Modular Core-Substituted Naphthalenediimide-Based Metal-Organic Frameworks for Red-Light-Driven Photocatalysis

Red-light-driven photocatalytic reactions present a superior alternative for overcoming inherent limitations of conventional ultraviolet (UV) and blue-light photocatalysis, including shallow penetration depth, photodamage of light-sensitive compounds, and limited reaction selectivity. Nevertheless, molecular engineering strategies for achieving efficient red-light heterogeneous photocatalysts remain scarce and pose significant challenges. Herein, this work designed and synthesized two novel isostructural metal-organic frameworks (MOFs, denoted as NHEt-cNDI-Cu₃ and SEt-cNDI-Cu₃) based on core-substituted naphthalenediimide (cNDI) derived dyes. The two MOFs exhibited comparative high surface area and decent water/chemical stability. Intriguingly, their broad and intense light absorption, which is intrinsically inherited from their constituent cNDI ligands, bestowed them with great promise in long-wavelength light photocatalysis. Especially, NHEt-cNDI-Cu₃ was found to be quite prominent in photocatalyzed sulfide oxidations and oxidative coupling of benzylamine under red-light irradiation. In contrast, the performance of its analogue, SEt-cNDI-Cu_3, was five times lower, although their photocatalytic activity was very close under blue-light excitation. The mechanistic study further elucidated that the LUMO of cNDI-based MOFs governed the photocatalytic reactivity, which furnished a new platform for molecular engineering design of long-wavelength photocatalysts and subsequently boosted sustainable chemistry.