Oligothiophene functionalized dimethyldihydropyrenes II: electrochemical and conductive properties

Three different types of oligothiophene functionalized dihydropyrene photoswitches, (A) 2-naphthoyldimethyldihydropyrenes functionalized at the 4,9-positions with oligothiophenes, (B) benzodimethyldihydropyrenes functionalized at the 4-positions with oligothiophenes and the 10(11)-position with oligothienylcarbonyl groups, and (C) benzodimethyldihydropyrenes functionalized at the 4,5-positions with oligothiophenes, were studied with the goal of using the change in pi-conjugation between the open and the closed forms of the dihydropyrene (DHP)-metacyclophane (CPD) switch to control electrical conductivity. UV-vis absorption studies were performed to measure the extent to which the attached thienyl oligomers were conjugated with the switch and the ability of the switch when opened or closed to affect conjugation. Of the three types of switches studied, those of type A showed the greatest effect. Solution cyclic voltammetry (CV) for the closed isomers indicated that the first few oxidation peaks were quasi-reversible, but that later ones were irreversible, leading to polymerization. Solution CV experiments on the open CPD form led to electrochemically induced closing to the DHP form. Conductivity studies were performed on undoped thin films of the A-type compound 4 and showed that opening the switch caused a decrease in electrical conductivity, and closing the switch caused an increase in electrical conductivity through the film. Doped films were studied by dual-electrode voltammetry and spectroelectrochemistry and showed that while doping led to an increase in the conductivity of the film it also led to the closing of the open form, preventing the conductivity of the open doped form from being measured.