Charge transfer stimulated visible-light photochromism of naphthalenediimide-based zinc halide coordination polymers for detecting/filtering harmful blue rays

Abstract

Due to high penetration, low photo-toxicity, and low background signal of red-shifted visible light, the development of visible-light photochromic materials is of great importance but still a challenging task. In this study, four one-dimensional (1D) naphthalenediimide (NDI) photochromic coordination polymers (CPs), namely {[ZnCl₂(4-PMNDI)]·H₂O}_n (1), {[ZnBr₂(4-PMNDI)]·2H₂O}_n (2), {[ZnCl₂(3-PMNDI)]}_n (3) and {[ZnBr₂(3-PMNDI)]}_n (4) (4-/3-PMNDI = N,N’-bis(4-/3-pyridylmethyl)-1,4,5,8-naphthalenediimide), have been designed and synthesized by the combination of positional isomeric electron-deficient PMNDI (electron acceptors, EAs) and electron-rich zinc halides (electron donors, EDs) under solvothermal conditions. The distinct photochromic properties of 1–4 should be attributed to the formation of different interfacial contacts of EDs/EAs due to the introduction of 4-/3-PMNDI positional isomers and different halogen anions. Noteworthily, the much more rapid photoresponsive rates of visible-light photochromism for 1–4 with respect to those of UV-light photochromism exposits that the electronic absorption band of charge transfer (CT) interactions in the visible light region can effectively trigger electron transfer (ET) promptly. Furthermore, 1 exhibits a high photosensitivity property in response to wavelengths of 390–450 nm, and it can be applied in detection/filtration of harmful blue rays. This work breaks through an orthodox concept that the ET reaction can only be activated by the electronic absorption band of EDs or EAs (usually in the UV light region), and provides a simple and feasible method for the construction of visible-light photochromic materials.