Regulation Effect of Positional Isomeric Naphthalenedicarboxylic Acids on the Electronic and Photochromic Behaviors of Tripyridyl-Triazine-Based Coordination Polymers

The development of a new strategy for manipulating intermolecular charge transfer (ICT), photoinduced intermolecular electron transfer (PIET), and photochromic properties in coordination polymers (CPs) has attracted considerable interest, yet it remains an enduring challenge. Herein, two tripyridyl-triazine (TPT)-based CPs, [Zn(2-TPT)(1,4-NDC)]·2DMF (1) and [Zn(2-TPT)(2,6-NDC)]·1.5DMF·1.5H2O (2), (2-TPT = 2,4,6-tri-(2-pyridyl)-1,3,5-triazine, 1,4/2,6-NDC = 1,4/2,6-naphthalenedicarboxylic acid), were synthesized via the reaction of the polydentate 2-TPT ligand, Zn2+ ions, and positional isomeric naphthalenedicarboxylic acids of 1,4-NDC/2,6-NDC, respectively. Interestingly, two coordination polymers (CPs) display completely distinguishing photochromic behaviors, which are mainly focused on the photoresponsive rate, discoloration saturation time, and coloration contrast. Positional isomerism of the naphthalenedicarboxylic acids induces significant changes in the spatial arrangement and non-covalent interactions at the interfacial contacts of electron donors (EDs) and electron acceptors (EAs). Such variations further affect the intermolecular charge transfer (ICT) and photoinduced intermolecular electron transfer (PIET) processes, ultimately determining the photochromic properties. Furthermore, 2 has been successfully applied in information anti-counterfeiting. Herein, a handy method is developed to regulate the electronic behaviors in photochromic CPs, which offers an effective strategy for constructing optical functional materials with tunable properties.