The impact of positional isomerism on electronic and photochromic properties of 1D zinc-based naphthalene diimide coordination polymers

Abstract

Two 1D zinc-based naphthalene diimide coordination polymers, [ZnCl₂(3-DPNDI)]·H₂O (1) and [ZnCl₂(4-DPNDI)]·DMA (2) (3/4-DPNDI = (3/4-pyridyl)-1,4,5,8-naphthalene diimide, DMA = dimethylacetamide), have been designed and prepared through a strategy based on positional isomerism. The usage of positional isomers leads to the linear shaped chain for 1 and zigzag shaped chain for 2, which are further assembled into distinct supramolecular networks through different numbers and strength of lone pair–π interactions. Furthermore, the two compounds exhibit different photochromic properties based on the photoinduced electron transfer (ET) between electron-rich O/Cl atoms and electron-deficient DPNDI centroids. By comparison with 2, the excellent photochromic behavior with a fast photoresponsive rate and high coloration contrast of 1 should be attributed to the maximization of numbers and strength of lone pair–π interactions between donors and acceptors, implying the delicate modulating effect of positional isomerism on the distinct interfacial position and photoinduced electron transfer together with photoresponsive behaviors.