A panchromatic hybrid crystal of anionic iodoplumbate nanowires and J-aggregated protonated naphthalene diimides has been formed through charge-assisted anion-π and lone pair-π interactions, which exhibits unusually long-lived charge-separated states even upon the irradiation of indoor lighting.

A stable three-dimensional coordination polymer, [Eu3(bcbp)3(NO3)7(OH)2] n (1) (H 2 bcbp·2Cl = 1,1′-bis­(4-carboxyphenyl)-(4,4′-bipyridinium) dichloride), was prepared by the solvothermal reaction of Eu­(NO3)3·6H2O and H 2 bcbp·2Cl in methanol, which was characterized by infrared spectroscopy, single-crystal X-ray diffraction, powder X-ray diffraction, and thermogravimetric analyses. In the solid state, 1 consists of an unusual trinuclear Eu­(III) unit (Eu3(CO2)6(NO3)7(OH), Eu3–SBU), which further connects to six neighboring ones through six bcbp ligands to form a three-dimensional network. As expected, 1 exhibits a strong red-light emission at ambient temperature. Due to the presence of the electron-deficient bipyridinium moiety in the conjugation, this emission is selectively quenched by electron-rich organic amine compounds with high sensitivity and exhibits a prominent visual color change.

Four metal–organic coordination compounds Zn2(bcbp)­Cl4 (1), Zn­(bcbp)­(PO3F) (2), [CdCl­(Hbcbp)­(bcbp)]­·(ClO4)2 (3), and [Cd2(bcbp)4]­·(ClO4)·F3 (4) (H2bcbp·2PF6 = 1,1′-bis­(4-carboxyphenyl)-(4,4′-bipyridinium) hexafluorophosphate) have been synthesized via a solvothermal method and structurally characterized. Compound 1 is a 1D coordination polymer, while compound 2 shows a 2D + 2D → 3D inclined polycatenation structure. In the case of compound 3, due to the capped chlorine atoms and uncoordinated carboxyl of bcbp ligand, it exhibits a 1D T-shaped coordination configuration. Compound 4 is an unprecedented 13-fold interpenetrating structure with huge diamondoid frameworks. Because of the presence of electron-deficient bipyridinium moieties, the photochromic behaviors of these compounds have also been studied. Interestingly, only compounds 1–3 exhibit color changes under light irradiation. The impact of these anions on the photochromic process is discussed.

Interpenetration is an intrinsic behaviour for the porous coordination networks. To prevent the interpenetration, a common strategy is the imposition of geometric or steric restrictions by incorporating bulky moieties into organic tectons. So far, most of the available incorporations have been achieved through a covalent connection, while few involved in the non-covalent weak interactions. In this paper, we have reported that such interpenetration can be prevented by the less common lone pair-π interactions. By imposing the lone pair-π interactions through the addition of lone-pair-bearing N-methylpyrrolidin-2-one or iodine, combinations of rigid naphthalene diimide tectons bearing two divergently oriented pyridyl units at both imide extremities with ZnSiF6 led to non-interpenetrated cuboid 3-D coordination networks that should have been interpenetrated. In addition, such close-contacting lone pair-π interactions between electron donors and acceptors have also been demonstrated to play a key role in their photochromic properties.

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.