Dual Photo-/Electrochromic Pyromellitic Diimide-Based Coordination Polymer.

By the combination of N,N'-bis(carboxymethyl)-pyromellitic diimide (H2CMPMD, 1) and zinc ions, a novel PMD-based coordination polymer (CP), [Zn(CMPMD)(DMF)1.5]·0.5DMF (2) (DMF = N,N'-dimethylformamide), has been prepared and characterized. 1 and 2 exhibit completely different photochromic properties, which are mainly reflected in the photoresponsive rate (5 s for 1 vs 1 s for 2) and coloration contrast (from colorless to light green for 1 vs green for 2). This phenomenon should be attributed to the introduction of zinc ions and the consequent formation of the distinct interfacial contacts of electron donors (EDs) and electron acceptors (EAs) (dn-π = 3.404 and 3.448 Å for 1 vs dn-π = 3.343, 3.359, 3.398, and 3.495 Å for 2), suggesting a subtle modulating effect of metal ions on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photochromic behaviors. Interestingly, the photochromic performance of 2 can be enhanced after the removal of coordinated DMF, which might be ascribed to the decrease of the distance of EDs/EAs caused by lattice shrinkage, which further improves the efficiency of PIET. Meanwhile, 2 displays rapid electrochromic behavior with an obvious reversible color change from colorless to green, which can be used in an electrochromic device. This work develops a new type of EA for the construction of stimuli-responsive functional materials with excellent dual photo-/electrochromic properties.

The effect of conjugation degree of aromatic carboxylic acids on electronic and photo-responsive behaviors of naphthalenediimide-based coordination polymers.

Three novel naphthalenediimide-based (NDI-based) coordination polymers (CPs), namely [Cd(3-PMNDI)(2,2'-BPDC)] (1), [Cd2(3-PMNDI)1.5(4,4'-BPDC)2(H2O)3]·DMF (2) and [Cd(3-PMNDI)(4,4'-SDC)] (3) (2,2'-H2BPDC = 2,2'-biphenyldicarboxylic acid, 4,4'-H2BPDC = 4,4'-biphenyldicarboxylic acid, 4,4'-H2SDC = 4,4'-stilbenedicarboxylic acid, 3-PMNDI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalenediimide, and DMF = N,N'-dimethylformamide), have been designed and synthesized here from electron-deficient PMNDI (electron acceptors, EAs) and electron-rich aromatic carboxylic acids (electron donors, EDs) in the presence of cadmium ions. The introduction of aromatic carboxylic acids with different sizes and conjugation degrees leads to the generation of a two-dimensional (2D) layer in 1, a two-fold interpenetrated three-dimensional (3D) network in 2 and an eight-fold interpenetrated 3D framework in 3. Furthermore, the use of distinct electron-donating aromatic carboxylic acids and the consequent different numbers and strengths of lone pair-π and π-π interactions in the interfacial contacts of EDs/EAs give rise to distinct intermolecular charge transfer (ICT) and initial colors of the three CPs, and consequently cause different photoinduced intermolecular electron transfer (PIET) and distinguishing photo-responsive behaviors (weak photochromic performance for 1, excellent photochromic properties for 2 and non-photochromism for 3). This study indicates that an appropriate ICT is beneficial for PIET, but too weak or too strong ICT is not conducive to PIET, which provides an effective strategy for the construction of functional CPs with distinguishing photo-responsive properties through the subtle balance of ICT and PIET.

The modulation effect of auxiliary ligands on photochromic properties of 3D naphthalene diimide coordination polymers.

Two novel naphthalene diimide (NDI) coordination polymers (CPs), [Cd(NicNDI)(4,4'-SBC)] (1) and [Cd(NicNDI)(2,2'-BPC)] (2) (NicNDI = (3-pyridylacylamino)-1,4,5,8-naphthalene diimide, 4,4'-SBC = 4,4'-stilbene dicarboxylic acid, 2,2'-BPC = 2,2'-biphenyl dicarboxylic acid), were designed and prepared by the combination of electron-deficient NicNDI and electron-rich aromatic carboxylic acid ligands in the presence of cadmium ions. The usage of aromatic carboxylic acid ligands with different conjugation degrees, sizes, shapes and charge densities leads to the generation of distinct interpenetrated three-dimensional (3D) frameworks. Interestingly, photochromism of 1 and weak photoactivity of 2 should be attributed to the introduction of different auxiliary ligands and consequently the formation of distinct interfacial contacts of electron donors (EDs)/electron acceptors (EAs) (dπ-π = 3.427 Å, infinite -ED-EA-ED-EA- for 1vs. dπ-π = 3.634 Å, discrete ED-EA-ED for 2), suggesting a subtle modulating effect of auxiliary ligands on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photoresponsive behaviors.

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.

The modulation effect of carboxylic acid ligands on the electron transfer photochromism of NDI-derived coordination polymers.

Four naphthalene diimide (NDI)-derived coordination polymers (CPs), [Cd(3-DPNDI)(o-BDC)] (1), [Cd(3-DPNDI)2(p-BDC)(NO3)] (2), [Cd(3-DPNDI)(NDC)(H2O)2] (3), [Cd(3-DPNDI)(BPC)(H2O)] (4) (3-DPNDI = N,N'-di-(3-pyridyl)-1,4,5,8-naphthalene diimide, o-BDC = phthalic acid, p-BDC = terephthalic acid, NDC = 2,6-naphthalenedicarboxylic acid, BPC = biphenyl-4,4'-dicarboxylic acid), have been designed and prepared. The usage of carboxylic acid ligands with different sizes, shapes and charge densities leads to the distinct resultant architectures of four CPs and divergent weak interactions (lone pair⋯π, π⋯π and C-H⋯π interactions) of electron donors/acceptors, which further lead to the completely different photoinduced electron transfer (PET) and consequent photochromic properties. More specifically, 1 and 2 display excellent photochromic behaviors with a fast photoresponsive rate and high coloration contrast, which are attributed to the suitable interfacial contacts of electron donors/acceptors. However, 3 and 4 are basically optical inert, which could be attributed to the negative effect of the stronger charge transfer (CT) on PET. The present study illustrates the delicate modulating effect of carboxylic acid ligands on the resultant networks, interfacial relationship and PET together with photoresponsive behaviors.

An electron-deficient naphthalene diimide-based metal-organic framework for detecting electron-rich molecules through photo-/chemo-induced chromism.

A novel naphthalene diimide-based metal-organic framework (MOF) {[Zn(3-DPMNI)0.5(NDC)]·3DMF} (1@DMF), (H2NDC = 2,6-naphthalenedicarboxylic acid, DPMNI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalene diimide, DMF = N,N'-dimethylformamide), has been synthesized, which shows a 3D pillar-layer architecture built of carboxylate layers and naphthalene diimide pillars. The compound exhibits outstanding photochromic performance due to photoinduced electron transfer (ET) between the electron-rich guest molecules and electron-deficient host framework (host-guest ET). Of note, the host framework of 1 cannot show a macroscopic color change owing to the absence of the ET pathway. Nevertheless, it exhibits discriminative photochromic behavior in the presence of electron-rich solvents, which is mainly attributed to different electron-donating abilities of guest solvents and distinct interfacial contacts of electron donors/acceptors. Furthermore, the MOF can also show discriminative ET chemochromic response to different sizes and shapes of organic amines, which can be potentially used for the visual detection of electron-rich organic amines, especially n-butylamine (n-BUA).

Photochromic and luminescent switchable iodoargentate hybrids directed by solvated lanthanide cations.

Four iodoargentate hybrids, [Eu(DMSO)8]2[Ag2I5][Ag5I8] (1), [Eu(DMSO)8][Ag7I10] (2), [Tb(DMSO)8]2[Ag2I5][Ag5I8] (3) and [Tb(DMSO)8][Ag6I9] (4) (DMSO = dimethyl sulfoxide), have been rationally synthesized, which display simultaneous photochromic and luminescent switchable performances. Photochromism is due to the photolysis of iodoargentate anions and the consequent generation of Ag0 particles with surface plasmon resonance (SPR) absorption. Meanwhile, luminescent switchable performance is ascribed to intermolecular fluorescence resonance energy transfer (FRET) from fluorescent solvated lanthanide cations to photochromic iodoargentate anions.

Effect of positional isomers on the photochromic behaviors of bipyridyltriazolium chloroantimonate hybrids.

Two chloroantimonate hybrids with isomeric bipyridyltriazoliums and similar packing patterns, {[2-bpt]2[(SbCl5)Cl2]}n (1) and {[4-bpt]2[(SbCl5)Cl2]}n (2) (2-bpt2+ = protonated 3,5-bis(pyridine-2-yl)-1,2,4-triazole, 4-bpt2+ = protonated 3,5-bis(pyridine-4-yl)-1,2,4-triazole), have been designed and synthesized. Distinct intermolecular electronic interactions and photochromic behaviors are attributed to the remarkable modulation of positional isomeric effect on the electron deficiency of the acceptors and donor-acceptor matching relationship. 1 is the first reported photochromic chloroantimonate hybrid.

Non-transient thermo-/photochromism of iodobismuthate hybrids directed by solvated metal cations.

Two iodobismuthate-based organic-inorganic hybrids, [M(DMSO)8][Bi2I9] (M = La (1), Bi (2)), have been successfully designed and synthesized by using solvated metal cations as structure-directing agents (SDAs). 1 displays transient high-temperature thermochromism, which is similar to that of the characteristic low-temperature thermochromic properties of bulk bismuth iodide and iodobismuthate hybrids. In contrast, 2 exhibits distinguishing non-transient thermochromic properties stimulated by the different temperature ranges of the thermal treatments. More importantly, a comparison of the optical inertness of 1 and 2 also reveals novel photochromic behavior. The completely different thermo-/photo-responsive properties of 1 and 2 are mainly ascribed to the different binding abilities of the central metal cations with DMSO molecules, which cause a distinct transformation of the inorganic moiety and consequent modulation of band gaps.

A novel photochromic hybrid containing trinuclear [Cd3Cl12]6- clusters and protonated tripyridyl-triazines.

Incorporation of electron-deficient N-protonated 2,4,6-tri(4-pyridyl)-1,3,5-triazine (H3TPT) into electron-rich chlorocadmate leads to a novel organic-inorganic hybrid [H3TPT]2[Cd3Cl12] (1), which features as a trinuclear anionic cluster [Cd3Cl12]6- with one CdCl6 octahedron and two CdCl4 tetrahedra via edge-sharing mode and exhibits excellent photochromic performance with fast photoresponsive rate, obvious coloration contrast and high thermal stability.

Lattice Water Controlled Photo- and Thermochromism of N-Protonated Carbomethoxypyridinium Iodoargentate Hybrids.

Two iodoargentate hybrids, {[HNOM][AgI2]·H2O} (1) and {[HINOM][AgI2]·H2O} (2) (HNOM+ = N-protonated 3-carbomethoxypyridinium; HINOM+ = N-protonated 4-carbomethoxypyridinium), have been designed and prepared, which were constructed from typical [AgI2]- inorganic chains and cationic hydrogen-bonding supramolecular networks (one-dimensional for 1 and three-dimensional for 2) of lattice water and positional isomeric N-protonated carbomethoxypyridinium. Two hybrids exhibit sensitive photochromism based on intermolecular electron transfer (ET) and thermochromism due to reversible hydration and dehydration and the consequent variation of intermolecular charge transfer (CT). Furthermore, loss of lattice water gives rise to improved photochromic dehydrated form 1T and optically inert dehydrated form 2T, suggesting a delicate modulating effect of lattice contraction on the intermolecular CT and ET as well as consequently photoresponsive behaviors.

Two photochromic iodoargentate hybrids with adjustable photoresponsive mechanism.

Two organic-inorganic iodoargentate hybrids, [(HPBI)·(MeCN)][Ag3I4] (1) and [MPBI][Ag3I4] (2) (HPBI+ = 1-proton-2-phenylbenzimidazolium, MPBI+ = 1,3-dimethyl-2-phenylbenzimidazolium), have been synthesized. They exhibit structure-dependent photochromism with fast response and wide color range (from colorless to purple and dark green in 1 and 2, respectively), which are attributed to a substantially reversible photolysis for 1 and dual photolysis and photoinduced secondary ET for 2.

Halogen-dependent photoinduced electron transfer and chromism of three protonated nicotinohydrazide halozincates.

Three isostructural halozincates, [HNH][ZnX4]·H2O (HNH2+ = protonated nicotinohydrazide, X = I (1), Br (2), Cl (3)), have been synthesized and exhibit halogen-dependent photoinduced electron transfer and chromic properties. Due to the different electron-donating nature of halogen atoms, only iodozincate hybrid 1 can easily undergo photoinduced electron transfer and eye-detectable photochromic behavior, revealing a unique matching rule between a moderate electron acceptor and halozincates.

Bipyridyltriazolium Chlorobismuthate with Thermo-/Photochromic and Photoluminescent Switching Behaviors Based on ET and CT†.

Matched with 3,5-bis(pyridine-2-yl)-1,2,4-triazole (2-bpt), a new electron donor-acceptor-based chlorobismuthate(III) hybrid, [2-bpt]2[Bi2Cl10(H2O)]·5H2O was prepared solvothermally and characterized. The title compound (hydrated form) and its dehydrated form exhibit photo- and thermo-induced intermolecular electron transfer (ET), which correspond to dual ET photo/thermochromism for hydrated form, charge transfer thermochromism during dehydration, and simultaneously photoluminescent responses, respectively.

Stoichiometry-controlled structural and functional variation in two photochromic iodoargentates with a fast and wide range response.

By using 1-methyl-4-(carbomethoxy)pyridinium (MCMP+) as counterions, two iodoargentate hybrids, 1D [MCMP][AgI2] (1) and 3D [MCMP][Ag3I4] (2) have been synthesized and they exhibit rare electron transfer photochromism with a fast response rate, a wide response range and a long-lived charge-separated state in iodometallate systems. Noteworthily, the marked differences in the structure and photochromic performance of 1 and 2 are largely ascribed to the different aggregating behavior of electron-deficient MCMP+ counterions (C-HO hydrogen bonded trimer in 1 and π-π/C-Hπ chain in 2).

Ultrasensitive Photochromic Iodocuprate(I) Hybrid.

By employing in situ methylnicotinohydrazide dication (MNH(2+)) as an electron acceptor, we have constructed an iodocuprate(I) hybrid {[MNH][Cu2I3]2}n (1), which exhibits charge transfer (CT) thermochromism due to the intense absorption of CT and electron transfer (ET) photochromism with high photocoloration contrast and fast response to UV irradiation due to the synergetic effect of valence change of copper ions.

Hydrogen bonds and steric effects induced structural modulation of three layered iodoplumbate hybrids from nonperovskite to perovskite structure.

Directed by diprotonated organic diamines containing both primary and tertiary ammonium groups, three layered iodoplumbate hybrids, {[H2DMPDA][PbI4]}n (1), {[H2DEPDA]4[Pb5I18]}n (2) and {[H2TMEDA][Pb3I8]}n (3) (DMPDA = N,N-dimethyl-1,3-propanediamine, DEPDA = N,N-diethyl-1,3-propanediamine, TMEDA = N,N,N',N'-tetramethylethylenediamine), have been synthesized solvothermally. 1 presents a layered perovskite structure based on corner-sharing PbI6 octahedra, compound 2 consists of a Pb4I20 perovskite motif and a Pb2I10 dimeric motif and compound 3 comprises Pb3I13 units connected by face-sharing and edge-sharing modes. Structural modulations from nonperovskite to perovskite structure are strongly correlated to steric effects and hydrogen bonding interaction at the organic-inorganic interface. Band gaps for 1-3 , estimated as 2.21, 2.58 and 2.73 eV, respectively, also reveal an interesting correlation with structural modulation, and the red shift for 1 is attributed to large Pb-I(equatorial)-Pb bond angles.

Interaction between anionic dyes and cationic flocculant P(AM-DMC) in synthetic solutions.

Copolymer of acrylamide and 2-[(methacryloyloxy)ethyl]trimethylammonium chloride [P(AM-DMC)] is found to be effective to combine anionic dyes with strong aqueous solubility. This work aims mainly at revealing the interaction between anionic dyes and [P(AM-DMC)] by running jar test, spectra analysis and equilibrium dialysis experiments. The results show that P(AM-DMC) effectively decolorizes the tested strong water soluble anionic dyes, such as acidic, reactive and direct dyes, from their aqueous solutions under mild acidic and neutral conditions. Higher cationicity and optimal dose of flocculant P(AM-DMC) have to be used to achieve satisfactory and effective decolorization. Comparison of IR spectra of dye, flocculant P(AM-DMC) and the floc formed indicates chemical interaction occurred between sulfonic groups of dye and quaternary ammonium of flocculant. Plots of r-logC suggest cooperative interaction exists evidently for some dyes tested. Addition of KCl or urea reduces binding extent evidently, which shows the importance of electrostatic and hydrophobic interaction. Therefore the interaction between dyes tested and P(AM-DMC) might be controlled by hydrophobic, cooperative interaction and energetic interaction which includes chemical and electrostatic interactions.