Surface-Coordinated Gas-Solid Polymerization Enables Quasi-2D Polyphenylacetylene Single-Crystalline Nanoribbons

Two-dimensional (2D) conjugated polymer single crystals are highly desirable for optoelectronics, yet their realization is limited by the intrinsic coupling between molecular-weight buildup and chain entanglement, which disrupts long-range order. Here, we report a gas-solid interfacial polymerization strategy that decouples monomer diffusion from chain propagation, enabling the growth of quasi-2D polyphenylacetylene (PPA) single-crystalline nanoribbons on Cu/CuO_x surfaces. This process is likely enabled by surface coordination-assisted activation of phenylacetylene and directional π-stacking-driven assembly, which suppress chain entanglement and promote crystallographic ordering. As a result, micrometer-scale PPA single-crystalline nanoribbons with left-handed cis-transoidal helical chains and long-range crystallinity are obtained. Under an ideal fully extended-chain model, the PPA chains exhibit a geometrically estimated upper-bound molecular weight of up to ∼3.7 × 10⁹ g mol^{- 1}. The resulting PPA nanoribbons exhibit efficient charge transport and broadband photodetection from 375 to 1550 nm, with a responsivity of 30.1 A W^{- 1} and a detectivity of 8.65 × 10^{1 2} Jones. This interfacial synthesis strategy provides a route to overcoming the trade-off between molecular-weight buildup and structural order in conjugated polymers, offering opportunities for quasi-2D polymer semiconductors in flexible optoelectronics and programmable chiral materials.