Self-recovering ultraviolet-sensitive photochromic naphthalenediimide-based coordination networks: rapid fluorescence recognition of p-substituted nitrobenzenes

Abstract

Naphthalenediimide (NDI) derivatives have attracted extensive attention due to their photoresponsive properties. Here, we report a series of novel transition metal coordination networks (CNs): Co-CMNDI, Ni-CMNDI, and Cu-CMNDI, which are constructed from N,N′-bis(carboxymethyl)-1,4,5,8-naphthalenediimide (H₂CMNDI) and the corresponding metal salts. The structures were characterized in detail by microanalysis. Structural analysis shows that the frameworks of Co-CMNDI and Cu-CMNDI are 3-periodic fsc nets, while Ni-CMNDI is a 2-periodic sql net. They are sensitive to ultraviolet light, and their color can be changed with a change in the radiation time or intensity. The reversibility of their photochromic behavior and the positive correlation between the color change and ultraviolet intensity makes them possible candidates as UV colorimetric cards in the future. Besides this, the three CNs can be used as fluorescence detectors of three nitroaromatics: p-nitroaniline (PNA), p-nitrophenol (PNP), and p-dinitrobenzene (PDNB), from two emission peaks. At the same time, we introduce a concept of a quenching recognition constant (K_QR), which can be used to better compare the recognition effects of the recognizers. The competitive absorption and photoinduced electron transfer between the analytes and recognizer are the main reasons for the fluorescence quenching. This work provides a novel design idea and materials for future multi-functional sensors.