Wavelength-Selective Photochromism in a Naphthalenediimide-Based Metal–Organic Framework: Mechanism, Ultrafast Response, and Inkless Printing Applications

This work presents a novel Zn(II)-based metal-organic framework (MOF, named <b>1</b>) incorporating naphthalenediimide (NDI) ligands, which exhibits ultrafast and reversible photochromic properties under irradiation with blue-violet light (395-465 nm). The material exhibits exceptional sensitivity to blue-violet light, enabling rapid color transitions within seconds, a feature rarely reported in NDI-based systems. Structural and spectroscopic analyses reveal that the photochromism originates from photoinduced electron transfer (ET) facilitated by hydrogen bonding and lone pair-π interactions, leading to the formation of NDI radical anions. The MOF also displays unique photomodulated fluorescence, with effective quenching (∼80% reduction) observed under visible light, enabling dual-mode optical switching. Leveraging its wavelength-dependent responsiveness, the material is successfully applied in advanced anticounterfeiting technologies, including inkless printing and fingerprint encryption, showcasing high-contrast patterns and spatially controllable fluorescence. These findings highlight the MOF's potential as a multifunctional photoresponsive material for optoelectronic and security applications.