Preparation And Photochromic Properties Research Of Pyromellitic Diimide Based Electron Donor-Acceptor Systems

Electron transfer(ET)based photochromic materials show important practical or potential applications in the fields of sensing,protection,display and switching etc.,due to their excellent visual detection performance.The main performance indexes of ET based photochromic materials for the commercialization are reflected in three aspects:the photoresponsive rate and coloration contrast in the process of coloration;the reversibility in the process of decoloration;and the fatigue resistance performance during the process of coloration-decoloration.Until now,some important breakthroughs have been made in the photoresponsive rate and coloration contrast of ET based photochromic materials.However,the commercial applications of these materials have been largely limited by their relatively poor reversibility and cyclic properties.Therefore,to realize the fast reversibility and improve the fatigue resistance performance of the electron donor-acceptor systems,have been the key scientific issues to be addressed for the performance optimization of ET photochromic materials,in which the reasonable control of the donoating-accepting ability and interfacial relationship between the electron donors and acceptors is of primary importance.Pyromellitic diimide derivatives(PMDs)possess a large positive quadrupole moment and strong molecular polarizability,which are a class of electron-deficient acceptors with adjustable band structure.Firstly,by anchoring different functional groups at both ends of the imide ring,their electron-accepting ability can be modulatedwithin certain range,so that it can effectively match with different electron-rich donors in the rule of electron donating-accepting ability.Secondly,the electron-deficient acceptors of PMDs have low?-electron density,which are easy to interact with electron-rich donors form flexible and diverse intermolecular ET channels through different weak interactions,to further realize the matching rule of interfacial relationship in the electron-donor systems.Therefore,in this thesis,four PMDs based organic compounds with different supramolecular stacking have been constructed by anchoring different types of substituent groups in the PMDs electron-deficient centers,to realize the effective modulating of photoresponsive rate and coloration contrast of ET based organic photochromic molecules.On the basis of the above,four PMDs based porous coordination polymers have been contructed via the assembly of4-PMPMD acceptors and different types of carboxylate electron donors.The problems of reversibility and cyclicality of such photochromic materials have been effectively addressed in order to realize the rapid reversibility and ultra-strong fatigue resistance.The main results of this thesis are as follows:1.Four PMDs based electron donor-acceptor organic compounds,2-PMPMD(1),3-PMPMD(2),4-PMPMD(3)and BMPMD(4)(PMPMD=N,N'-Bis(2/3/4-pyridylmethyl)-pyromellitic diimide,BMPMD=N,N'-dibenzylpyromellitic diimide)were successfully constructed by anchoring different types of substituents(positional isomeric aminomethylpyridine and benzylamine)at both ends of the imide ring through amidation reaction.Four compounds exhibit ET photochromic behaviors with different photoresponsive rates and color contrast,which are mainly attributed to the different number and strengths of lone pair-?interactions between adjacent PMDs molecules,showing the modulating effect of different substituents on the electron acceptor ability,the interfacial relationship of electron donors/acceptors,and consequently photochromic properties of PMDs.In particular,4-PMPMD with excellent photochromic properties provides experimental and theoretical support for the subsequent exploration of the reversibility and fatigue resistance of ET based organic-inorganic hybrid photochromic systems.2.Four PMDs based porous coordination polymers[Zn(4-PMPMD)(HBTC)](5),[Cd(4-PMPMD)(HBTC)(H₂O)](6),[Cd(4-PMPMD)(HBTC)](7),[Cd(4-PMPMD)(p-BDC)](8)(H₃BTC=1,3,5-benze-netricarboxylic acid,p-H₂BDC=p-phthalic acid)were constructed by assembly of 4-PMPMD electron acceptor and different types of metal carboxylate electron donors.All compounds 5-8 exhibit photoinduced intermolecular ET and excellent photochromic properties(fast photoresponsive rate,obvious color change,ultra-fast reversibility and ultra-strong fatigue resistance),which are mainly attributed to the rational matching of electron donoating-accepting ability and interfacial relationship of electron donors/acceptors.Compared with the reported ET based photochromic materials,fast photoreversibility and ultra-strong fatigue resistance(the number of coloration-decoloration cycles exceeds 160 times)of 5,fast automatic decoloration of 6 and 7,dual thermo-and photo-chromic performance of 8,provide strong theoretical and experimental support for the practical application of ET photochromic materials.