Design, Synthesis And Photoelectric Properties Of Solution-processible Aggregation-induced Emitting Materials Containing Vinyl Units

Organic fluorescent materials are widely used in flat panel displays, lighting equipment, optical sensors, photovoltaic cells, bio-imaging and other fields. Over recent years, organic electroluminescent device(OLED) products gradually occupy the market, significantly reducing costs has become a key factor to improve competitiveness. Low-cost solution processing techniques is expected to large-scale application in the field of flat panel displays. Small molecules show significant advantages, such as welled fined molecular structures, facile purification by standard techniques, and specific structure – property correlations. Traditional organic fluorophores are commonly emissive in the dilute solution but become weak or nonemissive when in the solid state due to aggregation-caused quenching(ACQ), greatly limits the application of the material. Since 2001, the aggregation-induced emission phenomenon(AIE) have been proposed, a large number of materials with AIE properties was reported. Such materials emit strongly in the aggregated or solid state while it is nonemissive in the dilute solution, so it has great application prospects.A lot of luminescent materials about fluorene(including spiro fluorene and multi-fluorenyl) were studied and reported due to high luminous efficiency。2,7-position of fluorene is very lively and very easy to electrophilic substitution reaction. While the 9-position of fluorene can be alkylated to improve the solubility of the compound. At the same time this site can also connect a bulky aromatic group to inhibit the formation of close packing and avoid the exciplex. Therefore, the compound has good thermal stability and high luminous efficiency in solid state. Among the AIE materials, tetraphenyl ethylene(TPE) and its derivatives attracted more and more attention due to simple synthesis, high luminous efficiency and easy to modify.In summary, this paper will bind AIE molecules and fluorene derivative. Tetraphenyl ethylene(TPE) and its derivatives as a central core and fluorenyl alkyl chain carbazolyl group as peripherals, this design makes the main chain of molecule as a luminescent center to ensure high luminous efficiency. The introduction of alkyl chains improved molecular flexibility and in favor of the processing solution. The introduction of a carbazole unit increases the rigidity of the molecule and improve the thermodynamic properties of the molecule, at the same time carbazole unit may further increase the hole transport properties of molecules. To achieve the goal, we carried out the following studies:1. Three compounds of different central core is designed and synthesized. Three molecular emit weakly or even completely quenched in solution but show high luminous efficiency in the solid state. The fluorescence quantum yield of TPE-DFCZ powder up to 93%. Three molecules have AIE effect by the spectrum of compounds in tetrahydrofuran / water solvent. By studying the mechanism of AIE, we found not only has rotation of C-C, as well as cis and trans configurations conversions in dilute solution.2. In the third chapter, we replaced one or two phenyl ring(s) of TPE by cyano to obtain two compounds SCNTPhE-DFCZ and DCNDPhE-DFCZ. They all have AIE effect by the spectrum of compounds in tetrahydrofuran/water solvent. The energy-gap of two compounds were smaller than TPE-DFCZ by electrochemical tests, and the energy-gap decrease more with the increasing number of cyano group. By comparing several spectra of thin films of different compounds, we found the charge transfer from the carbazolyl group to the central core in DCNDPhE-DFCZ. Similarly, we found DCNDPhE-DFCZ not only has rotation of C-C, as well as cis and trans configurations conversions in dilute solution. We separated the two configurations of cis and trans of DCNDPhE-DFCZ. By series of characterization, we found the thermodynamic properties of isomer were same. The emission peak of film located at 600 and 587 nm and the ηPL of spin-coated films reached 44% and 40%, respectively. The device of isomers display emission peak at 596 and 586 nm and the maximum brightness reached 2114 cd m-2 and 1741 cd m-2, respectively. The character of isomer only have slight difference. These data illustrate that the configuration has a small effect to the performance of molecule and enriched AIE molecular system.