Size Effect of Arylenediimide π-Conjugate Systems on the Photoresponsive Behaviors in Eu³⁺-Based Coordination Polymers

Various arylenediimides (ADIs) have been applied to construct photoresponsive coordination polymers (CPs), while the size effect of ADI π-conjugate systems on the photoresponsive behaviors in CPs has been overlooked in the past few years. Herein, we emphasize the size effect of ADI π-conjugate systems on photoinduced electron transfer (ET) in CPs, taking two Eu³⁺-based CPs, [Eu(H₂BINDI)(BINDI)0.5(H₂O)₂]·NH₂(CH₃)₂·8H₂O (1) and [Eu₂(BIPMDI)(DMF)₄(NO₃)₂]·H₂O·2DMF (2) [H₄BINDI = N,N'-bis(5-isophthalic acid)naphthalenediimide; H₄BIPMDI = N,N'-bis(5-isophthalic acid)pyromellitic diimide; DMF = N,N-dimethylformamide], as a case. Both 1 and 2 display ET-based photochromic behaviors with distinct photoresponsive rates and coloration contrast, which can contribute to the size effect of diimide cores on the interfacial contacts of electron donors/acceptors. Meanwhile, ET between the neighboring larger NDI cores of the H₄BINDI ligands can block ligand-to-metal charge transfer and quench luminescence of the Eu³⁺ metal center in 1. Therefore, this work will provide a theoretical basis for the development and exploration of photoresponsive materials.