Photoinduced multi-color emission of naphthalenediimide radical in different solvents and dynamic anti-counterfeiting film

Developing innovative materials with environmentally stable 1,4,5,8-Naphthalene diimide radicals (NDI−) emissions is significant. In this work, we have successfully constructed an NDI-based material 2-NDI (N, N′-bis(2-butyric acid)-1,4,5,8-naphthalene diimide) that emits strong fluorescence in solvents and polymethyl methacrylate (PMMA) upon irradiation. The radical 2-NDI− exhibits multi-color emission in different solvent systems, and the fluorescence emission is concentration-dependent. It is worth noting that it exhibits a rare dynamic fluorescence in DMF solvent, with the fluorescence color changing from yellow-green to orange and finally to white. Theoretical calculations show that the fluorescence is derived from the Dn-D0 vertical emission of 2-NDI− monomer and excimer. Owing to the outstanding free radical fluorescence emission properties, various films (PMMA systems) based on 2-NDI in different solvents have been successfully made to be applied in multiple dynamic information anti-counterfeiting and encryption. This work achieved simple and stable fluorescence emission based on NDI−, making it a potential candidate for practical applications and providing a new platform for the future design of NDI-based photochromic materials.