Vinylene-bridged naphthalenediimide-based dual-acceptor copolymers for thin-film transistors and solar steam generation†

Abstract

Recent studies have shown that introducing vinylene bridges into naphthalenediimide (NDI)-based dual-acceptor copolymers is an effective strategy to improve backbone coplanarity and charge transport properties in organic field-effect transistors (OFETs). However, their potential as multifunctional materials for broader optoelectronic applications remains unexplored. In this study, we designed and synthesized four vinylene-bridged NDI (vNDI)-based conjugated polymers containing benzothiadiazole (S), benzotriazole (N), triazolobenzothiadiazole (NS), and benzobistriazole (NN) as second acceptors. Structural analysis revealed that the backbone conformation and electron-withdrawing ability of the acceptors significantly influence optical and electronic properties. Among them, vNDI-NS exhibited the narrowest optical bandgap (1.05 eV), while vNDI-N displayed the highest ambipolar mobility in OFETs, attributed to enhanced crystallinity and improved π–π stacking. Furthermore, these polymers were applied as photothermal membranes in solar steam generation (SSG) devices. Films based on vNDI-NS and vNDI-NN achieved solar-to-vapor conversion efficiencies of 58.3% and 56.4%, respectively, under 1 sun illumination. This study expands the applications of vNDI-based polymers beyond OFETs, providing a dual-functional platform combining electrical and photothermal performance.