Design And Application Of Spiropyran Fluorescent Molecular Switches With Negative Photochromic Properties

In recent years,photochromic molecules have attracted people's attention because of their wide applications in optical recording,sensor devices,smart display windows,and light trigger units in supramolecular systems.Traditional photochromic molecules are mostly triggered by UV light,however,colored isomers can also absorb excitation UV light,the conversion efficiency is relatively low,and short-wavelength UV light will also cause chemical photodegradation of the material itself.In addition,UV light can also cause damage to living cells,which to a certain extent further limits its application in the biological field.Compared with traditional UV light-activated switches,negative photochromic materials can be stimulated by visible light to achieve a colorless state transition.Since colorless isomers do not absorb visible excitation light,it is expected to achieve efficient conversion efficiency.However,most of the reported negative photochromic systems still need to depend on external environmental conditions,especially most of them need to be in solution to complete the conversion process.The solid devices that truly realize the negative photochromic function are still very rare.More importantly,most of these negative photochromic systems have no fluorescence conversion properties.Therefore,optimizing and improving the negative photochromic system is of great significance.It can not only provide new ideas and methods for negative photochromic materials,but also further expand its applications in bioimaging,anti-counterfeiting encryption,chemical sensing and other fields.In the second chapter,In order to reduce the dependence of negative photochromic molecules on the solution environment matrix and further promote its application in solid-state display and other fields,we designed and prepared a pyrene modified nitrospiropyran Py-Sp-NO₂,which does not require substrate assistance,can directly reverse the thermodynamic stability of nitrospiropyran by heating,thereby constructing a new type of negative photochromic solid fluorescent switch molecule.Using the spiropyran skeleton as a model molecule,different spiropyran derivatives substituted with different electron-donating groups and electron-withdrawing groups were synthesized as control molecules,and their thermally induced ring-opening properties and corresponding fluorescent properties were investigated.The DFT theoretical calculation revealed the effect of the substituent effect on the construction of negative photochromic fluorescent molecules.In addition,the effect of intermolecular forces of Py-Sp-NO₂ in different aggregation states such as monodisperse,amorphous powder and crystalline powder on the construction of negative photochromic fluorescent molecules was also studied.The results show that pyrene's flatness,as well as appropriate intermolecular interactions,determine its thermally induced ring-opening performance,which plays an important role in the construction of negative photochromic molecules.At the same time,the introduction of pyrene ensures the good fluorescence performance of the material.The negative photochromic fluorescent molecules thermally stable far-red light and have a very high quantum yield.These characteristics make it have potential application prospects in the field of biological imaging and display.In the third chapter,In order to solve the problem that the negative photochromic material has no fluorescence or only one kind of fluorescence conversion,and try to apply it to the field of biological imaging,we designed and synthesized a new type of negative photochromic nanoparticle based on TPE-Sp-SO₃.By adjusting the dye molecule and the type and ratio of the coating matrix to adjust the luminescence properties and morphology of the nanoparticles,nanoparticle with both fluorescence conversion properties and good particle size distribution were obtained.This nanoparticle can not only achieve the effect of red-green fluorescent reversible switching under visible light and dark conditions,but more importantly,it has little dependence on the environment itself,and has good light stability and light conversion efficiency.After the optical switch test for more than 10 cycles,the sample produced only a slight"light fatigue"effect.Through biological functionalization of nanoparticles,the nanoparticle still have red-green fluorescence conversion properties and have great application prospects in the field of biological imaging.