Structure-property relations of regiosymmetrical 3,4-dioxy-functionalized polythiophenes

We present the synthesis and characterization of novel homo- and copolymers containing mono- and dialkylated 3,4-propylenedioxythiophenes with the purpose of creating new pi-conjugated polymers to be exploited in the field of polymer electronics and photonics. We show that the large seven-membered dioxepine ring attached to the thiophene moiety causes unfavorable steric interactions, especially in the homopolymers; it thus prevents the polymers from adapting a coplanar structure with a short pi-stacking distance in the solid state. We furthermore show that incorporation of less space filling units in the form of unsubstituted thiophene units into the polymer chain reduces these unfavorable interactions and therefore allows for a more coplanar polymer backbone orientation and a shorter pi-stacking distance in the solid state. These findings are based on absorption spectroscopy, electrochemical measurements, X-ray powder diffraction, and conductivity measurements.