Synthesis Of Quinazoline Derivatives And Their Applications In Organic Light Emitting Devices

Organic light-emitting diodes (OLEDs) have attracted a great deal of scientific andcommercial interest owing to their promising applications in flat-panel displays andsolid-state lighting sources. Normally, the phosphorescent OLEDs (PhOLEDs) usingorganic phosphor have higher electroluminescent (EL) efficiency than theconventional fluorescent OLEDs, mainly because of the harvest of the triplet exciton.A widely demonstrated effective strategy towards the suppression of the tripletexciton quenching within the emissive layer (EML) is dispersing the phosphorescentdyes in a host material to construct an EML with a small phosphor-phosphor contactto avoid the negative effect caused by the aggregation of the triplet excitons. So,further investigations on novel high-performance host materials still need moreresearch effort. On the other hand, in most cases, white organic light-emitting diodes(WOLEDs) are made from combinations of either the individual R-G-B luminescenceor complementary colour pairs. Therefore, the corresponding full-color and whiteOLEDs often resulted in a complex material system and high-cost organic synthesis.Considering this, we designed and synthesized seven optoelectronic molecules withn-type semiconductor quinazoline moiety, fabricated monochromatic PhOLEDs andwhite OLEDs with high efficiency, and intended to establish the relationship between the structures and properities.1. In chapter II, two quinazoline derivatives connected with3,6-position of9-phenylcarbazole have been designed and synthesized. The photophysical measurementsindicate that these two compounds have obvious intramolecular charge transfer andhigh triplet energy level. Theoretical calculation shows that they have obviousdelocalized electron cloud distribution, indicating that they own both hole andelectron transport abilities. High-performance yellow and red phosphorescent devicesusing them as host materials are fabricated and the disubstituted one exhibits betterperformance. The power efficiency and brightness are56.98lm W-1,32262cd m-2and16.49lm W-1,18144cd m-2for the yellow and red devices respectively. Consideringthe performance of single-carrier devices, the bipolar host material with morebalanced carrier injection/transport property gets efficient OLEDs.2. In chapter III, two centrosymmetric derivatives were synthesized by coupling threequinazoline units with1,3,5position of benzene. Photophysical and electrochemicalmeasurements indicate that these two compounds have lower LUMO level and largerenergy gap. It concludes that the doped films form exiplex from fluorescenceemission and lifetime measurement of the TCTA doped films. Through the differentdoping concentration of red phosphor guest material, it confirms that the exciplex canbe host material for PhOLEDs and the energy can transfer from exciplex to redphosphor completely. The devices, using the red phosphor doped in the exciplex asemissive layer, exhibit power efficiency of22.72lm W-1and external quantumefficiency of14%. The single-carrier devices indicate that the exciplex formingco-host improve the hole transport ability of the materials and result in efficientOLED. 3. In chapter IV, one compound by coupling two quinazoline units with anthracene at9,10-position was synthesized. X-ray diffraction indicates that the quinazoline unitseffectively avoid π···π interaction which commonly exists in most anthracenederivatives, it stacks mainly by C–H···π intermolecular interactions. Thephotophysical and electrochemical measurement indicate that the film of thecompound exhibits pure blue light and it has suitable energy level. Theoreticalcalculation shows it has obvious delocalized electron cloud distribution, indicates thatit owns both hole and electron transport ability. Doping orange phosphor withdifferent concentration, indicates that it can get white emission through incompleteenergy transfer. The single-carrier devices indicate that the compound has excellentcarrier transport properties. The white OLED using the doped film as emissive layerhas brightness of24340cd m-2, power efficiency of13.64lm W-1, CIE coordinates of(0.33,0.36), and exhibits excellent chroma stability.4. In chapter V, two quinazoline derivatives connected with electron-donating groupcarbazole and diphenylamine have been designed and synthesized through simplesynthetic procedure. They exhibit intramolecular charge transfer properties. Study onthe photophysical properties shows that the solution displays obvious solvation effectand protonation effect. The emission of the film doping with camphorsulfonic acidlead to obvious red shift. Further studies show that energy transfer process existsbetween the neutral molecule and protonated molecule, which can generate stablewhite light emission through controlling the doping concentration. Using thecamphorsulfonic acid doped film as emissive layer, we obtained the white OLED withbrightness of13180cd m-2and power efficiency of5.14lm W-1. What’s more, it hashigh color purity and spectral stability with colour index of86and CIE coordinates of(0.36+0.02,0.34+0.01). In summary, we have designed and synthesized seven organic optoelectronicmolecules owning quinazoline unit, which were applied in flat-panel displays andsolid-state lighting sources. The relationship between structures and properties havebeen carefully investigated and the divices based on these materials exhibit excellentperformance. So, this paper will play a positive role in both broadening photoelectricmaterial system and optimizing device structure.