Electron-transfer Photochromic Compound:Design,Synthesis And Opto-optical Switching Properties

Photochromism is a phenomenon that chemical specie can transform reversibly between two states with different absorption spectra,and at least one direction of transition is caused by light.Photochromic compounds have important applications in smart windows,glare protection,data storage,photocatalysis,solar energy conversion and so on due to their useful physicochemical properties that can be switched between two states.In recent years,it has become a hot topic that photochromic compounds are set as molecular switches for switching the optic,electricity,magnetism,adsorption,biological activity and other properties.This paper focuses on studying the design and synthesis of electron-transfer photochromic compounds,and related properties of fluorescence switching,second NLO switching and other aspects,and achieves some innovative results.The main discoveries and innovations:1,Photoactive guest molecules were introduced into a MOF to obtain a new compound,{(H2Bpy)[Cd3(BTC)2]·2H2O}n(1).It found that the lifetime value of its photo-generated charge-separated state is up to two months,and longer than the reported values for known ET photochromic MOF compounds.Moreover,compound 1 also exhibits photoswitchable photoluminescence with a contrast of about 10 times between two states and is higher than those of most known pyridine derivative-based photochromic compounds(usually less than 7 times).These results have been published in the journal of RSC Advances(IF = 3.8)in the SCI.2,We discovered the first compound which has both photoswitchable and thermal swithching second order NLO properties,[(MQ)ZnCl3](3),and the NLO intensity contrast before and after irradiation and heat of its crystal samples are 4.5 and 2 times,respectively.Previously,photochromic materials with the tunable second NLO have been reported by many journals such as AM,JACS,Angew for many times,but they are mostly based on the presence of a film or in solution,and need external optical/electrical field or special media to obtain the presence of second-order NLO properties.Moreover,the known bulk photochromic materials with second-order NLO are not only rather rare,but have much small NLO intensity contrast due to their larger molecules isomerization reaction.So far,we reported the first and the only one electron-transfer photochromic crystalline compounds which have a second-order NLO switchable property in the journal Angew,and discoloration around the NLO intensity contrast is 3 times which less than Compound 3.These results are written for an article.The main contents of this paper:In the first chapter,it introduces the related background of this work,topic basis,and purpose and the main progress;in the second chapter,we mainly show the experimental apparatus and test conditions,the synthesis of photochromic compounds;in the third chapter,it is about the studies on the crystal structures,photochromism,thermochromism and photoswitching properties of the compounds in this paper.