The Modulation of Photoinduced Intermolecular Electron Transfer in Naphthalenediimide-Based Photochromic Coordination...

The controllability of photoinduced intermolecular electron transfer (PIET) of coordination polymers (CPs) with photochromic performance is of great significance and continues to present a challenge. Here, two naphthalenediimide (NDI)-based photochromic CPs, [Ca(CENDI)(H₂O)(DMF)] (1) and [Ca(CPNDI)(H₂O)₂] (2) (H₂CENDI = N,N'-bis(carboxyethyl)-naphthalenediimide and H₂CPNDI = N,N'-bis(carboxypropyl)-naphthalenediimide), were obtained via the integration of H₂CENDI/H₂CPNDI with Ca²⁺ ions, respectively. Interestingly, structural transformation of a single crystal was realized (i.e., a two-dimensional layer for 1 versus a three-dimensional open framework for 2) by the increase of length of side chain amino acid groups (β-alanine for 1 versus γ-amino butyric acid for 2), which indicates that N-substituents can effectively regulate the single-crystal structures. Meanwhile, 1 and 2 display entirely different photoresponse rate (color transformation time: all are 1 s, Δ_abs: 0.30 for 1 versus 0.13 for 2, coloration saturation time: 7 s for 1 versus 1 min for 2), indicating that the PIET process could also be effectively regulated by varying the N-substituents. Notably, an effective and easy method for regulating the PIET behaviors of CPs has been developed in this paper, paving the way for the construction of controllable functional materials.