Design,Synthesis And Property Of Spiropyran-based Solid State Fluorescent Photoswitch

Solid-state fluorescent photoswitches can realize reversible switching in color,fluorescence intensity,and fluorescence color under the stimulation of specific wavelengths of light.In recent years,solid-state fluorescent photoswitches have drawn researchers’ attention because such materials exhibited excellent application value in the fields of anti-counterfeiting coatings,optical information storage medium,bioimaging fluorescent probes and super-resolution imaging dyes.The researches on spiropyran(SP)-based solid-state fluorescent photoswitching materials have made some remarkable progress,but the molecular arrangement and intermolecular interactions in solid state are complex,and the uncontrollable aggregated molecular structure will lead to unstable photoisomerization process and luminescence properties.Therefore,there is still a lack of effective molecular design strategies.In addition,developing new material systems for solid-state fluorescent photoswitches,recognizing and understanding the relationship between molecular aggregate structure and luminescence properties,and exploring new functions are of great significance for the development and application of SP-based solid-state fluorescent photoswitches.Herein,the materials in my doctoral thesis are all based on the SP photoswitches,and by modifying different groups to the nitrogen atom on the indoline ring of SP,such as ester bond,amide bond,alkyl chain,tetraphenylethylene(TPE)derivatives and 9,10-distyrylanthrance(DSA)derivative,etc.,we designed and synthesized a variety of new solid-state fluorescent photoswitches.We explored the internal relationship among molecular structure,aggregate state structure and photoresponsive fluorescence switching property,and explored the practical application scenarios of solid-state SP-based fluorescent photoswitching materials.Main contents:1.Seven SP derivatives were designed and synthesized with different types of flexible chain groups.Among them,1-SP,2-SP,3-SP,4-SP,5-SP and 6-SP,the derivatives of flexible chain attached to the indoline ring of SP,successfully exhibited solid-state single red fluorescence reversible switching properties.However,the derivative 7-SP in which the flexible chain was attached to the benzopyran ring of SP did not exhibit the fluorescence switching property in the aggregated state,but also lacks this property in the single molecule state.Detailed crystalline structure and theoretical studies revealed that these flexible chain not only increased the intermolecular distance of the merocyanine(MC)and SP moieties in the solid state,created a large intermolecular space for the reversible photoisomerization of SP in solid state,but also effectively weakened the intermolecular interaction,reduced the limitations to the photoisomerization of SP.However,attaching the flexible chain to the benzopyran ring of SP will change the thermal stability of the open/closed ring configuration of SP,making it completely lose the photoisomerization property.2.By connecting SP with TPE derivatives with aggregation induced emission properties through a flexible ester chain,we report reversible dual fluorescent photoswitching characteristics in the solid state of SP-functionalized TPE derivatives,TPEA-SP and TPEB-SP.These photoswitches exhibit two distinct and selectively addressable states,a cyan fluorescence and a red fluorescence,which can be conveyed into each other in a reversible feature upon irradiation with alternating UV and visible light.Detailed spectroscopic and theoretical studies suggest that the cyan fluorescence of the initial closed-ring state should arise from the localized excited state of TPE moiety and the intramolecular energy transfer process from TPE to merocyanine(MC)leads to the switching from cyan to red fluorescence of the open-ring state.Moreover,the nonplanar molecular conformation of TPE and ester chain moieties lead to large free volumes,which facilitates the reversible photoisomerization of SP.The excellent reversibility and high-contrast fluorescence of solid-state photoswitches enable great applications in anticounterfeiting inks and aggregated state optical information storage medium.3.By connecting SP with DSA derivative with two-photon absorption properties through a flexible ester chain,we develop a novel solid-state fluorescence photoswitch,BOSA-SP.By performing "Pump light(488/800/950 nm)" to excite stable photoluminescence of the fluorogen moiety;performing "Trigger light(405/524/800 nm)" to regulate photoisomerization of SP moiety,we firstly realized the controllable and reversible triple fluorescence switching in a single solid-state organic photoswitch system.Owing to these fancy properties,BOSA-SP prospectively has multiple applications in various fields,such as three-color tunable switching cellular imaging and two-color super-resolution imaging.