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Heteroatom substitution is a powerful tool to tune the intra- and intermolecular structure of conjugated polymers as well as their resulting optoelectronic and electrochemical properties. A series of oligoethylene glycol bithiophene chalcogenophene polymers (p(g3T2-X)) with systematically varied furan, thiophene, selenophene, and tellurophene comonomers have been synthesized for mixed ionic-electronic conducting applications. Their microstructures have been thoroughly characterized ex situ and in situ with X-ray scattering, and their mixed conducting properties have been probed in electrochemical transistor testbeds. Chalcogenophene heteroatom choice was found to clearly dictate the polymer microstructure (crystallite dimensionality and orientation) and tune mixed conducting properties. Proceeding down Group 16, from O to Se systematically directed the molecular ordering of 2D polymer crystallites from face-on (O) to mixed (S) to edge-on (Se) orientations, with Te driving the polymer to form well-oriented edge-on 3D crystallites. Heteroatom dictated crystallite quality, and orientation tuned relative ionic transport by 2 orders of magnitude. Hole mobility (μhole) and mixed conducting figure of merit (μC*) were each tuned over an order of magnitude depending on heteroatom choice, with the Te-containing polymer reaching μhole = 3.60 cm2 V–1 s–1 and μC* = 483 F cm–1 V–1 s–1, due to improved molecular ordering. Insights from this polymer series highlight target microstructures for enhanced mixed conduction in future conjugated polymers.
Paulsen et al. (Mon,) studied this question.