Covalent organic frameworks (COFs) can exhibit high specific surface area and catalytic activity, but traditional solution-based synthesis methods often lead to insoluble and infusible powders or fragile films on solution surface. Herein we report large-area –C=N– linked two-dimensional (2D) COF films with controllable thicknesses via vapor induced conversion in a chemical vapor deposition (CVD) system. The assembly process is achieved by reversible Schiff base polycondensation between PyTTA film and TPA vapor, which results in a uniform organic framework film directly on growth substrate, and is driven by π‐π stacking interactions with the aid of water and acetic acid. Wafer-scale 2D COF films with different structures have been successfully synthesized by adjusting their building blocks, suggesting its generic applicability. The carrier mobility of PyTTA-TPA COF films can reach 1.89 × 10−3 cm2 V−1 s−1. When employed as catalysts in hydrogen evolution reaction (HER), they show high electrocatalytic activity compared with metal-free COFs or even some metallic catalysts. Our results represent a versatile route for the direct construction of large-area uniform 2D COF films on substrates towards multi-functional applications of 2D π‐conjugated systems.
Donor−acceptor (D−A) conjugated polymers with the band gaps below 1.0 eV can exhibit unique near-infrared (NIR) activities and multiple functional applications. However, it is still a big challenge to develop such materials because of the scarcity of effective synthetic strategies and strong acceptor building blocks. Herein, we report the design, synthesis, and application of two novel indanone-condensed thiadiazolo[3,4-g]quinoxaline (TQ) acceptor units, which display high electron affinities and low-lying lowest unoccupied molecular orbital (LUMO) levels because of the incorporation of auxiliary electron-deficient carbonyl or cyano groups into the TQ core. Moreover, two low band gap D−A conjugated polymers are synthesized via Stille condensation reactions between the newly developed TQ acceptor units and 2,5-bis(3-(2-decyltetradecyl)thiophen-2-yl)thieno-[3,2-b]thiophene donor units. The effect of the substitute groups (carbonyl and cyano groups) on the geometry, optical property, electronic structure [highest occupied molecular orbital (HOMO)/ LUMO levels and band gap], film organization, and charge transport of the polymers are discussed carefully. The resulting polymers exhibit very broad NIR absorptions extended to around 1880 nm, deep-lying LUMO energy levels (<−3.90 eV), and low optical band gaps (∼0.66 eV). Investigation of field-effect transistor properties indicates that both polymers show a wellbalanced ambipolar transport behavior, affording the hole/electron mobilities of 1.3 × 10 −3 and 2.0 × 10 −3 cm 2 V −1 s −1 , respectively. These results indicate that both newly developed TQ acceptors are excellent building blocks for the development of novel π-conjugated systems with low band gap and high NIR activity.
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