An Intrinsically Conductive Cross-Conjugated Polymer with a Quinhydrone-Like Donor-Acceptor Charge-Transfer Network

Intrinsically conductive polymers free of unstable mobile dopants are highly sought after for stable and reliable electronic performance, yet remain scarce due to synthetic challenges. Here we report poly(3,4-dihydroxythiophene-alt-thiophene-3,4-dione) (HOT-DOT), a novel cross-conjugated polymer and the first polymeric analogue of a quinhydrone-like charge-transfer complex with intrinsic conductivity. HOT-DOT is synthesized through a straightforward three-step route, in which the final air oxidation step spontaneously generates a perfectly balanced 1:1 donor-acceptor architecture that promotes self-doping and stabilizes polarons. The polymer exhibits a narrow bandgap (1.38 eV), broad near-infrared absorption, and high conductivity (∼0.29 S cm^-1), enabled by an ultrasmall π-π stacking distance (3.25 Å) despite its cross-conjugated backbone. Spectroscopic and computational analyses reveal that strong interchain donor-acceptor interactions, reinforced by ammonia coordination, stabilize the self-doped state. HOT-DOT further displays rare positive temperature coefficient (PTC) behavior and long-term ambient stability. As a proof of concept, flexible temperature sensors fabricated from HOT-DOT films show reproducible and linear thermal responses over multiple cycles. This study establishes polymeric charge-transfer complexes as a new design paradigm for intrinsically conductive, dopant-free polymers with distinctive transport and sensing properties.