Design,synthesis And Applications Of Force/photo-responsive Fluorescent Molecules

Stimuli-responsive materials are a new type of functional materials that can respond to external stimuli such as force,light,humidity,temperature and pH.They are widely used in chemical sensors,anti-counterfeiting,optoelectronic data storage,biomedicine and other fields.The responsive mechanism is related to intermolecular interactions,intramolecular conformation and chemical structure.However,due to the phenomenon of aggregation induced fluorescence quenching,the stimuli-responsive behavior of these dye molecules is limited in the aggregation state,which greatly limits the application range of materials.Thus,it will be an innovative and challenging subject to realize the efficient stimuli-responsive ability in solid state by appropriate molecular design,to expand their application scope.In this paper,triphenylamine,phenothiazine and spiropyran dye molecules were optimized to synthesize a series of compounds that responded to force/light in the aggregation state.Together with theoretical simulation and properties characterization,the relationship between molecular structure,molecular aggregation and material properties was revealed.The research contents are as follows:1.To explore the relationship between molecular stacking structure and luminescence performance.We design and synthesis benzothiazole functionalized triphenylamine molecule.Triphenylamine acts as electron donor and benzothiazole acts as electron acceptor,which are beneficial to intramolecular charge transfer in excited state.In addition,triphenylamine has a twisted conformation,preventing the compact aggregation in solid state,which can improve fluorescence quantum yield in solid state.The polymorphs of blue emission(TZ-1B)and cyan emission(TZ-1C)crystals are obtained in controlling the crystallization conditions.By molecular systems and detailed single crystals analyse,it is found that appropriate substituent plays a key role in manipulating the intermolecular interactions and the molecular packing modes to affect the optical properties of organic crystals.Moreover,TZ-1C exhibits blue-shift mechanochromism,while TZ-1B does not.More importantly,TZ-1B exhibits lasing emission at 454 nm with low threshold and high cavity quality factor.TZ-1C exhibits amplified spontaneous emission(ASE)at 462 nm.Thus,the molecular systems provide a reasonably potent to understand molecular packing structure-fluorescent property relationship2.We design and synthesize the compound(PTZ-BZ)with multicolored mechanochromic switching by changing conformation of phenothiazine.PTZ-BZ is a D-?-A type molecule with twisted structure,facilitating modulation of molecular interactions and conformations for aggregation-induced emission and mechanochromic properties.We obtained blue-green emission crystals,peaking at 475 nm in mixed solvent(methanol:dichloromethane=1:1).Dimers are formed between adjacent two molecules by multiple intermolecular interactions.Once the crystallinity collapses,PTZ-BZ crystals exhibit obvious blue-shifted mechanochromism.Further grinding,red-shifted mechanochromic behavior is obtained.To deeply figure out the relationships between multicolored mechanochromism properties and the changes of structure,various photophysical characterizations,powder X-ray diffraction,and single-crystal analyses were implemented.The relationships between the multicolored mechanochromic properties of PTZ-BZ crystals and different intermolecular interactions and intramolecular conformation are revealed.This study will provide a reliable strategy to tune the mechanochromic emission wavelengths by modulating twisted molecular conformations and weak intermolecular interactions,indicating its underlying applications in optical anti-counterfeiting materials.3.To realize solid state spiropyrane's photochromism,TPE-SP was designed and synthesized by covalent modification of benzothiazole functionalized tetraphenylethene with spiropyran molecule through esterification reaction.Benzothiazole functionalized tetraphenylethylene(TPE-OH)moiety with a highly twisted conformation provides a large free volume to facilitate the photoisomerization process of spiropyrane(SP)and enhance NIR emission of merocyanine with a high qutumn yield of 11.2%in the solid state.TPE-SP aggregates exhibit obvious photochromism under UV irradiation,in which the visible color changes from pale yellow to blue,and the fluorescent color changes from green to red.Moreover,self-assembled TPE-SP microsphercial caps simultaneously serve as gain media and resonating microcavities,providing optical gain and feedback for NIR laser oscillations with a low threshold(3.68 ?J/cm2).These results are beneficial for deeply understanding the SP microstructures-lasing emission characteristic relationship and provide a useful guideline for the rational molecular design of NIR microlasers with special functionalities.