Electrochemical Functions of Nanostructured Liquid Crystals with Electronic and Ionic Conductivity

Nanosegregated liquid crystals are effective to construct nanostructures in which an electronic function couples with an ionic transport. Polarization of ionic species can form local electric fields interacting with electronic charges. In electrochromism, an electrical double layer promotes charge injection from an anode or cathode to an active layer in which the injected charges are transported efficiently, due to the nanostructures of the liquid crystal phase. In chemical doping, dopant ions are accumulated in ion-conductive subdomains and separated from the electron transport channels. This type of the doping is interstitial doping which is different from substitutional doping observed in organic molecular crystals. Side-chain engineering is effective for construction of the nanosegregated liquid crystal phases. Imidazolium units connected to the terminal of alkyl chains of liquid crystalline oligothiophene derivatives promote formation of the nanosegregated structure in which ion-conductive and hole-transporting layers are integrated alternately. Oligosiloxane moieties have a liquid-like property although they induce nanosegregation in liquid crystal phases. Perylene bisimide derivatives bearing oligosiloxane moieties exhibit high solubilities in organic solvents and columnar phases at room temperature. Perylene bisimide derivative bearing two cyclotetrasiloxane rings and one triethylene oxide chain works as a mixed conductor. Polymerized thin films display electrochromism in organic electrolyte solutions and anisotropic electrical conductivity in the doped states.