TTF-fluorene dyads and their M(CN)2− (M = Ag, Au) salts designed for photoresponsive conducting materialsElectronic supplementary information (ESI) available: NMR charts of dyads 1a-d, 2a-b, and UV-Vis simulated spectra of 1a and 2a calculated on the basis of the TD-DFT method. CCDC 953471-953473. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nj00979c

To explore photoresponsive conducting materials, we developed new tetrathiafulvalene (TTF)-fluorene D-A dyads with a σ-bonded thiomethylene spacer ( 1a-d ) or a π-conjugated ethylene spacer ( 2a-b ) and reported their synthesis, electrochemical and optical properties. Fluorescence studies suggested that the fluorescence from an excited fluorene part is quenched by an intramolecular electron transfer process from the electron-donating TTF part to the fluorene part, and the intramolecular interaction through the π-conjugated ethylene spacer is stronger and shows more suppression than the non-planar σ-bonded thiomethylene spacer. We also investigated photoelectric conversion functionality by a photoelectrochemical method using the thin films of dyads 1-2 spin-coated on ITO-coated glass substrates. We observed electric current generation that depends on the absorption spectra of thin films, suggesting that absorbed photons are converted to electric currents on the thin film/ITO electrode. Crystal structure analysis and measurement of photoconductivity of a single crystalline sample of molecule 1d having 4,5-bis(methylthio)-substituents suggest generation of photocurrents along the stacking direction of the TTF parts by the photoinduced intramolecular electron transfer and the resultant charge-separated state. Furthermore, we also reported the crystal structure analyses, photoconductivity and magnetic properties of the cation radical salts, 2b 2 M(CN) 2 (M = Ag, Au), where 2b contains a 4,5-ethylenedithio-substituent. The Ag(CN) 2 salt showed a semiconducting behaviour with a room temperature conductivity of 0.088 S cm −1 due to a half-filled Mott insulating band structure of this crystal that originates from a strongly dimerized intermolecular interaction. Upon photoirradiation, this salt showed a slight enhancement of conductivities of ca. 14%. New D-A type TTF-fluorene dyads with a σ-bonded thiomethylene spacer 1 and a π-conjugated ethylene spacer 2 are investigated.