New Aggregation-induced Emission Luminogens: Synthesis And Applications In Optoelectric Devices And Bioimaging

Organic semiconductor materials have become one of the hotspots in advanced functional materials in the 21^st century.As one of the most studied organic semiconductor materials,organic light-emitting materials attracted widespread attention due to their tremendous utility in the field of organic light-emitting diodes?OLEDs?,organic light-emitting transistors,organic lasers and chemosensors and bioprobes.However,most conventional organic light-emitting materials suffer serious aggregation-caused quenching?ACQ?effect in the aggregate state,which has limited the practical applications of organic light-emitting materials.Aggregation-induced emission?AIE?,firstly coined by Professor Ben Zhong Tang in 2001,is currently recognized as the most effective way to overcome ACQ problem and has developed into a new area that is spearheaded by Chinese scientists and has developed into a frontier research in the field of chemistry.However,there are still some unsolved basic scientific problems and challenges,such as how to understand the relevant mechanism and establish theory model and design principle,and how to develop the applications of obtained AIE materials.The key directions are preparation of novel AIE molecules and development of applications of AIE materials in optoelectronic devices and bioimaging.In Chapters 2 and 3,we designed and synthesized a series of novel single-molecule wires featuring AIE and through-space conjugated hexaphenylbenze and proposed the multichannel conductance model.Compared to traditional through-bond single-molecule wires,the multichannel conductance single-molecule wires featuring through-bond conjugation and through-space conjugation can effectively improve the conductance of single-molecule wires.The multichannel channel single-molecule wires exhibits higher conductance by more than several times compared with its liner counterpart.At the same time,the introduction of methoxyl groups can not only increase the degree of through-space conjugation,but also can effectively improve the conductance of single-molecule wires.In addition,the effect of different anchor groups on the electrical transport properties of single-molecule wires was also investigated.This multichannel single-molecule wires also provide a novel model for understanding the redox process of biological complex systems and the transfer of charge in DNA and optoelectronic devices.In Chapters 4,we obtained a series of novel single-molecule wires with AIE and through-space conjugation by introducing thiophene into hexaphenlybenze.They are used to construct metal-molecule-metal junctions.The introduction of thiophene not only increase the electronic cloud density and degree of through-space conjugation,but also improve the conductance of single-molecule wires.Compared to single-molecule wires based on hexaphenylbenze,this kind of single-molecule wires based on hexaarylbenzene derivatives can effectively improve the conductance of single-molecule wires.This work provides an effective way for designing high-conductance single-molecule wires.In Chapters 5,two family of luminogens featuring AIE based on phosphindole oxide?PIO?and benzo[b]thiophene S,S-dioxide?BTO?cores and thiophene substituents are prepared and fully characterized.Their structures and optical properties are comparatively investigated by crystallography,spectroscopy,theory calculation,etc.These luminogens with different connection patterns between thiophene and PIO/BTO cores exhibit different torsion angles and thus diverse photophysical properties.The luminogens show faint emissions in solutions but enhanced emissions in the aggregated state,displaying good AIE feature.Reversible photochromism is observed for the luminogens,and the PIO-based luminogens show better photochromism property than BTO-based ones.The interesting photoluminescence and photochromism properties endow these new luminogens with good potential in optoelectronic devices and molecular switches.In Chapters 6 and 7,in order to develop the AIE system base on BTO,we designed and synthesized a novel AIE core,benzo[1,2-b:4,5-b']dithiophene 1,1,5,5-tetraoxide?BDTO?,which reveals strong electron-withdrawing properties.By introducing different donor groups,we obtained a series of luminogens with diverse emission.Crystallographic,spectroscopic,electrochemical and computational results reveal that the dyes based on BDTO can endow the fluorophores with enhanced emission efficiency,enlarged two-photon absorption cross section and increased reactive oxygen species generation efficiency.They also show good electroluminescent properties in the solution-processed nondoped OLEDs.By utilizing these luminogens as the light-emitting layer,we constructed a series of solution-processed non-doped OLEDs,whose EL efficiency is optimized to 13092 cd m^-2,19.67 cd A^-1 and 5.83%.In Chapters 8,a series of red/near-infrared fluorophores based on BDTO are synthesized and characterized.They possess both aggregation-induced emission and hybridized local and charge-transfer characteristics.Crystallographic,spectroscopic,electrochemical and computational results reveal that the oxidation of benzo[1,2-b:4,5-b']dithiophene to electron-withdrawing BDTO can endow the fluorophores with greatly red-shifted emission,enhanced emission efficiency,reduced energy levels,enlarged two-photon absorption cross section and increased reactive oxygen species generation efficiency.The nanoparticles fabricated with a near-infrared fluorophore TPA-BDTO show high photostability and biocompatibility with good performance in targeted photodynamic ablation of cancer cells and two-photon fluorescence imaging of intravital mouse brain vasculature.