Synthesis And Application Of Aggregation-induced Emission Materials With Mechanoluminescence And Photo-induced Fluorescence Enhancement

Compared with inorganic luminescent materials,organic materials enjoy a series of advantages such as emission color tunability,low cost and diversified structures,which have attracted much attention from scientists.However,conventional organic luminescent materials often suffer from π-π stacking interaction in solid state,which cause the emission quenching of the molecules,limiting the real application of the materials.On the contrary,aggregation-induced emission(AIE)compounds are non-emissive or faintly emissive in solution,but greatly enhanced emission in aggregated or solid state.Mechanical force is usually applied in solid state or aggregated state for mechanoluminescent materials,which requires efficient aggregated state emission of the compounds.Based on these aspects,this thesis investigated two types of new AIE compounds: mechanoluminescent indole derivatives and tetraphenylethene derivatives with photo-induced fluorescence enhancement.Firstly,ten indole derivatives were designed and synthesized based on the emission mechanism of AIE.Oxindole is designed as the core structure,and two free rotatable phenyl rings are introduced on the core.The free rotation of the benzene ring dissipates the excited state energy in solution,while these movements are hindered in solid state,endowing the compounds with AIE characteristics.Through introduction of different substitution groups with electron donating/withdrawing properties on the phenyl rings,the modulation of the emission color can be realized.The analysis of the single crystal structures of these ten compounds suggests that most of the compounds form dimer or trimer in their crystal structures through intermolecular hydrogen bonds.Besides,there are two uncentrosymmetrical crystals and their molecules form a pair of helical chain structure with opposite helicity in their crystals through head-to-tail intermolecular hydrogen bond.They both show mechanoluminescence.Upon grinding the two crystals,obvious yellow emission at about 580 nm can be observed in the dark.For one of the compound,through simple heating above its melting point and sudden cooling in liquid nitrogen,crystal with mechanoluminescence behavior can be easily obtained.This method is simple and repeatable,which provide a convenient method for the preparation of mechanoluminescent materials.Secondly,a series of sulfur-containing tetraphenylethene derivatives with photo-induced fluorescence enhancement were synthesized by one-pot two-step tandem reaction.Through the analysis of NMR,IR and single crystal structure,the C=C bonds in these compounds are mainly Z-configuration.The solution and aggregated states of these compounds are all non-emissive or faintly emissive.Their solid powder or thin film show enhanced red emission upon irradiation by UV light.When the sulfur atom was oxidized to sulfonyl group,they transfer to the aggregation-induced emission materials.We then systematically investigated the underlying mechanism for the photo-induced fluorescence enhancement and photo-induced red emission of these sulfur-containing or sulfonyl group-containing tetraphenylethene compounds and proposed that photo-induced cyclization reaction might take place to produce red emissive species.