Mixed ionic/electronic conduction in a oligoethyleneglycol-terminated oligothiophene rod-coil oligomer

Developing and studying materials that conduct both electronic and ionic charges on the nanometer length scale is of considerable interest for a wide range of energy harvesting and storage applications. In this work, we report the design, synthesis and characterization of tetraethyleneglycol monomethyl ether-terminated quaterthiophene rod-coil oligomer 4T/PEG4 thin film that shows both ionic and electronic conduction characteristics. At room temperature, 4T/PEG4 only exhibits ionic conductivity on the order of 10^-5S/cm upon blending with LiTFSI at the optimum doping concentration r = 0.1. The electronic conduction can be introduced into the bolaamphiphile by doping F4TCNQ into LiTFSI-doped 4T/PEG4 thin film via vapor doping method. The electronic conductivity as high as 2 x 10^-3 S/cm in 4T/PEG4 can be achieved without sacrificing ionic conductivity. UV-vis absorption spectroscopy measurement indicates that charge transfer complex is the dominant doping mechanism, suggesting the formation of co-crystal between F4TCNQ and the quaterthiophene unit of 4T/PEG4. Our results show that 4T/PEG4 is a promising candidate to study the combination of both ionic and electronic conductivities in a single materials system.