Design,Synthesis And Applications Of Diarylethene Photochromic Materials With Aggregation-Induced Emission

Photochromic molecules are a class of materials that are stimulated by light.Under a certain wavelength of light radiation,the molecule undergoes a structural change that brings about a change in its absorption wavelength and various properties,and then returns to its original structure under heat or another wavelength of light radiation.Due to the excellent performance of diarylethylenes(DAEs)photochromic molecules,especially fatigue resistance and high stability of the isomers,their applications in information storage,molecular switching,anti-counterfeiting and bioimaging are developing rapidly.However,DAEs often suffer from the notorious phenomenon of aggregation-caused quenching(ACQ),which can lead to significant weakening or quenching of fluorescence in the aggregated state and severely restrict their range of application.In 2001,the concept of aggregation-induced emission(AIE)proposed by Tang’s team,which is opposite to the ACQ effect,with weak or no fluorescence in solution and strong fluorescence in the solid or aggregated state.This provides an excellent strategy to address the limitations faced by photochromic molecules.As a result,photochromic molecules with aggregation-induced emission(AIE)properties are receiving increasing attention for their bright fluorescence in the solid state and their ability to modulate structural and physicochemical properties under light stimulation.In this thesis,a novel molecular system design strategy is proposed to integrate the colour-changing unit and the AIE unit in one molecule,and a series of diarylethylene photochromic molecules with aggregation-induced luminescence are successfully designed and synthesized.The main research contents are as follows:(1)By introducing photoactive furan or benzofuran groups into the skeleton of AIE-active triphenylethylene molecules,the molecules have a unique photophysical behaviour of aggregation-induced emission and interesting photochromic activity.These molecules undergo cyclisation under UV irradiation and the cyclisation products are experimentally and theoretically confirmed to be predominantly E-type.Excellent reversible photochromic behaviour was observed in the solid,solution and film states,and the position and conjugation of the furan moiety had a significant effect on the colour and intensity of the photochromic.These reversible photochromic molecular switches with dual-channel changes have a dual output mode of light-convertible absorption and fluorescence.It is therefore applied to photoswitchable patterning on a filter paper and anti-counterfeiting of an anti-falsification paper to reveal its potential in the field of information storage and anti-counterfeiting.(2)Through rational molecular design,light-activated turn-on mode fluorescence compound with AIE properties was successfully obtained by introducing pyridine groups into the diarylethylene system and further transforming it into a methylpyridinium salt.Both of them are AIEgens and are photochemically active.Their photochromic properties,aggregation-induced emission properties and photoactivated fluorescence behaviour were investigated.The experimental data results show that the introduction of positive ions reduces the aromaticity of the pyridine ring,which makes the diarylethylene system more susceptible to cyclisation dehydrogenation,and then activating the fluorescence of the solution.To further explore the occurrence of the cyclisation dehydrogenation reaction,~1H NMR spectra before and after UV irradiation were compared.The molecule was applied to a light-controlled graph in the film state to confirm their potential application for information storage.The colour changes of the film before and after UV irradiation were not significant,but the changes of fluorescence were obviously,which suggested that it could be potentially served as an anti-counterfeiting material.