Regioisomeric Polythiophene Derivatives: Synthesis and Structure-Property Relationships for Organic Electronic Devices

Three types of tail-to-tail (PDCBT_TT), head-to-tail (PDCBT_HT), and head-to-head (PDCBT_HH) regioisomeric polythiophene copolymers were synthesized by modification of the substitution positions of their alkoxycarbonyl side-chains. Chain conformation, and optical, electrochemical, morphological, and charge-transport characteristics of the polymers were significantly influenced by their regiochemistry. PDCBT_HH showed an amorphous morphology due to strong steric hindrance between its head-to-head alkoxycarbonyl side-chains, resulting in the poorest performance in organic solar cells and transistors among three types. PDCBT_HT had a regiorandom structure with both head-to-tail and tail-to-head linkages in a polymer chain. As determined by field-effect mobility measurements, a highly regioregular and planar PDCBT_TT exhibited the highest hole mobility (μ = 0.065 cm² V^-1s^-1), which was two orders of magnitude higher than that of the regiorandom PDCBT_HT. The highest photovoltaic performance was also measured for PDCBT_TT:a fullerene acceptor (PC₇₁BM), by maintaining the packed structures of pristine PDCBT^TT polymers in the blend with PC₇₁BM. Altering the topology of alkoxycarbonyl side-chains of the copolymers resulted in significant differences in crystalline morphologies and electrical properties and thus should be carefully considered in the molecular design of organic semiconductors. [Figure not available: see fulltext.].