Emission-tunable Tetraphenylethene Derivatives:Synthesis And Applications In OLEDs And Bioimaging

organic luminescent materials possess many merits,such as diverse structures,tunable emission wavelength,excellent luminescent properties,and have shown great potential applications in organic optoelectronic devices,chemical sensors,biological probes and fluorescence imaging,and so on.Most conventional luminophores are strongly emissive in dilute solutions,but they glow a rather weak light or even go dark in the aggregated state.This aggregation-caused quenching(ACQ)effect has become a thorny obstacle of their practical applications.Fortunately,the luminogenic molecules that feature a distinctive photophysical process of aggregation-induced emission(AIE)can behavior against ACQ materials,and radiate rather stronger emission in aggregated states than in dilute solutions,which perfectly satisfy their practical applications and provide a valid molecular design strategy to construct highly efficient solid-state luminescent materials.Tetraphenylethene(TPE)is one of the most popular AIE units.It has a simple molecular structure but superb AIE attribute,and can be modified facilely to construct highly efficient solid-state luminescent materials.In this thesis,a series of TPE derivatives with different emission colors were synthesized.Their applications in organic light-emitting diodes(OLEDs)and bioimaging were investigated.In chapter 2,two linear TPE derivatives(TPE-TPAPBI and TPE-DPBI)that are functionalized with hole-transporting triphenylamine and/or electron-transporting 1,2-diphenyl-1H-benzimidazole groups were synthesized and characterized.They had excellent photoluminescence quantum yields approaching 100% in vacuum deposited films and high electron-transporting ability.The electron mobility of TPE-TPAPBI and TPE-DPBI were comparable or even superior to that of 1,3,5-tri(1-phenylbenzimidazol-2-yl)benzene(TPBi).The nondoped OLED device employing TPE-TPAPBI as active layer emitted green light,affording ultrahigh luminance of 125300 cd m-2,and excellent maximum current,power and external quantum efficiencies of up to 16.8 cd A-1,14.6 lm W-1 and 5.8%,respectively,with very small roll-offs,demonstrating that TPE-TPAPBI is a highly promising luminescent material for nondoped OLEDs.In chapter 3,a TPE derivative TPE-FB was synthesized by decorating TPE with electron-transporting dimesitylboryl and thermally stable fluorene groups.TPE-FB emitted sky-blue light at 481 nm with a high photoluminescence quantum yield of 64% in solid film.The combination of fluorene and dimesitylboryl groups improves the thermal stability of the materials and the decomposition temperature of TPE-FB was higher than other dimesitylboryl-including TPE derivatives previously reported.The nondoped OLED device based on TPE-FB show a turn-on voltage of 4.3 V,and a maximum external quantum efficiency of 1.78%.In chapter 4,red luminescent materials,PITBT-TPE and t-BPITBT-TPE,comprised of TPE,2,1,3-benzothiadiazole,thiophene and 9,10-phenanthroimidazole were synthesized.The addition of tert-butyl increased the photoluminescence quantum yield from 24% of PITBT-TPE to 49% of t-BPITBT-TPE.The nondoped OLED based on t-BPITBT-TPE emitted pure red light,with electroluminescence peak of 650 nm and CIE of(0.666,0.333).The turn-on voltage of the device was as low as 2.5 V,and the maximum external quantum efficiency was up to 2.17%.Nanoparticles were fabricated by encapsulating t-BPITBT-TPE in polymeric micelles via nanoprecipitation.Modification with different terminal functional groups yielded nanoparticles with different surface charges.In vivo zebrafish analysis suggested that NH2-TAT nanoparticles with positive surface charges had the lowest toxicity and the best cellular penetrability.HeLa and MCF-7 cells tagged with NH2-TAT nanoparticles were xenografted into zebrafish larvae and successfully tracked the dynamic cancer cell proliferation and metastasis.