A Wide-Band-Gap Pyromellitic Diimide-Based Coordination Polymer for Selective and Visual Detection of Ultraviolet Rays

Owing to one of the main factors causing skin cancer by ultraviolet (UV) radiation emitted from the sun, the development of the effective method for selectively detecting UV rays is of great significance for human health. In this work, two compounds, [(H2CMPMD)·2DMF] (1) and [Cd(CMPMD)(DMF)2] (2), were synthesized by successively introducing DMF and Cd2+ ions into the ligand [H2CMPMD] (L) (H2CMPMD = N, N′-bis(carboxymethyl)-pyromellitic diimide). Interestingly, the photochromic performance progressively enhanced from L to 1 and then to 2, which should be mainly attributed to the different interfacial contacts of electron donors/acceptors (EDs/EAs). The continuous regulation of photochromic performance was achieved. Notably, 2 exhibited both high sensitivity and selectivity for the detection of UV rays due to the usage of the PMD ligand with a wide band gap. Furthermore, 2 was developed into a portable test strip (2-paper) for the visual detection of UV rays and information encryption, which enabled its application in practical scenarios. This work not only offers an effective strategy for the continuous modulation of photochromic properties but also presents a simple method for the visual and selective detection of UV rays.