Aggregation-induced Emission Materials Based On Silole Derivatives: Design, Synthesis And Application

Due to their unique electronic structures, siloles have a low-lying lowest unoccupied molecular orbital(LUMO) energy level, which endows siloles with high electron acceptability, and make them ideal electron-transporting materials in optoelectronics. In 2001, it was discovered that this kind of compounds were almost non-fluorescent in solution but they could emit strong light when aggregated in solid films or gathered into nanoparticles, demonstrating an intriguing phenomenon of aggregation-induced emission(AIE). This phenomenon is contrast to phenomenon of aggregation-caused quenching(ACQ), providing a new method to alleviate difficult ACQ problem.Siloles are typical AIE-active molecules. Scientific workers have made extensive researches on the design, synthesis, structure, properties and application of siloles,and found that they can be widely used in optoelectronic devices, biological probes,chemical sensors, and so on. The functionalization of siloles is still a hot research topic, which will provide functional materials with potential applications. This article will focus on the modification of siloles at 2,5-positions of silole ring, by introducing different functional groups. We synthesized and characterized a series of silole derivatives, and studied their properties and applications in organic light-emitting diodes(OLEDs), biological imaging and so on.First, we designed and synthesized three siloles derivatives by introducing9,9-dimethylfluorenyl, carbazole, dimesitylboryl and diphenylphosphine oxide substituents at the 2,5-positions of silole rings. The obtained three new silole derivatives,(MesBF)2MTPS,(DPPOF)2MTPS and(MesBC)2MTPS, showed low LUMO energy levels. By adopting them as light-emitting layer or electron transporting and light-emiting layers, we fabricated the non-doped OLEDs, and investigated the device performance. The results showed that(MesBF)2MTPS was a good light-emitting material, and its device exhibited the high EL performance(48348cd/m2, 12.26 cd/A, 8.82 lm/W and 4.11%).Second, by introducing the fluorene groups containing alkyl chains into silole molecules, we synthesized two bulky silole derivatives, Silole-SF and Silole-SFE.The siloles derivatives had aggregation-enhanced emission features, high thermal stability and excellent film-forming properties. They could be used as light emitters to fabricate the nondoped OLEDs by solution-processing technique. The electroluminescence properties of the devices were investigated, and the results showed that(MesBF)2MTPS possessed the better electroluminescence performances,which afforded current efficiency, and external quantum efficiency of 3.0 cd/A, and1%, respectively.Finally, by introducing the thiophene groups at the 2,5-positions of siloles to increase the molecular conjugation length, we synthesized a positively charged fluorescent dye, Silole-SNBr. The fluorescent emission wavelength was 567 nm,when dissolved in dimethyl sulfoxide(DMSO), and its fluorescence quantum yield was up 22%. In addition, the fluorescent dye can stain the cytoplasm of Hela and MCF-7 cell. When the concentration of the dye was set at 30 microns and the staning time was one hour, best fluorescence imaging effect of cytoplasm was achieved.