Anthracene-based Nitro Aggregation-Induced Emission System

Organic luminescent materials are widely used in biological and chemical sensing,fluorescence probes,optoelectronic systems and stimuli-responsive materials.However,in the view of practical application,the traditional aggregation-caused quenching(ACQ)effect is generally considered to be unfavorable.Various chemical,physical and engineering approaches and processes have been taken to solve the problems caused by the ACQ effect,but none of them can solve the problem perfectly.A novel phenomenon of aggregation-induced emission(AIE)was discovered and reported.Materials with AIE characteristics do not emit light in solution state,but become highly fluorescent in the aggregated state.In sharp contrast with the ACQ effect,the AIE phenomenon has both academic research significance and practical application significance,and thus attracted dozens of research groups from around the world to participate in the related research of the development and exploration of the novel AIE system and investigation of its working mechanism and applications.Anthracene is a typical ACQ luminophore with largeπconjugated rigid planar molecular structure.It has been proven that ACQ fluorophores can be changed to AIE fluorophores by introducing functional groups that can undergo effective motion and increasing non-planarity to the ACQ fluorophore.The nitro group is believed to exert strong quenching effect on the fluorescence emission,so it is expected that fluorophores with nitro group will fluoresce weakly both in solution and solid state,making it difficult to construct an AIE system.On the other hand,molecules with nitro group are usually easy to synthesize and purify,and their starting materials are cheap.In this sense,introducing nitro group to AIE systems is of great significance to the mass production of AIE materials.In this thesis,we focus on the research hotspot of AIE fluorophores with fluorescence-quenching nitro group substituents,to design and develop a nitro-group-based luminescent system with AIE properties.Taking advantage of anthracene as the aromatic skeleton,we introduced a rotatable benzene ring as a bridging group to construct a new system with highly emissive chromophore and fluorescence-quenching nitro group.We investigated the feasibility of converting ACQ luminophore into an AIE luminogen to prepare a nitroaromatic system with AIE features.In this thesis,a series of nitroaromatic compounds with anthracene skeleton and nitro group substitution at different position were designed and synthesized.Their chemical structure,thermal stability,purity and crystal structure were characterized by nuclear magnetic resonance hydrogen spectroscopy(~1H NMR),thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC),high resolution mass spectrometry(HRMS)and single crystal analysis,respectively,while their photophysical properties,such as fluorescence spectra,UV-Vis absorption spectra and fluorescence quantum yield were also measured in different states.By a systematical analysis of their photophysical properties in the solution and solid state,the role of nitro group at different substitution position was investigated,and the structure-property relationship was built.By taking account of the two quenching fluorescence pathways of the nitro group and the twisted intramolecular charge transfer(TICT)process,the mechanism of the nitro group affecting the decay pathway of the excited state in solution and solid state is uncovered.