Synthesis And Theoretical Study Of Organic Molecules With D-Ï€-A Conjugated Structure

Tetrathiafulvalene (TTF) is famous as a π-electron donor in the field of organic molecular metals, the study of which was initiated in the early 1970s with the first observations of metallic behavior in the celebrated charge transfer (CT) complex TTF-TCNQ. Not only a component of molecular conductors, TTF and its derivatives are versatile building blocks in many areas of materials chemistry. Nowadays, as an efficient proaromatic donor unit 1,3-dithiol-2-ylidene moiety also has been studied to prepare new NLO-phores, on account of the contribution of the aromatic 1,3-dithiolium to the charge-separated state. As a result, Functionalized modification of 1,3-dithiol-2-ylidene unit has received more and more interest in recent years.The main task of this paper was, therefore, to design and synthesize a series of 1,3-dithiole-2-ylidene derivatives provided with D-π-A structures: [1,3]dithiol-2-ylidene-(4-nitro-phenyl)-imine; 4,5-Bis-(methylthio)-[1,3]dithiol-2-ylidene-(4-nitro-phenyl)-imine; 4,5-Bis-(ethylenedithio)-[1,3]dithiol-2-ylidene-(4-nitro-phenyl)-imine; 4,5-Bis-(benzylthio)-[1,3]dithiol-2-ylidene-(4-nitro-phenyl)-imine; 4,5-Bis-(dodecyl-thio)-[1,3]-dithiol-2-ylidene-(4-nitro-phenyl)-imine; 2-(4,5-Bis-dodecyl-sulfanyl-[1,3]dithiol-2-ylidene)-malononitrile, which were characterized and identified by 1H NMR, MS, (EI), FT-IR and UV-Vis spectra. At the same time, electrochemical behaviors were recorded by means of cyclic voltammetry. It was shown in CV testing that there were mainly two pairs of redox peaks coming from the 1,3-dithiole ring and nitro group respectively, Moreover, the oxidation potential values shift anodically with the increasing of scan rate.Density functional theory was employed to study the geometry structures and electronic structures of the products. In addition, on the basis of the calculating resultswe worked out the electronic spectroscopic properties of the target compounds by TD-DFT approach, the results are in good accordance with the experimental values. On the side of second order NLO coefficient calculations using TDHF method, by the discussion of the relations between structures and properties it can be seen that with the increasing capabilities of electron-donor and electron-acceptor the β values of D-π-A systems will increase correspondingly due to the cooperation effect of D and A.