Design, Synthesis And Characterization Of Phenanthroimidazole Derivatives And Their Applications In Organic Light Emitting Devices (OLEDs)

Recently, much research on organic light-emitting devices (OLEDs) has been intensively pursued because of their applications in full-color display and solid-state lighting. In this thesis, three series of phenanthroimidazole derivatives were designed, synthesized and charachterized by Mass spectrum analysis, 1H NMR, 13C NMR, thermal analysis, spectroscopic analysis, X-ray diffraction analysis, respectively. Moreover, some theoritical calculations were carried out to study spatial distributions of front orbital of the materials. Because of their high thermal stability, good film forming ability, high quantum yield, we attached importance to their applications in organic light emitting devices (OLEDs). The main research results are summarized as below:1. We designed and synthesized phenanthroimidazole derivatives based on thiophene ring as the linker. By attaching different moiety in C5-position of thiophene ring, the electroluminescence color can be tuned from blue (494 nm) to green (531 nm). Furthermore, the introduction of the thiophene ring to C2-position of imidazole ring can render shallow HOMO energy (5.00-5.21 eV), decreasing the energy barrier of the hole-injection from hole-transport layer (NPB: 5.4 eV) to emitters, leading to high device performance with low onset voltage (< 2.7 V) and low driving voltage (lower than 5.5 V at 1000 cd/m2).2. We designed and successfully synthesized four materials with Donor-π-Acceptor structure by attaching electron-donating moiety of triphenylamine (TPA) at different positions of the phenanthro-imidazole with different linkers and investigated their applications as emitter layer in non-doped OLEDs. Trilayer device based on TPA-BPI shows excellent performance in terms of current efficiency, power efficiency, and external quantum yield of 2.63 cd/A, 2.53 lm/W, 3.08%, those are amongst highest OLEDs with CIEy < 0.10. Such device also demonstrates good color stability with CIE coordinates of (0.15, 0.09). By controlling the conjugation in the molecules, EL spectrum is further blue-shifted with CIE coordinates of (0.15, 0.05). In addition, the TPA-TPI based device exhibits a higher efficiency of 4.6 cd/A and 4.68 lm/W.3. By introducing of heterocyclic as well as other aromatic ring to the phenanthroimidazole skeleton, we obtained some organic materials and studied their applications in OLEDs. By introducing electro-donor and electro-acceptor to the imidazole skeleton, the potential application as electron-transport materials and hole-transport materials are investigated. In particular, TPA-TriPI can serve as hole-transport materials in the device with Alq3 as electro-transport materials and emitters, the device performance is as well as that of with classical NPB as the hole-transport layer.