Construction And Application Of Reversible Supramolecular Optical Chemosensors Based On Host-guest Interactions(supported By Nscf,no.21904040;shanghai Pujiang Project,no.19pj1402800)

Optical chemosensors are effective tools for rapid and accurate monitoring chemical information of target analytes and sensing the microscopic world.In terms of the sensing mechanism,optical chemosensors can be divided into two types:one is chemical reactions-based sensors,and the other is non-covalent interactions-governed sensors.As we know,most chemical reactions are ireversible,thus optical chemosensors based on covalent chemical reactions are often irreversible and single-use,which significantly limits their application in recycling and dynamic monitoring in biological systems.On the contrary,the dynamic reversibility and stimuli-responsive characteristics of supramolecular non-covalent interactions have great advantages in the construction of reversible optical chemosensors,which can make up for the shortcomings of chemical reaction-based sensors.Supramolecular non-covalent interactions mainly include hydrogen bonds,host-guest interactions,electrostatic interactions,van der Waals forces,charge transfer interactions,etc.Among them,host-guest interactions that may integrate a series of non-covalent interactions are of great value in the design and construction of reversible optical chemosensors.In this thesis,the construction and application of reversible supramolecular optical chemosensors are studied from the following aspects:1)Based on the strategy of reversible molecular conformational switching,a supramolecular sensor that can be used for reversible temperature sensing was designed and synthesized;2)Based on the strategy of macrocycle-catalyzed reversible photodimerization,a supramolecular sensor is designed and synthesized that can be used for reversible sensing of UVA and blue light irradiation;3)Based on the strategy of reversible and competitive host-guest self-assembly,a supramolecule fluorescent sensor for reversible detection of phenylalanine(Phe)was designed and synthesized.In chapter 1,the concept and design principles of optical chemosensors,as well as the significance of reversibility for sensors are first elaborated.Secondly,the main types and characteristics of non-covalent interactions involved in the design and construction of supramolecular chemosensors are introduced.Finally,macrocyclic hosts in the host-guest system and their applications in supramolecular chemosensors are introduced in detail.In chapter 2,a strategy based on?-cyclodextrin(?-CD)-induced reversible conformational transformation is proposed and employed to construct a supramolecular system with localized excited(LE)state and intramolecular charge transfer(ICT)state dual emission.By taking advantage of the temperature-modulated equilibrium shift of the assembly-disassembly processes,a reversible supramolecular fluorescent thermometer was constructed.First,a fluorophore N with two functional groups linked by a flexible alkyl chain is synthesized,which can undergo host-guest interactions with?-CD in aqueous solution and embedd into the cavity of?-CD in a unique self-folding conformation,forming a self-assembled complex NCD with LE emission and CT dual emission.The change of temperature induces a shift in the complexation equilibrium,meanwhile the conformation of the guest molecule N is reversibly switched between the two modes of stretching and folding,accompanied by the dynamic and reversible intensity changes of two emissions peaks.Based on this feature,the supramolecular system is used for temperature sensing in solution as well as in live cells with high sensitivity and excellent reversibility.In chapter 3,a strategy based on cucurbit[8]uril(CB[8])catalyzed reversible photodimerization is proposed and employed to construct a supramolecular photochromic system,which can be used to monitor UVA and blue light radiation dosage.First,a photosensitive pyrrolevinylpyridinium derivative M was designed and synthesized,and then a ternary supramolecular complex CB[8](?)M₂ was formed through host-guest interactions with CB[8]in aqueous solution.In the self-assembly system,the catalysis of CB[8]greatly improves the reversible photodimerization kinetics of M.The CB[8]-catalyzed photodimerization/cleavage reactions of M result a reversible color-changing under external light radiation.In terms of application,inspired by the characteristics of CB[8]-regulated photochromism kinetics,CB[8](?)M₂ is used in a time-resolved encryption system.What's more,as a proof of concept,the CB[8](?)M₂ doped hydrogel was further used to monitor the irradiation dosage of long-wave ultraviolet(UVA:320-400 nm)and high-energy blue light(400-460 nm).In chapter 4,CB[8]-based ternary reversible and competitive self-assembly strategy is proposed and employed to construct a supermolecular fluorescent sensor for Phe detection.First,a series of water-soluble fluorescent molecules G1,G2,G3and G4 are designed and synthesized.which are used to construct supramolecular complexes with CB[8].These complexes(CB[8](?)Gn)could response to Phe with fluorescence"turn-on"through competitive host-guest interactions with CB[8]in aqueous solution.Among them,CB[8](?)(G4)₂ exhibits the best selectivity toward Phe with high selectivity and signal-to-noise ratio.The study shows that a new 1:1:1ternary supramolecular complex CB[8](?)G4-Phe may be formed during the re-assembly between CB[8](?)(G4)₂ and Phe.The dynamic and reversible nature of the non-covalent interactions in such competitive host-guest self-assembly system endows the supramolecular sensor with potential of reversible detection of Phe.