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]·2CH2Cl2ML, 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 (431 nm) of ML is red-shifted compared to that of L (415 nm). 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 1.37 V). 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: 0.25 eV for L, 0.82 eV 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.

Graphical abstractAn obtained D-A derivative with the 1,3-dithiol-2-ylidene unit indicates a certain electrical conductivity based on measurements of CV, UV–Vis, fluorescence and photocurrents, as well as DFT calculations.Figure optionsDownload full-size imageDownload as PowerPoint slide