The impact of lone pair-π interactions on photochromic properties in 1-D naphthalene diimide coordination networks

Lone pair–π interaction is an important but less studied binding force. Generally, it is too weak to influence the physical properties of supramolecular systems. Herein we reported the first example exhibiting the impact of lone pair–π interactions on photochromic properties of naphthalene diimide based coordination networks. In three isostructural 1-D networks, [(DPNDI)ZnX2] (DPNDI = N,N-di(4-pyridyl)-1,4,5,8-naphthalene diimide, X = Cl for 1, X = Br for 2 and X = I for 3), they exhibit different electron-transfer photochromic behaviors due to different lone pair–π interactions between the capped halogen atoms and electron-deficient DPNDI moieties. Specifically, 1 and 2 but not 3 are photochromic, which is attributed to a stronger lone pair–π interaction in 3 than those in 1 and 2. This study anticipates breaking a new path for designing novel photochromic materials through such unnoticeable supramolecular interactions.