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

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)] (<b>1</b>) and [Ca(CPNDI)(H₂O)₂] (<b>2</b>) (H₂CENDI = <i>N</i>,<i>N</i>'-bis(carboxyethyl)-naphthalenediimide and H₂CPNDI = <i>N</i>,<i>N</i>'-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 <b>1</b> versus a three-dimensional open framework for <b>2</b>) by the increase of length of side chain amino acid groups (β-alanine for <b>1</b> versus γ-amino butyric acid for <b>2</b>), which indicates that <i>N</i>-substituents can effectively regulate the single-crystal structures. Meanwhile, <b>1</b> and <b>2</b> display entirely different photoresponse rate (color transformation time: all are 1 s, Δ_abs: 0.30 for <b>1</b> versus 0.13 for <b>2</b>, coloration saturation time: 7 s for <b>1</b> versus 1 min for <b>2</b>), indicating that the PIET process could also be effectively regulated by varying the <i>N</i>-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.