Tetraphenylethene-Decorated BODIPY Fluorescent Dyes And Novel Luminescent Materials From Siloles: Design, Synthesis And Application

Aggregation-induced emission(AIE) phenomenon was reported by Tang’s group in 2001. It refers to a series of propeller-like luminogens that are non-fluorescent in solutions but emit strongly by aggregate formation, which is completely opposite to the aggregation-caused quenching(ACQ) phenomenon encountered by conventional planar fluorescent chromophores(PFCs). This important finding paves a new avenue to alleviate the ACQ problem. AIE phenomenon has been discovered in certain kinds of molecules, such as tetraphenylethenes, siloles, etc. These AIE-active luminogenic materials show great potential in chemosensors, fluorescent bioprobes, organic light-emitting diodes(OLEDs), etc.In this thesis, tetraphenylethene-decorated BODIPY luminogens are synthesized and used in two-photon excited fluorescence cellular imaging and mouse brain blood vascular visualization. 2,5-Difluorenyl or PFCs-substituted siloles are also synthesized, in order to fabricate high-performance OLEDs and understand the structure-properties relationships of luminescent materials. The specific contents are as follows:(1) Three TPE-BODIPY adducts are synthesized and characterized, and their photophysical properties and electronic structures are investigated. The incorporation of AIE-active TPE units alleviates aggregation-caused quenching of BODIPY core, furnishing emissive nanoparticles based on TPE-BODIPY adducts. Significantly, the two-photon absorption(TPA) and two-photon excited fluorescence(TPEF) properties are improved as more TPE units are incorporated. The luminogens with 3TPE units(3TPE-BODIPY) shows the strongest TPA and TPEF in the wavelength range of 750–830 nm, with cross section values of 264 and 116 GM at 810 nm, respectively. Red emissive nanoparticles with a Stokes shift of 60 nm and a fluorescence quantum yield(?F) of 16% are attained by encapsulating 3TPE-BODIPY with 1,2-sistearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000]. The nanoparticles are biocompatible and function well in two-photon excited fluorescence imagings of cells and blood vessels.(2) Bulky substituents of 9,9-dimethylfluorene, 9,9-diphenylfluorene, or 9,9’-spirobifluorene are successfully introduced into the 2,5-positions of silole rings. The generated 2,5-difluorenyl-substituted siloles are thermally stable, and possess low-lying LUMO energy levels. The crystallograhic analysis reveals that intramolecular π–π interactions are prone to form between 9,9’-spirobifluorene units and phenyl rings at the 3,4-positions of silole ring. In the solution state, these new siloles show weak blue and green emission bands, arising from the fluorenyl groups and silole rings with certain extension of π–conjugation, respectively. When the substituent volume is increased, the intramolecular rotation is reduced, and thus the emissions of the siloles are improved gradually, affording higher ?F values of 2.5–5.4% than those of 2,3,4,5-tetraphenylsiloles. They are highly emissive in solid films with dominative green to yellow emissions and good solid-state ?F values of 75–88%, presenting an aggregation-enhanced emission(AEE) characteristic. Efficient OLEDs are fabricated by adopting them as host emitters, which give high luminance, current and power efficiencies up to 44100 cd/m2, 18.3 cd/A and 15.7 lm/W, respectively. In particular, a noticeable maximum external quantum efficiency of 5.5% is achieved in an optimized device, which exceeds the theory limite of the electroluminescence devices.(3) A series of new siloles carrying planar fluorescent chromophores(PFCs) at the 2,5-positions, including fluorene, fluoranthene, naphthalene, pyrene and anthracene, are synthesized and characterized. Their emissions in the solution state are weak, due to active intramolecular rotation(IMR), but the synergistic effect from the electronic coupling between PFC and silole ring compensates the emission quenching by the IMR process in some measurement, affording higher emission efficiencies than those of 2,3,4,5-tetraphenylsiloles in solutions. The new siloles show enhanced emission efficiencies when they exist in the aggregated state. The electroluminescence(EL) color and efficiency of them are sensitive to PFCs. The siloles with naphthalenes show green EL emission, while those with anthracenes show orange EL emission. The siloles with pyrenes exhibit yellow EL emission at 546 nm, with a peak luminance of 49000 cd/cm2, and a high current efficiency of 9.1 cd/A.