New Organic Fluorescent Materials With Aggregation-induced Emission Characteristics: Synthesis,Applications And Narrow Band-gap Conjugated Small Molecules: Synthesis,Properties Investigation

In 2001,a novel phenomenon of aggregation-induced emission?AIE?was first found by Tang's group.This has attracted considerable research attention and more and more research groups embark on the studies of the AIE mechanism and applications.AIE materials have found diverse potential applications in OLED,chemosensors,bioimaging,etc.In this article,new AIE molecules were synthesized and investigated.In particular,red emission AIE molecules was synthesized and applied in biological imaging.In recent years,organic solar cells have become a hot research for the low cost,easy modification.In many solar cell materials,D-A system with wide absorption and appropriate level have become the main system.The diketopyrrolopyrrole?DPP?with being coplanarity and strong acceptor has attracted much attention.And in this article,a family of narrow-band gap?-conjugated small molecules based on diketopyrrolopyrrole as core has been successfully synthesized and investigated the relationship between properties and structure.The details are as follows:?1?In the first section,two rigid,multiple tetraphenylethene?TPE?substituted,?-conjugated,snowflake-shaped luminophores BT and BPT were facilely synthesized by 6-fold Suzuki coupling reaction.These molecules are constructed based on the nonplanar structure of propeller-shaped Hexaphenylbenzene?HPB?or benzene as core groups and TPE as end groups.As a result,they reserve the intrinsic aggregation-induced emission?AIE?property of the TPE moiety.They showed much stronger AIE effect and higher?_F,f in the solid state 66%and 43%,?_AIEIE about 154and 206.These results indicated that the steric repulsion and conformation has a significantly influence on the AIE effect.Numerous regular microscale fibers with uniform microrod or microbelt shapes was observed.An excellent optical waveguide application of these molecules was achieved.The optical loss coefficient of the microwires was calculated to be about 0.030,0.028 dB?m^-1,respectively.Meanwhile,piezochromic behaviour in the solid state can be tuned or switched by inserting the phenyl bridges through changing the twisting conformation.The emission spectrum of the ground powder exhibited a large red shift of 30 nm due to different solid states.Further investigation showed that this reversible fluorescence change can be cycled for many times via alternating operation with grinding and solvent treatment.However,the piezofluorochromic behavior has not appeared when BPT was ground using a pestle.?2?In the second part,we design and synthesize the same diphenylamine terminal group and the same four branched core,2,2-?2,2-diphenylethene-1,1-diyl?dithiophene,which showed stronger electron-donating ability and easier modification than TPE unit.To modulate the donor-acceptor interaction and get red emission TPABT,DTPABT,TPEBT and DTPEBT,TPE or triphenylamine mono-functionalized benzo[c][1,2,5]thiadiazole?BT?was employed as the other terminal group.In particular,the thin film of materials exhibited the highest fluorescent quantum efficiency of ca.38%with the highest?_AIE.The cell viability remains above 85%within 36 h under the experimental conditions,indicating the low cytotoxicity of the molecules.Moreover,with TPE groups showed very large two-photon absorption cross-section 1.94×10³ GM at 780 nm,which is obvious higher than the other red fluorescent materials with triphenylamine groups.Then,the one-photon and two-photon fluorescence imaging of MCF-7 breast cancer cells,Hela cells were carried out with these red fluorescent materials.Intense intracellular red fluorescence was observed from all the molecules by one-photon excited and from TPABT by two-photon excited in the cell cytoplasm.Finally,the materials are biocompatible and function well in mouse brain blood vascular visualization.?3?In the last section,a family of narrow-band gap?-conjugated small molecules based on diketopyrrolopyrrole as core with oligothiophene or thiazole ring have been successfully synthesized.They exhibited intensive absorption bands?300⁹00 nm?and deep-lying HOMO energy levels?-5.41^-5.60 eV?due to donor-acceptor interaction and multiple fluorine substituents.We inserted two thiophene between the DPP and benzothiadiazole,it exhibited good liquid crystal behavior with Smectic phase.However,we did not observe such behaviours in DTFB2T.These changes of characteristics make us realize that subtle changes in the regulatory structure can bring great change in absorption,energy and morphology of molecules,which will affect the PCE of solar cells.