Elucidating Design Rules toward Enhanced Solid-State Charge Transport in Oligoether-Functionalized Dioxythiophene-Based Alternating Copolymers

This study investigatesthe solid-state charge transport propertiesof the oxidized forms of dioxythiophene-based alternating copolymersconsisting of an oligoether-functionalized 3,4-propylenedioxythiophene(ProDOT) copolymerized with different aryl groups, dimethyl ProDOT(DMP), 3,4-ethylenedioxythiophene (EDOT), and 3,4-phenylenedioxythiophene(PheDOT), respectively, to yield copolymers P(OE3)-D, P(OE3)-E, andP(OE3)-Ph. At a dopant concentration of 5 mM FeTos(3), theelectrical conductivities of these copolymers vary significantly (rangingbetween 9 and 195 S cm(-1)) with the EDOT copolymer,P(OE3)-E, achieving the highest electrical conductivity. UV-vis-NIRand X-ray spectroscopies show differences in both susceptibility tooxidative doping and extent of oxidation for the P(OE3) series, withP(OE3)-E being the most doped. Wide-angle X-ray scattering measurementsindicate that P(OE3)-E generally demonstrates the lowest paracrystallinityvalues in the series, as well as relatively small & pi;-& pi;stacking distances. The significant (i.e., order of magnitude) increasein electrical conductivity of doped P(OE3)-E films versus doped P(OE3)-Dor P(OE3)-Ph films can therefore be attributed to P(OE3)-E exhibitingboth the highest carrier ratios in the P(OE3) series, along with good & pi;-& pi; overlap and local ordering (low paracrystallinityvalues). Furthermore, these trends in the extent of doping and paracrystallinityare consistent with the reduced Fermi energy level and transport functionprefactor parameters calculated using the semilocalized transport(SLoT) model. Observed differences in carrier ratios at the transportedge (c (t)) and reduced Fermi energies [& eta;(c)] suggest a broader electronic band (better overlap andmore delocalization) for the EDOT-incorporating P(OE3)-E polymer relativeto P(OE3)-D and P(OE3)-Ph. Ultimately, we rationalize improvementsin electrical conductivity due to microstructural and doping enhancementscaused by EDOT incorporation, a structure-property relationshipworth considering in the future design of highly electrically conductivesystems.