Synthesis And Properties Of Organic Luminescent Materials Based On Carbazole And Phenothiazine Derivatives

Organic light-emitting diodes (OLEDs) have attracted a great deal of attention, due to their practical application of the low turn-on voltage, full color display, high brightness in large-area flat-panel displays and solid-state lighting. One of the key developments is the design of hole-transporting materials with high HOMO energy levels to reduce the energy barrier between the ITO anode and the emitting layer; on the other hand, bipolar materials with intramolecular charge-transfer (ICT) behavior incorporating both hole-and electron-transporting segments also have been one of the topics in the synthetic organic field, because they not only can effectively simplify the device structure with double layers or even a single layer, but also have attractive application in the field of life science, environmental science and so on. In this dissertation, a series of hole-transporting materials based on carbazole and indolo[3,2-b]carbazole were designed and synthesized, and their optoelectronic properties were investigated. Furthermore, bipolar materials with phenothiazine unit as electron donors and [1,3,4] oxadiazole unit as electron acceptors were designed and synthesized. Then their optoelectronic and ICT properties were studied in detail. The main parts of this dissertation are as follows:1. Four star-burst compounds containing carbazole and triphenylamine units were synthesized and characterized. Their photophysical and electrochemical properties were extensively investigated. These materials absorbed in the region of332-339nm, and they all emitted in the blue region (λem=421-435nm). They were good candidates as hole-transporting/injection materials for OLEDs because of the high HOMO levels (-4.99--4.90eV). C4could expect to be blue material with a quantum yield of0.37.2. Three compounds based on indolo[3,2-b]carbazole were synthesized and characterized. Their photophysical and electrochemical properties were studied thoroughly. These materials all emitted in the blue region (λem=430-435nm). Their HOMO energy levels (-5.14--4.93eV) were close to the work function of the ITO anode facilitating the reduction of an energy barrier at the interface of ITO/HTL. These indolo[3,2-b]carbazole derivatives possessed high quantum yields, and showed potential application as hole-transporting materials for OLEDs.3. A series of bipolar compounds with phenothiazine as electron donor and [1,3,4]oxadiazole as electron acceptor were designed and synthesized. These compounds emitted in the region of481-569nm in dichloromethane, and had large Stocks shifts (133-179 nm). Cyclic voltammetry showed that these materials had high HOMO energy levels with incorporating phenothiazine units, implying that they had well hole-transporting peoperties. These compounds could be applied as good emitter with hole-transporting ability.4. The large positive solvatochromism of a series of phenothiazine derivatives in different solvents suggested significant intramolecular charge-transfer behavior between the donors and acceptors. Lippert-Mataga equation which expressed the Stokes shift as a function of the solvent polarity parameter△f[ε,n) were used to obtain more information about the change in the dipole moment upon excitation. Their dipole moment changes were evaluated. The large red shifts were120nm between aprotic solvents and protic solvents, indicating that these compounds were very sensitive to the polarity of the solvents. These compounds were expected to have potential applications in the field of detection of microenvironment polarity, biological molecules, dynamics of optical, diagnosis of medical and the two-photon absorption.Finally, all the compounds could be solution-processible materials because of their good solubility in organic solvents, and they possessed high quantum yields with large Stocks shifts. These compounds were candidates as blue, blue-green or green materials for OLEDs or other fields.