Design, Synthesis And Electroluminescent Properties Of Tetraphenylethene-based AIE Molecules

During the past decades, Organic Light-Emitting Diodes (OLEDs) have shown promising application prospects in full-color display and solid-state lighting resources. However, there are still some difficulties to be overcome for further practicability. For example, to realize full-color displays, it is essential to obtain red-, green-and blue-emitters with equal stability and good electroluminescence (EL) efficiencies. So far, due to the intrinsic large bandgap of blue luminogens, the performance of blue OLEDs is often inferior to that of their red and green counterparts, which have already meet the needs for applications. Moreover, when fabricated as thin solid films in OLEDs, most conventional emitters suffer badly from the notorious aggregation-caused quenching (ACQ) effect. The discovery of aggregation-induced emission (AIE) molecules in2001have intrinsically solved the ACQ problem, and consequently, AIE-active luminogens exhibit great potential in the field of OLEDs due to their high solid-state quantum efficiencies. Although a lot of efficient AIE molecules have been reported, blue or deep-blue AIE emitters are still very scarce owing to the intrinsic extension of ?-conjugation by utilizing conventional linkage ways. Thus, it is still a challenge to design and synthesize AIE fluorophores with both blue emission and good electroluminescent performance.The reseach of the thesis is focusing on the design and synthesis of blue and deep-blue AIE materials in non-doped OLEDs. The main contents and results are as follows:In Chapter1:The historic development and bottlenecks of OLEDs, and the phenomenon and mechanism of AIE molecules were outlined. Then the application of AIE materials in OLEDs was mainly reviewed. And finally the synthetic ideas of the thesis were put forward.In Chapter2:Three benzene-cored fluorophors with tetraphenylethene (TPE) moiety peripheries (PhTPE, Ph2TPE and Ph3TPE) were designed and synthesized. The introduction of the bulky TPE units will make the molecules more crowded and twisted in space, and it could partially disrupt the prolonged conjugation. These three luminophors exhibit blue emissions from457to488nm with Lmax, ?c, max and ?P, max up to3966cd m-2,5.0cd A-1and3.87lm W-1, respectively.In Chapter3:Two new TPE-based conjugated molecules SFTPE and TPE-2Cz, constructed by TPE and carbazole or spirofluorene moieties, have been designed and successfully prepared. Among them, TPE was linked to spirofluorene or carbazole by sharing one phenyl ring or through the single carbon-nitrogen bond, with the purpose of improving EL performance and ensuring limited intramolecular conjugation. Both of the two emitters exhibit blue emission with Lmax, ?c, max and ?p, max up to8196cd m-2,3.33cd A"1and2.10lm W-1, respectively.In Chapter4:Four BTPE derivatives mTPE-pTPE, mTPE-mTPE, oTPE-mTPE and oTPE-pTPE were designed and successfully obtained. By merging two simple TPE units together through different linking positions, the ?-conjugation length is effectively controlled to ensure deep-blue emission. Because of the minor but intelligent structural modification, all the four fluorophores exhibit deep-blue emissions with Lmax and ?c, max up to3266cd m-2and3.33cd A"1, respectively.In Chapter5:Three TPE trimers mTPE-2mTPE,pTPE-2mTPE and mTPE-2pTPE with meta-or para-linkage modes have been successfully synthesized. They all exhibit blue or deep-blue emissions with maximum current efficiency up to4.05cd A-1, further verifying the facile but ingenious approach of utilizing meta-linkage mode in longer conjugated systems.In Chapter6:Four2TPATPE derivatives pTPE-2mTPA, mTPE-2oTPA, mTPE-2mTPA and mTPE-2pTPA were successfully synthesized with certain structures. Thanks to the introduction of the3,3'-substituted TPE core, the ?-conjugation lengths are effectively restricted to ensure blue or deep-blue emission. The non-doped OLEDs based on these four emitters exhibit blue and deep-blue emissions with Lmax and ?c, max up to8160cd m-2and3.79cd A"1, respectively.In Chapter7:Two AIE-active luminogens (TPE-pTPA and TPE-mTPA) were successfully synthesized. For comparison, other six ones were prepared. Because of the introduced hole-dominated triphenylamine (TPA) and efficient fluorene groups through non-conjugated linkage mode, the ?-conjugation lengths of the obtained luminogens are effectively restricted to ensure their blue emission. The non-doped OLEDs based on TPE-pTPA and TPE-mTPA exhibited blue or deep-blue emissions, low turn-on voltages (3V), and high electroluminescence efficiencies with Lmax, ?c, max, and ?p, max up to26697cd m-2,3.37cd A-1, and2.40lm W-1, respectively.In Chapter8:Four new BTPE derivatives, namely Methyl-BTPE, Isopro-BTPE, Ph-BTPE and Cz-BTPE with alkyl or aromatic groups in the biphenyl core were designed and synthesized. The torsion angles of the two TPE units were varied by the ingenious introduction of additional groups with different size and conjugation degree, which could ensure the restriction of the conjugation lengths. The non-doped OLEDs based on these four emitters exhibit blue and deep-blue emissions with Lmax and ?c, max up to9911cd m-2and3.74cd A-1, respectively.In Chapter9:Three Methyl-BTPE derivatives mMethyITPE-pTPE, oMethyITPE-pTPE and oMethyl-BTPE with methyl groups in the biphenyl core were designed and synthesized. The torsion and conjugation degree of two TPE moieties or TPE itself could be varied by the steric hindrance effect of the methyl units.In Chapter10:Two Cz-BTPE derivatives Cz-mpBTPE and Cz-mmBTPE with carbazole groups were designed and synthesized. The device performance of Cz-BTPE could be well adjusted by changing the linking positions of TPE and carbazole. Compare to BTPE, all the devices based on the new emitters exhibit much blue-shifted emissions with Lmax and ?c, max up to13156cd m-2and5.64cd A-1, respectively.In Chapter11:Five triphenylamine-cored fluorophors with mTPE or MethylTPE moiety peripheries (TPA-3mTPE, TPA-3MethylTPE, MethylTPA-3pTPE, MethylTPA-3mTPE and MethylTPA-2MethylTPE) were designed and synthesized. The introduction of triphenylamine could improve both the hole-transporting ability and EL performance of the resultant molecules. Moreover, the intramolecular conjugation lengths could also be effectively shortened by changing linkage ways or adding methyl groups. The device data have shown all the molecules possess good hole-transporting ability with Lmax and ?c, max up to19023cd m'2and8.03cd A-1, respectively.In Chapter12:Two AIE-active molecules Oxa-pTPE and Oxa-mTPE constructed by TPE and oxadiazole groups were designed and synthesized. The TOF measurements have shown the two molecules have bipolar-transporting characteristic. When served as fluorescent host materials in doped sky-blue OLEDs, they all exhibit high efficiencies with Lmax, ?c, max,?p, max and ?ext, max of10070cd m-2,9.79cd A-19.92Im W-1and5.0%, respectively.