A New D-A Derivative with a 1,3-Dithiol-2-ylidene Unit: Structural, Spectroscopic and Theoretical Studies

A novel D-A compound, [Cu(L)2Cl2]·2CH2Cl2 ML, has been synthesized based on 4′,5′-diaza-9′-(4,5-bis(benzylthio)-1,3-dithiole-2-ylidene)-fluorene ((C11N2H6)(C3S2)(SCH2C6H5)2, L). Both ML and L are further characterized by elemental analysis, IR, 1H and 13C NMR. Single-crystal X-ray diffraction shows ML displays a 3-D supramolecular network built by the neutral mononuclear unit [Cu(L)2Cl2] via hydrogen bonds, π–π stacking and S⋯S interactions. The UV–Vis spectra show the lowest-energy absorption band (431nm) of ML is red-shifted compared to that of L (415nm). The electrochemistry behavior shows that while the HOMO level of the ML is lowered by L coordinating with the Cu2+ ion, the oxidative potentials are increased (1.19 to 1.37V). Photocurrent measurements show the intramolecular charge transfer (ICT) of L should be easier than that of ML. The results of the reorganization energy obtained from DFT calculations (λi: 0.25eV for L, 0.82eV for ML) reveal the lower reorganization energy is of great benefit to carrier transport within L. These results are in good agreement with those experimentally obtained by CV, UV–Vis, fluorescence and photocurrent measurements.