Prepration And Fluorescence Properties Of Charge-transfer Cocrystals

1,2,4,5-tetracyanobenzene(TCNB)is a strong electron deficient molecule and also a typical electron acceptor in the feild of crystals.The chromophoric groups of chalcone are separated by keto-vinyl chain,therefore making chalcone exhibits a series of novel optical properties.Charge-transfer cocrystals are cocrystals formed by charge transfer and other interactions,therefore,the physicochemical properties of CT cocrtstals are not merely the addition of donor and acceptor's physical or chemical properties.In this paper,six kinds of cocrystals were prepared,cocrystal I_a,I_b,II and III,the four with chalcone as donor and TCNB as acceptor,cocrystal?and?,the two with solid carboxylic acids as electron donors.After a series of characterization and analysis,the structures,crystal interactions and fluorescence properties of these cocrystals were investigated and studied.The main contents include the following aspects:(1)Three kinds of chalcone,PPPO,PMPPO and PCPPO,were designed and synthesized.The typical electron acceptor,TCNB,was also synthesized by ourselves.Four charge-transfer cocrystals,which are cocrystal I_a,I_b,II and III,were prepared with the three chalcones as electron donor,TCNB as electron acceptor.There are two kinds cocrystal I_a and I_b which are formed from TCNB and PPPO,the donor and acceptor stoichiometric ratio was1:0.5 and 1:1 respectively,and in the other two charge transfer,the stoichiometric ratio of the donor and acceptor is 1:0.5.In the experiment,an interesting phenomenon was also found.The three cocrystals which stoichiometric ratio of 1:0.5 can be obtained from acetic acid solutions.The results of single-crystal X-ray diffraction show that the three chalcone cocrystals are mainly formed by the interaction of?-?interactions and hydrogen bonds and their fluorescence performances are all enhanced.(2)Two cocrystals were obtained from the attempt that aromatic acid were used as electron donors.Cocrystal?is the charge-transfer crystal with vanillic acid as electron donor and TCNB as electron acceptor,and cocrystal?is p-aminobenzoic acid as electron donor and 7,7,8,8-Tetracyanoquinodimethane(TCNQ)as electron acceptor.During the experiment,it was found that both of the charge transfer cocrystals can be obtained from a solution of dichloromethane as a solvent,but vanillic acid-TCNB was also obtained from two single solvents of ethyl acetate and acetonitrile.Through the single-crystal diffraction datas,the stoichiometric ratio of the donor and acceptor is 1:0.5.Although there are?-?interactions and hydrogen bonds in the cocrystal?,the most important role of the structure formation is hydrogen bonds and their fluorescence are quenched.