Synthesis And Properties Research Of Diarylethene Fluorescence Molecular Switch With Aggregation-induced Emissions Effect

Diarylethylene is an important class of organic photochromic compounds,and it has attracted wide attention due to its excellent fatigue resistance and thermal stability.Currently,many diarylethene fluorescent molecular switches have been designed and synthesized,they are widely used in information storage,imaging and other fields.However,their fluorescence signals are often affected by the "concentration quenching" effect,which severely limits their practical applications.Therefore,this paper proposes to construct a diarylethene molecular switching system with AIE properties by introducing tetraarylethene-based aggregation-induced emission(AIE)groups,and a series of novel diarylethene fluorescent molecular switches have been designed and synthesized.Their photochromic and fluorescence switching performance in different media were studied,and the applications in the field of optical storage and super resolution imaging were explored.The main research contents are as follows:(1)Two novel small molecule fluorescent switches TPE-2DTE and OTPE-2DTE were prepared by modifying the single tetraarylethylene(tetraphenylethylene TPE or containing oxygen bridge tetraphenylethylene OTPE)groups with bis-diarylethene(DTE).Their open-form isomers exhibit typical AIE effects,that is,the fluorescence is weak in good solvent,but enhanced dramatically in the aggregated or solid state.TPE-2DTE and OTPE-2DTE can undergo obvious photoisomerization reaction under irradiation of light below 405 nm.At the same time,the fluorescence is quickly quenched.The critical response wavelength is approximately 450 nm,and the inverse process takes place under irradiation of long wavelength visible light with the fluorescence completely restored.Their fatigue resistance is good.In particular,the maximum on/off fluorescence ratio is higher than 1000 : 1 under irradiation of 405 nm light which is the highest value obtained so far for the diarylethene molecules with AIE effect under visible light irradiation.Utilizing their excellent switching performance under visible light,macro-pattern rewritable models have been demonstrated and super resolution images with the resolution below 60 nm have been achieved.(2)A kind of tetraphenylethylene-dithienylethylene alternating conjugated oligomer 3TPE-2DTE was designed and synthesized.The fluorescence intensity of the molecule in the aggregated state was 46 times stronger than that in the solution state.After being irradiated with 365 nm UV light for 2 s,the enhanced fluorescence is effectively quenched by the resulting ring-closed isomer,and ring-closed reaction's conversion rate in the photostationary state is as high as 95%.The maximum fluorescence on/off ratio can reach 3676 : 1.Tetraphenylethylene not only brings AIE effect,but also acts as an electron-donating conjugation structure which effectively increases the degree of conjugation of the entire molecule,making the 3TPE-2DTE molecule undergo highly efficient and rapid photochromic reaction under 400 ~ 420 nm light irradiation.What's more,it can obtain a ring-closed conversion yield of 68% under 405 nm light irradiation.Utilizing the excellent switching performance of 3TPE-2DTE,a millimeter-scale rewritable model has been demonstrated,and a super resolution image with a resolution below 50 nm have been achieved.(3)Two kinds of tetraarylethylene-dithienylethylene alternating conjugated polymers Poly(TPE-DTE)and Poly(OTPE-DTE)with different fluorescence emission wavelengths were designed and synthesized.They are sensitive to ultraviolet light and visible light at 405 nm with both having high conversion rates.They exhibit typical AIE effects.In the poor solvent and rigid polymer media,the fluorescence quenching rate is greatly improved compared to the oligomer 3TPE-2DTE.The fluorescence peak of the Poly(OTPE-DTE)is located at 606 nm,which almost completely overlaps with the absorption peak of the closed-form DTE.As a result,the energy transfer of Poly(OTPE-DTE)can be performed more efficiently.Good fatigue resistance and good response to the 405 nm visible light enable Poly(TPE-DTE)and Poly(OTPE-DTE)to achieve super resolution images with the entire resolutions of 44 nm and 63 nm respectively which are co-regulated by the 405 nm and 561 nm light.They have potential value in practical applications such as imaging or information storage.