Synthesis, Structure, Optical, and Electrochemical Properties of Triple- and Quadruple-Decker Co-facial Tetrathiafulvalene Arrays.

Understanding the details of the electronic structure in face-to-face arranged tetrathiafulvalenes (TTFs) is very important for the design of supramolecular functional materials and superior conductive organic materials. This article is a comprehensive study of the interactions among columnar stacked TTFs using trimeric (trimer) and tetrameric (tetramer) TTFs linked by alkylenedithio groups (-S(CH2 )n S-, n=1-4) as models of triple- and quadruple-decker TTF arrays. Single-crystal X-ray analyses of neutral trimeric TTFs revealed that the three TTF moieties are oriented in a zigzag arrangement. Cyclic voltammetry measurements (CV) reveal that the trimer and tetramer exhibited diverse reversible redox processes with multi-electron transfers, depending on the length of the -S(CH2 )n S- units and substituents. The electronic spectra of the radical cations, prepared by electrochemical oxidation, showed charge resonance (CR) bands in the NIR/IR region (1630-1850 nm), attributed to a mixed valence (MV) state of the triple- and quadruple-decker TTF arrays. In the trimeric systems, the dicationic state (+2; 0.66 cation per TTF unit) was found to be a stable state, whereas the monocationic state (+1) was not observed in the electronic spectra. In the tetrameric system, substituent-dependent redox processes were observed. Moreover, π-trimers and π-tetramers, which show a significant Davydov blueshift in the spectra, are formed in the tricationic (trimer) and tetracationic (tetramer) state. In addition, these attractive interactions are strongly dependent on the length of the linkage unit.