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

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 ∼0.05m ₀ 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.