Synthesis And Photochromic Properties Of Benzothiophene Thiosemicarbazone Derivatives

Organic photochromic compounds exhibit wide the potential application in the fields of optical switching,data storage,nonlinear optical materials,photoelectric devices and so on duing to their special photochemistry and photophysical properties,and it have attracted much attention from researchers at home and abroad.There are relatively less reports on solid-state photochromic compounds compared with the photochromc compounds in solution.Besides,the complicated synthesis process,poor thermal stability and poor fatigue resistance of solid-state photochromic compounds limits their practical application.Thus,the development of new solid-state photochromic compounds has become one of the hot topics.In this paper,a series of benzothiophene thiosemicarbazone derivatives with photochromic properties in solid-state were synthesized by introducing different substituents at different sites of thiosemicarbazone derivatives.The structure and composition of the synthesized compounds was characterized,the photochemical properties of the compounds were tested,the structure-activity relationship of the compounds was investigated and the photochromic mechanism of the compounds was discussed.In order to expand its application,1-(benzo[b]thiophene-2-ylmethylene)-4-ethylthiosemicarbazone(BS2C-ETSC)which shows excellent photochromic properties was hybridized with PVP,and nanofibrous membranes of BS2C-ETSC@PVP were prepared by electrospinning,which showed improved reversible photochromic properties in comparison of compound itself,which laid a solid foundation for the research and application of high performance photochromic films.The details are as follows:1.A series of 1-(5-substituents-benzo[b]thiophene-2-ylmethylene/ethylene)-4-substituents-thiosemicarbazone were synthesized.The effects of substituted groups at the 4-position and 1-position of thiosemicarbazone derivatives on the photochromic properties were discussed and the structure-activity relationship of the compounds was preliminarily revealed.We found that the compounds with longer alkyl chain at 4-position in a certain range require shorter irradiation time to reach the photostationary state,the photochromic rate of these compounds increases with the enhancement of conjugation at 4-position.By modifying the structure of thiosemicarbazone derivatives at 1-position,we found that the compounds possess a poor photochromic property with the increasing of the steric hindrance at 1-position,and the photochromic properties of thiosemicarbazone derivatives disappeared when there is an electron-donating group or electron-withdrawing group on the benzothiophene ring.2.Based on the single crystal structures,the FT-IR spectra and theory calculations,the proposed photochromic mechanism of BS2C-ETSC was the intermolecular proton transfer between the thio-keto and thio-enol tautomer under irradiation of UV/Vis light.3.Nanofibrou membranes that also possess photochromic properties were prepared by electrospinning.By optimizing the composition of electrospun solution,the hybrid membranes have an excellent photochromic properties by choosing the appropriate solvent(DMF),by controlling the PVP content at 10 wt% and the BS2C-ETSC content at 1 wt%,which showed improved photochromic rate and recovery percentage in comparison of the compound itself.