A Mg-CP with <i>in Situ</i> Encapsulated Photochromic Guest as Sensitive Fluorescence Sensor for Fe³⁺/Cr³⁺ Ions and Nitro-Explosives

Abstract

Here we report a fluorescent magnesium coordination polymer (Mg-CP), namely, [CH₃-dpb]₂[Mg₃(1,4-NDC)₄(μ-H₂O)₂(CH₃OH)(H₂O)]·1.5H₂O (1, 1,4-H₂NDC = 1,4-naphthalene dicarboxylic acid, dpb = 1,4-bis(pyrid-4-yl)benzene). Compound 1 possesses a three-dimensional (3D) host-guest structure constructed by the 1,4-NDC linkers bridging the linear trinuclear secondary building units of [Mg₃(COO)₈(μ-H₂O)₂]. The dpb molecules were in situ reacted with CH₃OH resulting in photochromic cations of [CH₃-dpb]⁺ that acted as guests located in the channels parallel to the b-axis. Photoluminescence (PL) studies indicated that 1 showed a strong green emission demonstrating sensitive fluorescence sensing of Fe³⁺/Cr³⁺ metal ions and nitro-explosive compounds. Compound 1 represents the first PL Mg-CP as a fluorescent probe for detecting metal ions. Moreover, because of the in situ encapsulation of photochromic [CH₃-dpb]⁺ guests, 1 exhibited reversible photochromic behavior.