Quinoid-controlled bond-length alternation enables high-mobility non-fused π-conjugated polymers

Abstract

Achieving high charge-carrier mobility in π-conjugated polymers typically requires the incorporation of fused-ring frameworks that ensure backbone planarity and rigidity (intrachain transport) and π–π stacking (interchain transport). Here we show that high mobility can instead arise from efficient intrachain transport even in fully non-fused polymer backbones through precise control of quinoid resonance and bond-length alternation (BLA). A series of S-Pechmann (SP)-based polymers having alkoxy side chains were designed in which the quinoidal character was systematically tuned by varying the length of the oligothiophene co-units. Increasing quinoidal character markedly suppresses BLA along the polymer backbone, leading to pronounced π-electron delocalization and reduced carrier effective masses as low as ∼0.05m₀ in theory. As a result, the polymers exhibit ambipolar organic field-effect transistor (OFET) characteristics with mobilities of up to 4.4 cm² V⁻¹ s⁻¹ for holes and 3.4 cm² V⁻¹ s⁻¹ for electrons, despite moderate crystallinity and a predominantly face-on orientation that is typically unfavorable for OFET operation. These findings reveal how quinoid-induced modulation of BLA governs intrachain charge transport in conjugated polymers and highlight BLA modulation as a promising molecular design strategy for achieving high mobility in π-conjugated polymers beyond the conventional fused-ring approach.