. The main contents are as follows:In Chapter 2, the materials of DPS-DAC-C4 DPS-DAC-Ph DPS-DAC-Ph-CZ and DPS-DAC-Ph-TPA employing thermally activated delayed fluorescence(TADF) were synthesized by introducing n-butyl, p-tert-butyl-phenyl, carbazolyl and triphenylamine on 9,10-dihydro-acridine acted as electron donor units, respectively, in which process the diphenyl sulfoxide acted as electron acceptor units. By studying their optical properties and electrochemical properties, it showed that the molecules with electron-rich groups, such as carbazole and triphenylamine, were much easily to be oxidized, which rised the HOMO level. The rising of HOMO level decreased singlet–triplet energy gaps △EST, which would increase the efficiency of triplet excitons to singlet excitons. As a result, the properties of OLED devices would be improved. On the other hand, group with alkyl was introduced into 9,10-dihydro-acridine to improve the solubility of molecule, which enhanced the interfacial compatibility between emitting layer and transport layer. The above four molecules, with optical bandgaps about 3.0 e V, are blue light emitting materials with great potentials.In Chapter 3, in order to solve the stability problem for polymer blue OLED devices, we proposed to introduce a styrene unit in the polymer side chain. Then the polymer chains were corosslinked throuth carbon-carbon double bond thermal crosslinking. This method would improve the stability of the polymer. Novel polyfluorenes containing different amounts of styrene units using the Suzuki reaction, namely PFCTV10 PFCTV20 PFCTV30 PFCTV40 PFCTV50 and PFCTCV20, respectively, were synthesized. By studying their optical properties and electrochemical properties, the best properties of polyfluorenes containing styrene units would be selected. At the same time, because of the low HOMO level of fluorene homopolymers(EHOMO=-5.8e V), it was very difficult to inject holes from PEDOT:PSS(EHOMO=-5.2e V). Therefore electron-rich groups, such as carbazole and triphenylamine, were introduced to the side chains of polyfluorenes. Holes injected from the anode in PEDOT:PSS would be readily transported to the TPA or Cz moieties due to the nearly energy-free barrier. Moreover it could afford to balance charge carrier injection/transport in the concerned device. Obviously, those thermal crosslinking polyfluorenes are very promising for blue light emitting materials.