Dipyridine Units Research Articles

Highly robust supramolecular polymer networks crosslinked by a tiny amount of metallacycles

Supramolecular polymeric materials have exhibited attractive features such as self-healing, reversibility, and stimuli-responsiveness. However, on account of the weak bonding nature of most noncovalent interactions, it remains a great challenge to construct supramolecular polymeric materials with high robustness. Moreover, high usage of supramolecular units is usually necessary to promote the formation of robust supramolecular polymeric materials, which restrains their applications. Herein, we describe the construction of highly robust supramolecular polymer networks by using only a tiny amount of metallacycles as the supramolecular crosslinkers. A norbornene ring-opening metathesis copolymer with a 120° dipyridine ligand is prepared and self-assembled with a 60° or 120° Pt(II) acceptor to fabricate the metallacycle-crosslinked polymer networks. With only 0.28 mol% or less pendant dipyridine units to form the metallacycle crosslinkers, the mechanical properties of the polymers are significantly enhanced. The tensile strengths, Young’s moduli, and toughness of the reinforced polymers reach up to more than 20 MPa, 600 MPa, and 150 MJ/m3, respectively. Controllable destruction and reconstruction of the metallacycle-crosslinked polymer networks are further demonstrated by the sequential addition of tetrabutylammonium bromide and silver triflate, indicative of good stimuli-responsiveness of the networks. These remarkable performances are attributed to the thermodynamically stable, but dynamic metallacycle-based supramolecular coordination complexes that offer strong linkages with good adaptive characteristics.

Modulating the structure and photochromic performance of hybrid metal chlorides with nonphotochromic 1,10-phenanthroline and its derivative.

Hybrid photochromic materias (HPMs), especially crystalline HPMs (CHPMs), have been widely investigated due to their feasibility in maintaining the advantages of each constituent and genearating captivating photomodulated functionality. Metal-organic complexes (MOCs), as promising candidates for fabricating CHPMs, have attracted the interest of researchers. The molecular predesign of ligands plays a crucial role in yielding MOC-based CHPMs with tunable photochromic functionality. Hitherto, a great majority of CHPMs are driven by photosensitive ligands. However, the complicated synthesis and high cost of photosensitive ligands obviously prevent the macro-synthesis and future application of these CHPMs. Thus, it is indispensable to explore novel branches of CHPMs. Herein, we report a series of photochromic solid materials bearing modulated photochromic properties by hybridizing metal chlorides with a nonphotosensitive coplanar dipyridine unit 1,10-phenanthroline (phen) and its derivative 5-chloro-1,10-phenanthroline (5-Cl-phen). The resulting hybrids, [ZnCl2(phen)] (1), [CdCl2(phen)] (2), [PbCl2(phen)] (3), [ZnCl(H2O)(5-Cl-phen)2]Cl·2H2O (4), [Cd2Cl4(5-Cl-phen)2] (5) and [Pb2Cl4(5-Cl-phen)2] (6), exhibit distinct structures from the isolated molecular complexes (1 and 4) to the hybrid chain (2, 3, 5 and 6) because of the distinct coordination mode of central metal ions and chloride ions. After photo-irradiation with a Xe-lamp, all complexes, as expected, exhibited apparent color change because of the photoinduced electron transfer (ET) between coordinated chloride ions (Cl-) as electron donors (EDs) and the coordinated coplanar phen and 5-Cl-phen species as electron acceptors (EAs). More importantly, the photochromic performance of the title complexes could be modulated by phen and 5-Cl-phen. This study provides a general and facile way for modulating the structure and photochromic performance of hybrid metal chlorides with phen or phen-based derivatives under the synergy of crystalline engineering strategy and ET mechanism.

Low band gap polymers based on the electrochemical polymerization of Phenazine: studies on the color changing ability in near-infrared region

In this work, two quinoxline type monomers, 10,14-bis(4-octyl-2-thienyl)-dipyrido[3,2-a:2′,3′-c] [1, 2, 5] thiadiazolo[3,4-i] quinoxaline (OTPTP) and 10,14-bis(4-octyl-2-thienyl)-dibenzo[a, c][1,2,5]thiadiazolo [3,4-i] quinoxaline (OTBTP) were prepared, and the electrochromic features of their polymer films that were synthesized on the ITO glass surface by electrochemical polymerization were studied. The electronic characteristics of two different electron-withdrawing groups and their influences on the electrochemical polymerization of monomers and electrochromic performance of the obtained polymers were observed. The electronic performance of monomers illustrated that OTBTP can be polymerized in the lower potential range than OTPTP due to the stronger electron-withdrawing capability of the electron-withdrawing groups in OTPTP which contains two dipyridine units. The UV Visible NIR spectra analysis showed that both polymers, POTPTP and POTBTP, have one broad absorbance band in the region of 400 ~ 1600 nm at the neutral state. The electrochromic analysis revealed that the two polymer films exhibited reasonable optical contrasts in the infrared region of 1000 ~ 1600 nm with low response time (about 5 s) and low band gap.

Coordination-driven strategy towards crystalline hybrid photochromic materials via the marriage of a non-photochromic extended dipyridine unit and zincophosphate

The coordinative linkage of supramolecular zincophosphate building units and a non-photochromic dipyridine unit generates two hybrid photochromic frames.

Zinc-diphosphonates with extended dipyridine units: synthesis, structures, in situ reactions, and photochromism.

Two zinc-diphosphonates formed from extended dipyridine units di-3,6-(4'-pyridyl)-1,2,4,5-tetrazine (dipytz) and 1,4-di(pyridine-4-yl)benzene (pbyb), [H2-Hdpt][Zn3(HEDP)2(H2O)]·2H2O (1) and [Zn2(HEDP)(pbyb)0.5(H2O)]·H2O (2) were solvothermally prepared (HEDP = 1-hydroxyethylidenediphosphonate, Hdpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole). Compound 1 exhibits an anionic Zn-HEDP layer with protonated dipyridine fragments as the template. In 2, the HEDP ligands bridge Zn2+ ions to form neutral zincophosphonate layers as supramolecular building blocks (SBBs), which are further pillared by neutral pbyb moieties to generate the final 3D pillar-layer structure. Interestingly, in situ reactions have taken place in the formation of 1, and the starting material dipytz in situ transformed to Hdpt in the process of assembly and was captured in the resultant crystal. Although the structural constituents are non-photochromic, 2 features photochromic performance with a detectable color change from colorless to pink under the stimulus of UV light under ambient conditions. A reversible color change process has been realized via annealing the colored sample at 120 °C for half an hour or putting the colored sample in air for two hours.

Synthesis and Properties of Novel Hole-Transporting Materials Containing Triphenylamine and Bipyridine Units

Novel hole-transporting materials (M1, M2) containing triphenylamine and dipyridine units have been synthesized and characterized. Two compounds have excellent solubility in common solvents. The optical, electrochemical and thermal properties of the materials were studied in detail. The results show that two compounds have green emission in dichloromethane, high thermal stability and proper HOMO levels. The properties of compounds M1 and M2 indicate that two compounds are candidates for the application in Organic light-emitting devices as hole-transporting materials.

Zn(II) Coordination by Open-chain Polyamine Ligands Containing Dipyridine Units. Highly Active Dinuclear Zn(II) Complexes in Phosphate Ester Hydrolysis

The synthesis and characterization of two new open-chain ligands, L1 and L2, containing two 2,2'-dipyridine units connected respectively by a pentaethylenhexamine and a pentapropylenhexamine chain, is reported. Zn(II) com- plexation has been studied by means of potentiometric and UV-vis spectrophotometric measurements in aqueous solution. Both ligands form stable mono- and dinuclear complexes, the metal ions being coordinated by a single dipyridine unit and by the adjacent amine groups. The ability of the binuclear Zn(II) complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as substrate. Both complexes display high rate enhance- ments in BNPP cleavage in aqueous solution. The study outlines that different mechanisms are operative in BNPP cleav- age in the presence of the L1 and L2 complexes.

Co(ii) and Cd(ii) complexation with two dipyridine-containing macrocyclic polyamines in water and dimethyl sulfoxide

Solvent effects in the formation of Co(II) and Cd(II) complexes with the two macrocyclic ligands 2,5,8,11,14-pentaaza[15]-[15](2,2′)[1,15]-bipyridylophane (L1) and trimethyl-5,8,11-2,5,8,11,14-pentaaza[15]-[15](2,2′)[1,15]-bipyridylophane (L2), both containing dipyridine units, were analysed by determining the thermodynamic parameters (logK, ΔH°, TΔS°) for the complexation reactions in water and dimethyl sulfoxide (DMSO) by means of potentiometric, spectrophotometric and calorimetric techniques. N-Methylation leads to different solvation properties of the ligands and to different abilities in stabilizing metal complexes via the formation of M–NH⋯S hydrogen bonds to solvent molecules (S) which enhances the σ-donating properties of the donor atom. In contrast to expectations based on the stronger solvation of Cd(II) and Co(II) in DMSO than in water, complexes with L1 display higher stability in DMSO than in water, indicating that ligand solvation, instead of metal ion solvation, plays a major role in determining the stability of L1 complexes in the two solvents. On the other hand, for ligand L2, in which tertiary amino groups are present, an almost opposite trend of stability is observed. Because L2 is less solvated than L1 in water and tertiary nitrogens are weaker bases in DMSO than in water, the stronger solvation of metal ions in DMSO prevails in determining the stability of L2 complexes. Semi-empirical calculations were also performed to obtain some structural information in the gas phase.

Zn(II) coordination to polyamine macrocycles containing dipyridine units. New insights into the activity of dinuclear Zn(II) complexes in phosphate ester hydrolysis.

Zn(II) binding by the dipyridine-containing macrocycles L1-L3 has been analyzed by means of potentiometric measurements in aqueous solutions. These ligands contain one (L1, L2) or two (L3) 2,2'-dipyridine units as an integral part of a polyamine macrocyclic framework having different dimensions and numbers of nitrogen donors. Depending on the number of donors, L1-L3 can form stable mono- and/or dinuclear Zn(II) complexes in a wide pH range. Facile deprotonation of Zn(II)-coordinated water molecules gives mono- and dihydroxo-complexes from neutral to alkaline pH values. The ability of these complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as a substrate. In the dinuclear complexes the two metals play a cooperative role in BNPP cleavage. In the case of the L2 dinuclear complex [Zn(2)L2(OH)(2)](2+), the two metals act cooperatively through a hydrolytic process involving a bridging interaction of the substrate with the two Zn(II) ions and a simultaneous nucleophilic attack of a Zn-OH function at phosphorus; in the case of the dizinc complex with the largest macrocycle L3, only the monohydroxo complex [Zn(2)L3(OH)](3+) promotes BNPP hydrolysis. BNPP interacts with a single metal, while the hydroxide anion may operate a nucleophilic attack. Both complexes display high rate enhancements in BNPP cleavage with respect to previously reported dizinc complexes, due to hydrophobic and pi-stacking interactions between the nitrophenyl groups of BNPP and the dipyridine units of the complexes.

A thermodynamic and spectrophotometric study of anion binding with a multifunctional dipyridine-based macrobicyclic receptor

Synthesis and characterisation of a new macrobicycle containing two dipyridine units ( L) is reported. Protonated forms of L are efficient receptors for inorganic phosphate and nucleotide anions. The binding properties of L toward these substrates have been investigated in aqueous solution by means of potentiometric, microcalorimetric and 1H NMR measurements. Only 1:1 receptor–anion complexes have been found in solution. The stability of the adducts with inorganic phosphates anions is higher than that found for the nucleotides complexes. The complexation reactions are endothermic, and promoted by invariably favourable entropic contributions, indicating that these pairing processes are mostly determined by the desolvation of the interacting species that occurs upon charge neutralisation.

Cu(ii) and Ni(ii) complexes with dipyridine-containing macrocyclic polyamines with different binding unitsElectronic supplementary information (ESI) available: selected bond lengths [Å] and angles [°] for [CuL1](ClO4)2 (Table S1) and for [NiL1](ClO4)2 (Table S2); absorption spectra of L2 in the presence of Cu(ii) (1 ∶ 1 molar ratio) at different pH values (Fig. S1). See http://www.rsc.org/suppdata/dt/b2/b211904h/

The coordination features of the two dipyridine-containing polyamine macrocycles 2,5,8,11,14-pentaaza[15]-[15](2,2′)[1,15]-bipyridylophane (L1) and 4,4′-(2,5,8,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane) (L2) toward Cu(II) and Ni(II) have been studied by means of potentiometric and spectrophotometric UV-vis titrations in aqueous solutions. While in L1 all the nitrogen donor atoms are convergent inside the macrocyclic cavity, in L2 the heteroaromatic nitrogen atoms are located outside. Ligands L1 and L2 form stable mono- and dinuclear complexes with Cu(II). In the case of Ni(II) coordination, only L1 gives dinuclear complexes, while L2 can form only mononuclear species. In the Cu(II) or Ni(II) complexes with L1 the metal(s) are lodged inside the macrocyclic cavity, coordinated to the heteroaromatic nitrogens. As shown by the crystal structure of the [CuL1]2+ and [NiL1]2+ cations, at least one of the two benzylic nitrogens is not coordinated and facile protonation of the complex takes place at neutral or slightly acidic pH values. The particular molecular architecture of L2, which displays two well-separated binding moieties, strongly affects its coordination behavior. In the mononuclear [CuL2]2+ complex, the metal is encapsulated inside the cavity, not coordinated by the dipyridine unit. Protonation of the complex, however, occurs on the aliphatic polyamine chain and gives rise to translocation of the metal outside the cavity, bound to the heteroaromatic nitrogens. In the [NiL2]2+ complex the metal is coordinated by the dipyridine nitrogens, outside the macrocyclic cavity. Thermodynamic and/or kinetic considerations may explain the different behavior with respect to the corresponding Cu(II) complex.

A new dipyridine-containing cryptand for both proton and Cu(ii) encapsulation. A solution and solid state study

Synthesis and characterization of the new polyamine cryptand 2,5,8-triaza-5-methyl-2,8-(N-methyldipropylamino)[9]-2,2′-dipyridinophane (L) and its macrocyclic precursor 2,5,8-triaza-5-methyl[9]-2,2′-dipyridinophane (L1) are reported. Ligand L1 contains a diethylenetriamine chain linking the 6,6′ positions of a 2,2′-dipyridine moiety; in L an N-methyldipropylamine bridge links the two benzylic nitrogens of L1. Protonation and Cu(II) coordination have been studied in aqueous solution by means of potentiometric and UV-vis spectrophotometric measurements. Considering proton binding, cryptand L behaves as a proton sponge, i.e., the first protonation constant is too high to be measured in aqueous solution. Both ligands form 1 ∶ 1 Cu(II) complexes in aqueous solutions. The crystal structure of [CuL1]2+ reveals that the metal is coordinated by the five ligand donors in a strongly distorted square pyramidal geometry. Almost the same coordination environment is found in the protonated complex with L, [CuLH]3+, while the nitrogen of the N-methyldipropylamine bridge is protonated. In marked contrast, in the [CuL]2+ complex this nitrogen is involved in metal coordination. Both the solution and structural results account for the high rigidity of the macrocyclic moiety of L defined by the dipyridine unit and the diethylenetriamine chain, while coordination of the more flexible N-methyldipropylamine unit is modulated by complex protonation.

Formation of A2B2 supramolecular porphyrin co-polymers.

New supramolecular A2B2 co-polymers formed in solution from a rigid diporphyrin monomer (the A2 unit) and a short flexible dipyridine monomer (the B2 unit) are reported; NMR experiments show that complete binding occurs at mM concentrations; UV titrations reveal that the dipyridine unit and a monomeric control ligand have identical binding constants, confirming that linear polymers were generated (in preference to small cyclic oligomers); at 2 x 10(-2) M polymers with an average molecular weight of 17,100 g mol-1 and containing approximately 14 porphyrin units have formed.

Coordination properties of a polyamine cryptand with two different binding moieties. A case of a pH-modulated antenna device based on a new Eu(III) cryptate complex.

Protonation and alkali- and alkaline-earth-metal coordination by the dipyridine-containing cryptand L have been studied by means of potentiometric and spectroscopic (UV-vis, (1)H NMR) measurements in aqueous solutions. This ligand is constituted by an aliphatic polyamine chain and a coordinating cleft, delimited by two dipyridine units, where the metal ion is lodged. The resulting complexes are characterized by an unusually high stability. The polyamine chain is not involved, or weakly involved, in metal coordination, and facile protonation can occur on the nitrogen atoms of this moiety. Similar coordination features are found in the Eu(III) complex. A fluorescence emission study reveals that the Eu(III) cryptate shows the characteristic visible emission of the metal, due to the intramolecular energy transfer to the metal ion mainly from the lower energy triplet state of the cryptand. On the other hand, the emission intensity is modulated by pH, giving a maximum at neutral pH and decreasing at both acidic and alkaline pH values.

Protonation and Zn(II) coordination by dipyridine-containing macrocycles with different molecular architecture. A case of pH-controlled metal jumping outside-inside the macrocyclic cavity.

The synthesis of the macrocyclic ligand 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridylophane (L3), which contains a pentaamine chain linking the 4,4'-positions of a 2,2'-dipyridine moiety, is reported. Protonation and Zn(II) complexation by L3 and by macrocycle L2, containing the same pentaamine chain connecting the 6,6'-positions of 2,2'-dipyridine, were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. While in L2 all the nitrogen donor atoms are convergent inside the macrocyclic cavity, in L3 the heteroaromatic nitrogen atoms are located outside. Both ligands form mono- and dinuclear Zn(II) complexes in aqueous solution. In the mononuclear Zn(II) complexes with L2, the metal is coordinated inside the macrocyclic cavity, bound to the heteroaromatic nitrogen donors and three amine groups of the aliphatic chain. As shown by the crystal structure of the [ZnL2](2+) complex, the two benzylic nitrogens are not coordinated and facile protonation of the complex takes place at slightly acidic pH values. Considering the mononuclear [ZnL3](2+) complex, the metal is encapsulated inside the cavity, not coordinated by the dipyridine unit. Protonation of the complex occurs on the aliphatic polyamine chain and gives rise to translocation of the metal outside the cavity, bound to the heteroaromatic nitrogens.