•Luminescent pyrene-functionalized nano-SiO2Pyr hybrids were prepared.•A 1- to 2- nm thick organic functionalization layer on nano-SiO2 was observed.•Formation of pyrene excimer was concentration and solvent polarity dependent.•Dynamic fluorescence decay was investigated in solutions and doped thin films.Luminescent pyrene-functionalized nano-SiO2 (nano-SiO2Pyr) hybrids were synthesized and characterized using thermogravimetry, infrared, UV–vis absorption and, X-ray photoelectron spectroscopy, as well as field emission transmission electron microscopy (FETEM). The organic substituents immobilized on the nano-SiO2Pyr hybrids accounted for approximately 10% of the total weight. Polyethylene glycol 200 (PEG200) was found to be the most suitable solvent to suspend the nano-SiO2Pyr hybrids compared to other commonly used organic solvents. FETEM images indicated an average SiO2 nanoparticle diameter of approximately 12 nm and a 1- to 2-nm thick organic species functionalization layer. Several emission peaks were recorded at wavelengths of 380–580 nm and were designated as emissions arising from either the monomer or excimer of the pyrene substituents. Excimer formation was concentration and solvent polarity dependent, with higher concentrations and a stronger solvent polarity benefiting excimer formation. Further, nano-SiO2Pyr hybrids were doped in poly(methyl methacrylate) (PMMA) thin films; fluorescence spectra indicated that the excimer could be formed almost exclusively from neighboring nano-SiO2Pyr hybrids. Time-resolved fluorescence decays revealed that the emission lifetimes of nano-SiO2Pyr monomers and excimers were approximately 190 ns and 65–100 ns in the PEG200 solution, respectively, which was shortened to 0.45 ns to tens of ns in doped PMMA thin films, depending on the nano-hybrid concentration. Thus, the present study not only provides a method to prepare luminescent nano-materials but also a route to investigate excimer formation in solutions and thin films.

Terpyridine- (TPy-) functionalized silica nanolinkers (nanoSiO2–TPy) have been prepared and used as nanoscale multidentate ligands to coordinate with the transition metal ions (Mn+ = Zn2+, Fe2+, Tb3+ and Eu3+) for producing luminescent metalated organic–inorganic nanoSiO2–TPyM hybrid materials. Thermogravimetric analysis has revealed that the covalently attached organic species in the nanoSiO2–TPy linkers were about 10% in weight. After they were functionalized with the layers of TPy or TPyM, the as-prepared nanoSiO2–TPy linkers and nanoSiO2–TPyM hybrids formed aggregates more easily due to an increase of internanoparticle interactions. The ζ-potential of the nanoSiO2–TPy linkers was about 34.6 mV, which increased to 55 to 60 mV for the nanoSiO2–TPyM hybrids in the poly(ethylene glycol) 200 (PEG 200) solutions. Under UV radiation, the nanoSiO2–TPy linkers gave off an emission at about 366 nm (monomer of the linkers) in the PEG 200 solutions with the concentrations below 0.5 mg/mL, which shifted to 374 nm after formation of the nanoSiO2–TPyM hybrids. The excimers of the nanoSiO2–TPy linkers and nanoSiO2–TPyM hybrids can be formed in the PEG 200 solutions with concentrations over 1.0 mg/mL and in solid powders. After the excimer was formed, the energy transfer efficiency from the excited states of the nanoSiO2–TPy linkers to the central lanthanide ions was largely enhanced. This resulted in strong luminescent emissions from the ions between 480 and 650 nm, designated to the electron transitions 5D4 → 7Fn (n = 3, 4, 5, 6) and 5D0 → 7Fn (n = 0, 1, 2) of the Tb3+ and Eu3+ ions, respectively.

•Viologen-functionalized core-shell silica nano-composites were prepared.•Nano-composites can be strongly adsorbed on the electrode surface.•Nano-composites showed reversible viologen redox and electrochromic behaviors.•Violet viologen nano-composites could be separated by centrifugation.Electroactive viologen-functionalized silica core-shell nano-composites have been prepared and characterized using thermogravimetry, field emission transmission electron microscopy, and infrared, UV–vis absorption, and X-ray photoelectron spectroscopy. The viologen monolayer functionalized nano-silica core (nano-SiO2VBen) was obtained via a substitution reaction of propylamine−modified silica nanoparticles (nano-SiO2NH2) with N,N'-di(bromomethylbenzyl)-4,4'-bipyridium dibromide (VBenBr2). The nano-SiO2VBen core was positively charged and could thus act as a support for the construction of the shell layer of viologen multilayers through, alternatively, the electrostatic adsorption of poly(sodium-p-styrenesulfonate) (PSS) and VBenBr2. Dynamic light scattering and morphological studies revealed that the dynamic sizes of the nanoparticles increased in the following order: nano-SiO2NH2, nano-SiO2VBen, and nano-SiO2VBen@(PSS/VBen)n. This was due to the assembly of organic multilayers around the nanoparticles and formation of aggregates. Cyclic voltammograms of nano-SiO2VBen- and nano-SiO2VBen@(PSS/VBen)n-modified electrodes showed two couples of redox waves in the potential range from 0 to −1.2 V (vs Hg/Hg2Cl2), corresponding to the redox processes of viologens in the nano-composites. Compared to their precursor of VBenBr2, the nano-SiO2VBen and nano-SiO2VBen@(PSS/VBen)n composites could be more strongly adsorbed on the electrode surface without co-adsorption of the polymeric supporter (Nafion), which can be attributed to a stronger molecular interaction between the present nano-composites and electrode surfaces. Finally, the redox-induced electrochromic properties of VBenBr2 and nano-composites were investigated in the solutions or polymer gel electrolytes, and the results suggest that both viologen organic electrolyte and nano-composites could act as potential candidates for the development of redox-based electrochromic indicators and displays.Download high-res image (204KB)Download full-size image

Electroactive nanocomposites composed of phosphomolybdic acid (PMA) and viologen-functionalized carbon nanotubes were synthesized and used as heterogeneous catalysts for the electrocatalytic reduction of bromate. Viologen (V) was first covalently anchored on the surface of multi-walled carbon nanotubes (MWNTs) to produce positively charged MWNT-V polyelectrolyte, which was then combined with PMA through electrostatic interaction to form MWNT-V@PMA nanocomposites. Thermogravimetric analysis revealed that the organic species in the MWNT-V polyelectrolyte was about 30% in weight. Composition, structure, and morphology of the nanocomposites were investigated by using UV-vis, infrared, Raman and X-ray photoelectron spectroscopy as well as field emission transition electron microscope. The thickness of organic substituents, viologen, and PMA in the nanocomposites was approximately 10 nm covered on the surface of MWNTs. Cyclic voltammogram measurements for the casting films of MWNT-V@PMA nanocomposites revealed four couples of redox waves with cathodic potentials at about −0.56, −0.19, 0.02, 0.21 V, and anodic ones at about −0.46, −0.11, 0.12, 0.31 V (vs Ag/AgCl), respectively, among which the first one corresponded to the electron transfer process of viologens and others to that of the PMA adsorbed. Finally, the MWNT-V@PMA modified electrodes were used as heterogeneous catalysts for the electrocatalytic bromate reduction, which revealed an almost linear correction between the current density and the bromate concentrations in the concentration range from 1 to 15 mmol/l.

•Cinchona alkaloid-terpyridine derivatives and metal complexes were prepared.•Cinchona alkaloid-terpyridine derivatives gave off luminescence at 362 nm.•Ligand excited energy could efficiently transferred to lanthanide ions.•Chirality of terpyridine and metal complexes was induced.We report here the synthesis and spectroscopic properties of two enantiomeric chiral tridentate ligands (TPyCCD and TPyCCN) composed of terpyridine (TPy) and cinchonidine (CCD) or cinchonine (CCN) substituent, as well as their metal complexes with Zn2+, Fe2+, Eu3+, and Tb3+ ions. For the pure ligands, the fluorescent emission intensity increased as their concentrations increased in the dilute solutions, but they decreased when the concentrations were greater than 6.9×10−6 mol/l due to concentration quenching. No significant influence on ligand luminescence was observed for the Zn2+/Fe2+–TPyCCD and –TPyCCN metal complexes. Their lanthanide (Eu3+ and Tb3+) complexes displayed both ligand and lanthanide ion emissions, suggesting that the excited energy of both ligands could be transferred to the central Eu3+ and Tb3+ ions. Mirror-image circular dichroism spectra were recorded, with several signals centered at about 230, 250–270, 296, and 320 nm; the first ones corresponded to the chiral CCD and CCN substituents, while the latter ones corresponded to the TPy substituent and the metal–TPy (M-TPy) coordination units. It is suggested that the chirality of TPy and the metal complexes was induced by the coexisting chiral CCD and CCN substituents. In addition, due to formation of the metal complexes, the relative intensity of the chiral signals of M–TPy coordination units was enhanced at about 320 nm.

•Tetraruthenated porphyrin/phosphomolybdic acid triad hybrids were prepared.•Six reversible redox waves corresponded to TPyP, Rubpy complex and PMA.•TPyP-Rubpy/PMA hybrids were used as photo-catalyst for degradation of organic dye.•TPyP-Rubpy/PMA hybrids used as light-harvesting units for photocurrent generation.Triad hybrid multilayers composed of tetrapyridylporphyrin (TPyP), bis(2,2′-bipyridyl)ruthenium chloride [Ru(bpy)2Cl2], and phosphomolybdic acid (PMA) have been prepared at the gas-liquid interface. The tetraruthenated porphyrin of TPyP-Rubpy complex was synthesized by the coordination interaction of TPyP with Ru(bpy)2Cl2. Surface pressure–area isotherms indicated that the average molecular area of the TPyP-Rubpy complex was in the range of 3.1–3.3 nm2 when the PMA concentration was 0.1–0.3 mg/mL in the subphases. Monolayers of the TPyP-Rubpy/PMA triad hybrids were transferred onto the substrate surfaces by using the Langmuir-Blodgett (LB) method. The absorption spectra of the hybrid LB films revealed several strong peaks between 300 and 440 nm, attributed to the π–π* electron transfer of the Rubpy substituent and the Soret band of TPyP. Under radiation, the TPyP-Rubpy complex gave off strong luminescence in the wavelength between 600 and 700 nm, attributed to the emissions from the Rubpy and TPyP substituents. These emissions largely weakened in the LB films of TPyP-Rubpy/PMA triad hybrids. Cyclic voltammograms showed six couples of redox waves in the potential range from −1.2 to 0.6 V (vs Hg/HgCl2), which could be designated for the electron transfer processes of TPyP, Rubpy and PMA, respectively. Finally, it was revealed that the present triad hybrid LB films can be used as efficient light-harvesting units for the photo-catalytic oxidation of organic dyes and for light-induced photocurrent generation.

A silylated-terpyridine (SiTPy) derivative was newly synthesized and reacted with various transition metal ions in the solutions and self-assembled monolayers (SAMs). Composition and morphology of the SAMs were characterized by using absorption spectra, X-ray photoelectron spectra and atomic force microscope. The silylated-TPy compound gave off a luminescent emission at about 456 nm, which slightly shifted to 452 nm in the Zn2+-SiTPy and Fe2+-SiTPy metalated complexes. The absorbed energy can be further transferred to lanthanide ions (Tb3+ and Eu3+) to give off the typical emissions of the lanthanide complexes together with an emission of the silylated-TPy at about 363 nm.A silylated-terpyridine derivative was synthesized and assembled on the substrate surface. Coordination of the ligand with the transition metals ions and their luminescent properties were investigated in the solutions and self-assembled monolayers.

•Chiral supramolecular porphyrin aggregates were induced by dibenzoyl tartaric acids.•Chirality of the dibenzoyl tartaric acids remained in the LB films.•Irregular nanowires formed for ternary aggregates composed of CdCl2, tartaric acids and porphyrin.•Coordination bonding effectively induced formation of chiral porphyrin aggregates.Enantiomeric dibenzoyl tartaric acid (DBTarA)-induced formation of chiral tetrakis(4-carboxyphenyl)porphyrin (TCPP) aggregates have been investigated in solutions and at the air–water interface. Surface pressure–area isotherms of the monolayers, UV–vis, and infrared spectra, as well as X-ray photoelectron spectra of the transferred Langmuir–Blodgett (LB) films, indicated that, though the small DBTarA molecules had difficulty forming insoluble monolayers at the interfaces, they could insert themselves in the matrix of porphyrins to form TCPP-DBTarA mixed monolayers and LB films. The inorganic salt of CdCl2 in the subphase could stabilize the mixed monolayers due to formation of the coordination bond between Cd(II) ions and carboxylic acid substituents of TCPP and DBTarA. Mirror-imaged circular dichroism spectra were recorded with two signals centered at about 230–250 and 400–450 nm; the former indicated that chirality of the DBTarA remained in the LB films while the latter (corresponding to the Soret absorption band of porphyrins) indicated that the co-existing DBTarA could induce the formation of supramolecular chirality in the porphyrins. It was revealed that pure TCPP formed dot-like aggregates while its mixtures with DBTarA formed irregular nanowires on the CdCl2 subphase surface, a phenomenon which may be attributed to the fact that the coordination bond of CdOOC connects TCPP and DBTarA molecules to form larger one-dimensional ternary molecular assemblies.

A metal-directed assembling approach has been developed to encapsulate hydrogenase (H2ase) within a layer-by-layer (LBL) multilayer of carbon nanotube polyelectrolyte (MWNT-PVPMe), which showed efficient biocatalytic oxidation of H2 gas. The MWNT-PVPMe was prepared via a diazonium process and addition reactions with poly(4-vinylpyridine) (PVP) and methyl iodide (MeI). The covalently attached polymers and organic substituents in the polyelectrolyte comprised 60–70% of the total weight. The polyelectrolyte was then used as a substrate for H2ase binding to produce MWNT-PVPMe@H2ase bionanocomposites. X-ray photoelectron spectra revealed that the bionanocomposites included the elements of Br, S, C, N, O, I, Fe, and Ni, which confirmed that they were composed of MWNT-PVPMe and H2ase. Field emission transmission electron microscope images revealed that the H2ase was adsorbed on the surface of MWNT-PVPMe with the domains ranging from 20 to 40 nm. Further, with the use of the bionanocomposites as nanolinkers and Na2PdCl4 as connectors, the (Pd/MWNT-PVPMe@H2ase)n multilayers were constructed on the quartz and gold substrate surfaces by the Pd(II)-directed LBL assembling technique. Finally, the as-prepared LBL multilayers were used as heterogeneous catalysts for hydrogen oxidation with methyl viologen (MV2+) as an electron carrier. The dynamic processes for the reversible color change between blue-colored MV+ and colorless MV2+ (catalyzed by the LBL multilayers) were video recorded, which confirmed that the H2ase encapsulated within the present LBL multilayers was of much stronger stability and higher biocatalytic activity of H2 oxidation resulting in potential applications for the development of H2 biosensors and fuel cells.

Multi-pyridine functionalized multi-walled carbon nanotubes (MWNTs) have been prepared via a highly active “mediator” of benzyl bromide modified-MWNTs, which can act as versatile nano-linkers to design and construct various metal–organic nanomaterials.

•Pd(II)-directed chiral metal–organic complex LBL multilayers were constructed at interface.•The LBL multilayers gave off luminescent emission at about 365 nm.•The LBL metal-complex multilayers showed complex chirality and quasi-reversible redox behavior.Palladium(II)-directed chiral metal–organic complex multilayers have been prepared on substrate surfaces through a layer-by-layer (LBL) assembly using hydroquinine anthraquinone-1,4-diyl diether bidentate ligands as linkers. The assembling process was monitored by measuring UV–vis absorption and X-ray photoelectron spectra, as well as scanning electron and atomic force microscopy after each layer. It was shown that the molecular chirality of the ligands was retained in the metal–organic complex multilayers. The LBL multilayer fluorescence spectrum showed a broad band at approximately 365 nm corresponding to the emission from the excited hydroquinine substituents. Cyclic voltammograms revealed a quasi-reversible redox wave couple with cathodic and anodic potentials of −0.35 and −0.05 V (vs. Ag/AgCl) at a potential scan rate of 0.05 V/s, which could be assigned to the redox reaction of metal–organic complexes in the multilayers. Further, the redox potential and the potential separation between cathodic and anodic peaks closely depended on the potential scan rate due to the strong film resistance caused by the closely packed arrangement of the metal–organic complexes in the LBL multilayers.

Metal-bisterpyridine coordination polymers (CPs) have been synthesized at the air–water interface through an interfacial coordination reaction of metal ions (Zn2+/Fe2+) with bidentate ligand of 4,4′′′′-(1,4-phenylene)bis(2,2′:6′2′′-terpyridine) (PBTerpy). Surface pressure-area isotherms indicated that the average molecular area of PBTerpy was about 0.8 nm2 on the pure water surface, which slightly increased to about 1 nm2 on the inorganic salt subphase surfaces due to the formation of Zn(Fe)-PBTerpy CPs. Monolayers of the Zn(Fe)-PBTerpy CPs were deposited on the quartz, Si and indium tin oxide (ITO) substrate surfaces by the Langmuir–Blodgett (LB) method. The as-prepared LB films were characterized by using UV-vis absorption and fluorescence spectroscopy, X-ray photoelectron spectroscopy, as well as by using scanning electron microscope and atomic force microscope. The pure PBTerpy ligand and its LB films showed a broad fluorescent emission at about 350–370 nm. This emission red shifted to about 380–410 nm in the LB films of Zn(Fe)-PBTerpy CPs. Time-resolved fluorescent spectra revealed that the emission lifetime was about 1.2–2.4 ns for the pure PBTerpy ligand in the dilute methanol solution and its LB films, while it was about 5.0 ns in the LB film of Fe-PBTerpy CPs and 20.6 ns in the LB film of Zn-PBTerpy CPs. A couple of reversible redox wave was recorded and centered at about −0.53 V (vs Ag/AgCl) for the ITO electrode covered by the LB film of Fe-PBTerpy CPs, which was designated to one electron transfer process between the CPs of Fe(II)-PBTerpy and Fe(III)-PBTerpy. Since the PBTerpy can coordinate with lots of transition metal ions, we suggest that the present method may be used to prepare new optically and electrically active organic–inorganic composite materials.Graphical abstractHighlights► Zn(Fe)-bisterpyridine coordination polymers were synthesized at interface. ► The LB films of Zn(Fe)-bisterpyridine were prepared and characterized. ► The coordination polymers gave off fluorescence emission at 380–410 nm. ► The Fe-bisterpyridine LB film showed reversible redox behavior.

Chiral coordination polymers (CPs) have been prepared at the air–water interface by using the ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of 1,4-bis(9-O-dihydroquinidinyl)anthraquinone [(DHQD)2AQN] as linkers and AgNO3 as the connector. Surface pressure–area isotherms indicated that both ligands could form insoluble monomolecular layers on the pure water and AgNO3 subphase surfaces. Compared with the average molecular area on the pure water surface, that of the ligand increased about 10% when its monolayer was formed on the AgNO3 subphase surface due to the formation of Ag-(DHQ)2AQN and Ag-(DHQD)2AQN chiral CPs. These monolayers were deposited on the quartz, Si, and indium tin oxide (ITO) substrate surfaces via the Langmuir–Blodgett (LB) method. The as-prepared LB films were characterized by using UV–vis absorption and fluorescence spectroscopy, circular dichroism and X-ray photoelectron spectroscopy, as well as by using a scanning electron microscope and atomic force microscope. Broad fluorescence emissions were measured at about 365 and 525 nm for the ligands in the methanol solutions. The second emission red shifted to about 555 nm in the LB films of both pure ligands and their Ag-directed CPs. A couple of well-reversible redox waves were recorded and centered at about −0.2 ∼ −0.3 V (vs Ag/AgCl) for the ITO electrode covered by the LB films of (DHQ)2AQN, (DHQD)2AQN, or of the Ag+-directed CPs, which were designated to one electron transfer process of the ligands. Small aggregates were observed for the LB films prepared at the lower surface pressures, which were compressed to form more uniform two-dimensional layers at the higher surface pressures.

Monolayers of a water-soluble metalloporphyrin, manganese tetra-(4-pyridyl) porphine chloride tetrakis (methochloride) (MnTMPyP), and its polymeric derivative with poly (4-vinylpyridine) (MnTMPyP-PVP) have been investigated at the air–water interface. These monolayers were transferred on the substrate surfaces to form hybrid ultrathin films by the Langmuir-Blodgett (LB) method. It was revealed that, although the water-soluble MnTMPyP could not form insoluble monomolecular layer on the pure water surface, it could be stabilized on the NaB(C6H5)4 subphase surface due to an electrostatic interaction between MnTMPyP and B(C6H5)4−, resulting in the formation of MnTMPyP-B(C6H5)4 hybrids. On the other hand, its polymeric derivative of MnTMPyP-PVP could form stable insoluble monolayers on the pure water, NaB(C6H5)4 and Na2PdCl4 subphase surfaces. Composition, structure and microscopic morphology of the as-prepared LB films were characterized by using UV–vis absorption, infrared and X-ray photoelectron spectroscope, as well as scanning electron microscope. The results suggested formation of the hybrid MnTMPyP-B(C6H5)4 and MnTMPyP-(PVP-)B(C6H5)4 and Pd-MnTMPyP-PVP coordination polymer ultrathin films at the interfaces. Cyclic voltammograms of the LB films revealed two couples of reversible redox waves centered at 0.2–0.3 and −0.1 to −0.2 V (vs Ag/AgCl), corresponding to the Mn(II)/Mn(III)TMPyP-(PVP-)B(C6H5)4 and Mn(III)/Mn(IV)TMPyP-(PVP-)B(C6H5)4 electron transfer processes of the manganese porphyrins in the LB films.Highlights► Polymeric manganese porphyrin PVP-MnTMPyP was synthesized. ► PVP-MnTMPyP-B(C6H5)4 hybrids were assembled. ► Pd-MnTMPyP-PVP coordination polymer multilayers were prepared. ► The hybrid and coordination polymer multilayer modified electrode showed reversible redox reaction.

Pd(II)/Fe(II)-mediated three-dimensional bimetal-organic multilayers have been constructed on the substrate surfaces with the use of a polymeric ligand of terpyridine-contained poly(vinylpyridine) (PVPTPy) derivative as a linker as well as inorganic salts of Na2PdCl4 and Fe(BF4)2 as connectors. The assembly process was monitored by measuring the absorption spectra, which revealed two main absorption bands at wavelengths of 250∼340 nm and about 580 nm corresponding to the electron transition of pyridyl or terpyridyl substituents as well as metal–ligand charge transfer, respectively. X-Ray photoelectron spectra revealed that the multilayer of (Pd)Fe-PVPTPy was composed of the elements of B(1s), Cl(2p), C(1s), Pd(3d), N(1s), O(1s), F(1s) and Fe(2p), which confirmed formation of the bimetal-organic multilayers. Morphologies of the multilayers were characterized by using scanning electron microscope and atomic force microscopy. Cyclic voltammograms revealed a couple of irreversible redox waves with cathodic peaks appearing in the potential range from −0.2 to −0.4 V (vs. Ag/AgCl), which related to the scan rates and layer numbers of the multilayers. This redox wave was designated as one electron transfer of Fe(II)-PVPTPy/Fe(III)-PVPTPy in the multilayers. The current density of the redox wave decreased with increasing layer numbers of the films due to an increase of the film resistance. Both the polymeric ligand and its bimetal-organic multilayers showed a broad emission at wavelengths of 390∼450 nm. A red shift for the maximum emission band was recorded in the (Pd)Fe-PVPTPy films. Because the transition metal ions can selectively coordinate with either pyridyl or terpyridyl coordinative site, the present method may be developed to design and construct the desired multi-functional metal–organic hybrid materials.

Multiwalled carbon nanotubes (MWNTs) have been functionalised with 5-aminoisophthalic acid in an aqueous solution through an environmentally friendly diazonium-based process. The as-prepared isophthalic acid (IPA)-modified MWNT (IPA-MWNT) hybrids became more easily suspended or dissolved in water. The relative content of the covalently attached IPA substituents was about 7–9% (w/w) in the hybrids. Field emission transmission electron microscopic images revealed that the thickness of the IPA layer was about 1–2 nm. These IPA-MWNT hybrids were used as an alternative layer to construct three-dimensional thin films with a positively charged poly(p-xylylviologen) (PXV) derivative by the layer-by-layer (LBL) method. The assembling process was monitored by using UV–vis absorption spectra and cyclic voltammograms, which indicated an increase of the absorption intensity or redox current intensity after each assembly of the polyelectrolyte. X-ray photoelectronic spectra indicated that the IPA-MWNTs/PXV multilayer was composed of the elements of C(1s), N(1s), and O(1s), which were from either the functionalised IPA-MWNTs or PXV. Finally, it was revealed that the IPA-MWNT hybrids randomly arranged on the substrate surface; the film thickness increased with layer numbers of the LBL films.Graphical abstractHighlights► Isophthalic acid-functionalised carbon nanotube hybrids were prepared. ► Multilayers of the functionalised nanotubes and poly(viologen) were assembled. ► The multilayer modified electrode showed reversible redox properties of viologens.

Polymeric zinc porphyrin derivatives have been synthesized through an axial coordination reaction of zinc tetra(pyridylporphyrin) chloride tetrakis(methochloride) (ZnTMPyP) with poly(4-vinylpyridine) (PVP). The molar fractions of ZnTMPyP relative to pyridyl substituents of PVP in the as-prepared ZnTMPyP-PVP polymers were 1:30 and 1:250. Palladium (II) directed Pd/ZnTMPyP-PVP coordination polymer multilayers were constructed on the quartz and gold substrate surfaces by the layer-by-layer (LBL) method with the use of Na2PdCl4 as the connector and the polymeric zinc porphyrins as the linkers. Compositions, film structure and morphologies of the LBL multilayers were characterized by using UV–vis absorption, X-ray photoelectron spectroscope, scanning electron microscope and atomic force microscope. The fluorescence emission properties of the porphyrins in the LBL multilayers were similar to those in the methanol solutions. The emission lifetime was about 1.36 and 0.16 ns for the zinc porphyrins in the ZnTMPyP-PVP30 solution and LBL multilayers, respectively. It was revealed that the present Pd/ZnTMPyP-PVP LBL multilayers could be used as heterogeneous photocatalyst for the degradation of methyl orange under irradiation at room temperature. Because the multilayers were anchored on the substrate surface through covalent and coordinative bonding, they were of high stability, good recyclability, and facile separation from the reaction system.Graphical abstractHighlights► Two polymeric zinc porphyrins were synthesized. ► Metal-mediated Pd/ZnTMPyP-PVP multilayers were constructed and characterized. ► Immobilized Pd/ZnTMPyP-PVP multilayers were used as heterogeneous photocatalyst.

The metal-mediated self-assembly of coordination polymers, building blocks, and metal–organic frameworks has been widely used to construct multifunctional novel materials on the molecular level. Here, we developed this technique to build up multilayers of functionalized carbon nanotubes on the basis of both intermolecular electrostatic and coordinative interactions. Positively charged electroactive viologenthiol (VSH) was first immobilized on multiwalled carbon nanotubes (MWNTs) to form MWNT–VSH hybrids with a relative content of ∼9% by weight. Field emission transmission electron microscopy images revealed that the VSH molecules randomly covered the surfaces of MWNTs with a thickness of 1 to 2 nm. Then, the MWNT–VSH hybrids were used as nanoscale multidentate “ligands” (linkers) to construct metal-mediated multilayers with the use of CuAc2 as the connectors by the layer-by-layer (LBL) method. The assembly process was monitored by absorption and X-ray photoelectron spectroscopy as well as scanning electron and atomic force microscopy after each assembly of Cu(II) ions and MWNT–VSH hybrids. Finally, the electrochemical behaviors of the viologens in the MWNT–VS/Cu LBL multilayers were investigated.

Triad hybrid multilayers containing the light sensitizers of zinc tetrapyridylporphyrin (ZnTPyP) and pyridine-functionalized TiO2 (TiO2-Py) nanoparticles were constructed on substrate surfaces with the use of Pd(II) ions as the connectors using the layer-by-layer (LBL) method. The assembly process was monitored using ultraviolet–visible (UV–vis) absorption and X-ray photoelectron spectra as well as scanning electron microscopy and atomic force microscopy. The content of the pyridine substituents in the TiO2-Py nanocomposites was about 2% (w/w). The Soret absorption band of ZnTPyP was 24 nm red-shifted in the hybrid multilayers due to a strong intermolecular electronic coupling interaction among porphyrin macrocycles or porphyrin macrocycle/TiO2-Py nanoparticles. The average surface density of each ZnTPyP layer was about 1.4 × 10–10 mol/cm2. Aggregation of the small TiO2-Py nanoparticles to larger domains with sizes up to hundreds of nanometers occurred in the hybrid multilayers; however, such an aggregation behavior was weaker than that in the solutions. The quartz substrate modified with the as-prepared Pd/ZnTPyP/Pd/TiO2-Py triad hybrid multilayers was used as a heterogeneous photocatalyst for the degradation of methyl orange (MO) under irradiation (λ > 420 nm) at room temperature with a catalytic efficiency of about 1.3 × 10–3 MO/ZnTPyP·s. Without the use of the filter, the catalytic efficiency increased because both ZnTPyP and TiO2-Py nanocomposites acted as the light sensitizers. It is suggested that the present heterogeneous catalyst has the advantages of facile separation, high stability, structural controllability on the molecular and nanoscale level, and good recyclability.

Amphiphilic viologens were electrostatically adsorbed on the surface of multiwalled carbon nanotubes (MWCNT) to form viologen–MWCNT hybrids, in which the content of viologens was about 5–10% in weight. Although both viologens and MWCNT hardly dispersed in the water-insoluble organic solvents, the as-prepared viologen–MWCNT hybrids were well dispersed in them with a strong long-term stability, the features of which provided a possibility to prepare their insoluble monolayers at the air–water interface. The surface pressure–area isotherms of these hybrids revealed that they could form stable monolayers, which were transferred on the substrate surfaces by the Langmuir–Blodgett (LB) method. Morphologies of the LB films were characterized by using scanning electron microscopy and atomic force microscopy, the images of which revealed the formation of network two- or three-dimensional films of the functionalized MWCNT. Cyclic voltammograms of the LB films revealed one or two couples of one electron transfer process corresponding to the viologen–MWCNT hybrids with the cathodic and anodic potentials closely related to the alkyl chains of the viologens.Highlights► Amphiphilic viologen–carbon nanotube hybrids were prepared. ► The as-prepared hybrids were well dispersed in organic solvents. ► Two- and three-dimensional network multilayers were constructed and characterized. ► Langmuir–Blodgett films of hybrids showed reversible redox behaviors.

Monolayer behaviors and Langmuir–Blodgett (LB) films of three luminescent aryl triazines, 2,4,6-tri(naphthalen-1-yl)-1,3,5-triazine (TN1Ta), 2,4,6-tri(naphthalen-2-yl)-1,3,5-triazine (TN2Ta), and 2,4,6-tri(anthracen-9-yl)-1,3,5-triazine (TATa) have been investigated. Surface pressure-area isotherms indicated that pure aryl triazines were difficult to form stable monolayers, while their mixtures with arachidic acid (AA) could be stabilized at the air–water interface. The mixed LB films of triazine-AA were deposited on substrate surfaces and analyzed by using UV–vis and infrared absorption spectra, X-ray photoelectron spectra, as well as scanning electron microscopy. Morphologies of the LB films and molecular aggregates were closely dependent on the structure of triazines and the surface pressures of deposition. Under UV radiation, TN1Ta and TN2Ta emitted at 410–460 nm while TATa emitted at 500–510 nm, with the emission lifetime falling into the range of 0.29 to 10.8 ns. Compared with those in solutions, the emissions of aryl triazines were red shifted in the LB films, especially for the TN1Ta-AA and TN2Ta-AA, which was attributed to the closely packed arrangement for the molecules in the LB films.Research Highlights►Luminescent triazine ultrathin films were prepared. ►Hydrogen bond stabilized two-dimensional monolayers. ►Substituents of triazines dominate morphology and phase separation of aggregates. ►Luminescent wavelength and lifetime depend on substituents of triazines.

Palladium-mediated layer-by-layer (LBL) multilayers with poly(4-vinylpyridine) (PVP) as linker have been constructed on quartz substrate surface and characterized by using UV–Vis absorption spectra, attenuated total reflection infrared spectra, X-ray photoelectron spectra as well as scanning electron microscopy. The as-prepared Pd-PVP multilayers modified substrate was used as heterogeneous catalyst for selectively catalytic hydrogenation of aromatic conjugated alkenes at room temperature. Hydrogen gas was used as a reductant for the connectors of Pd(II) ions as well as hydrogen source for the hydrogenation reactions of alkenes. X-ray photoelectron spectra revealed that the connectors of Pd(II) ions could be reduced to Pd(0) atoms by hydrogen saturated aqueous solution. Yields of the hydrogenation reaction were closely related to the nature of aromatic conjugated alkenes. Because the Pd(0) atoms were encapsulated in the matrix of Pd-PVP multilayers and immobilized on the quartz surface, the present Pd-PVP heterogeneous catalysts had the advantages of high stability, good recyclability as well as the advantage of monitoring the catalytic reaction process through immersing in or withdrawing the modified substrate from the reaction solutions.Research highlights► Pd-PVP multilayers were prepared by layer-by-layer method. ► Immobilized Pd-PVP multilayers acted as heterogeneous catalyst. ► Hydrogen used as a reductant for the connectors of Pd(II) ions as well as hydrogen source for the hydrogenation reactions of alkenes. ► The heterogeneous catalyst had advantages of high stability, good recyclability and easy separation.

We reported an interfacial self-assembly of regularly layered porous poly(4-vinylpyridine) (P4VP) films at the interfaces of water–chloroform or –dichloroethane. The porous diameters were in the range from hundred nanometers to several micrometers. It was revealed that formation of such kind of porous materials was solvent dependent. Moreover, cyclic Ag nanoparticles could be grown in the porous P4VP films to form Ag–P4VP nanohybrids under radiation.

Monolayer behaviors of newly synthesized viologens (Vs) containing tolunitrile substituents have been investigated at the air–water interfaces. Surface pressure–area isotherms indicated that these viologens could not form stable monolayers on the surfaces of the subphases of pure water, Fe(BF4)2 and anionic polyelectrolyte of PSS (PSS: poly(styrenesulfonic acid-o-maleic) acid), while they could form insoluble monolayers on the surface of the subphase containing mixtures of Fe(BF4)2 and PSS, which was attributed to the formation of Fe–V metal–organic polyelectrolytes based on an interfacial coordinative reaction between the Fe2+ ions and viologen derivatives. With the use of Langmuir–Blodgett (LB) method, monolayers of Fe–V polyelectrolytes were transferred on the substrate surfaces. X-ray photoelectron spectra indicated that the LB film was composed of the elements of S, C, N, O and Fe, suggesting the formation of Fe–V/PSS hybrid multilayers. Cyclic voltammograms of the viologens revealed two reversible redox couples in the solutions, corresponding to two electron transfers of V2+ ↔ V+ and V+ ↔ V0, respectively. For the indium tin oxide electrode covered by the LB films of Fe–V/PSS, only one broad redox couple was recorded in the potential range of 0 and −1.0 V vs Ag/AgCl, which was attributed to the first redox couple of V2+ ↔ V+. The charger transfer process of viologens in the solutions and Fe–V/PSS multilayers was investigated by the potential chronocoulometry method.Graphical abstractHighlights► New viologens containing tolunitrile substituents were synthesized. ► Fe2+-mediated viologen polyelectrolyte multilayers formed via interfacial coordination reaction. ► Anionic polymer stabilized Fe–viologen polyelectrolyte monolayer and formed hybrid films. ► Fe–viologen hybrid multilayer modified electrode showed reversible redox reaction.

Multilayers of manganese(III) porphyrin-linked poly(vinylpyridinium) (MnTMPyP-PVPMe) polyelectrolyte and poly(styrenesulfonic acid-o-maleic) acid (PSS) have been assembled on gold, quartz, and indium tin oxide surfaces by a layer-by-layer (LBL) technique. The assembly process was monitored by measuring their absorption spectra and frequency change after each assembly, both of which confirmed the formation of three-dimensional MnTMPyP-PVPMe/PSS multilayers. The Soret absorption band of porphyrin red shifted about 8 nm in the multilayer compared with that in the dilute aqueous solution. The average mass changes for each assembly of MnTMPyP-PVPMe and PSS were estimated to be about 2.9 and 0.25 μg/cm2, respectively. X-ray photoelectron spectra revealed that the as-prepared multilayers were composed of S 2p , C 1s , N 1s , O 1s, and Mn 2p , corresponding to polymers of MnTMPyP-PVPMe and PSS. A rough surface was observed after the assembly of MnTMPyP-PVPMe on the gold surface, but it became smoother when the PSS layer was adsorbed. The significant difference in the mass change and film morphology after the assembly of MnTMPyP-PVPMe compared to those after the assembly of PSS was ascribed to the reason that the MnTMPyP-PVPMe polyelectrolyte contained large metalloporphyrin macrocycles, which were axially coordinated to the pyridyl substituents of the PVP polymeric backbones. The cyclic voltammograms revealed two couples of redox waves in the phosphate electrolyte solution at pH 11, which corresponded to the electron-transfer processes of Mn(II)/Mn(III) and Mn(III)/Mn(IV) of polymeric manganese porphyrin MnTMPyP-PVPMe. The charge-transfer process was also investigated. Finally, the present MnTMPyP-PVPMe/PSS multilayers were used as a heterogeneous catalyst for the decoloration of an azo dye.

Hydrogenase (H2ase)–cationic electrolyte biohybrids were assembled at the air–water interface via intermolecular electrostatic interaction. The H2ase used was purified from the phototropic bacterium of Thiocapsa roseopersicina. Two kinds of cationic electrolyte compounds (CECs) were used, the difference of which was whether they contained viologen substituent or not. Surface pressure–area isotherms indicated that these CECs were co-existed with the H2ase in the monolayers, which were then transferred to substrate surfaces to form H2ase–CECs hybrid films by the Langmuir–Blodgett (LB) method. Uniform film was formed when polyelectrolyte was used as the subphase. Cyclic voltammograms (CVs) of the LB films showed a couple of redox waves in the potential range of −0.4 to −0.65 V vs. Ag/AgCl, which was ascribed to one electron process of either [4Fe–4S] clusters of H2ase or viologens of the CECs. A direct electron transfer between the H2ase and electrode surface was achieved in the LB films. Stronger current intensity was recorded when the CV measurements were done in H2 saturated electrolyte solution than that in Ar. It was confirmed that the H2ase biocatalytic activity remained in the LB films. Thus, we suggest that the present H2ase–CECs biohybrids could act as potential materials for the studies of interconversion reaction of H2 and protons.

Pyridylthio-modified multiwalled carbon nanotubes (pythio-MWNTs) have been prepared by a reaction of the oxidized MWNTs with S-(2-aminoethylthio)-2-thiopyridine hydrochloride. The obtained pythio-MWNTs nanocomposites formed stable floating monolayers at the air−water interface, which were transferred onto substrate surfaces by the Langmuir−Blodgett (LB) method. Compositions and morphologies of the LB films were characterized by absorption, Raman, X-ray photoelectron spectra as well as by scan electron microscopy and atomic force microscopy. These pythio-MWNTs LB films were then used as a support to immobilize hydrogenase (H2ase) to form bionanocomposite of pythio-MWNTs-H2ase. Cyclic voltammograms for indium tin oxide electrode covered with the pythio-MWNTs-H2ase films were investigated in both Ar and H2 saturated 0.05 M KCl electrolyte solutions at pH from 4.0 to 9.0. A reversible redox couple of [4Fe−4S]2+/1+ clusters of H2ase was recorded when the pH value was 6.0 and 9.0, with reduction and oxidation potentials appearing at about −0.70 and −0.35 V vs Ag/AgCl, respectively. It was revealed that the H2ase was of high catalytic activity and strong stability in the LB films of pythio-MWNTs-H2ase. Hence, we suggested that the present bionanocomposites could be used as heterogeneous biocatalyst to catalyze reversible reaction between protons and H2, resulting in potential applications in biohydrogen evolution and H2 biofuel cells.

Coordination polymers (CPs) can encapsulate small molecules within their nanosized coordination cages to form hybrid supramolecular materials. We reported here assembly of Pd(II)-mediated CP multilayers on the substrate surfaces by layer-by-layer method with six kinds of multidentate ligands as linkers, which included 4,4′-bipyridyl (BPy), binaphthylbis(amidopyridyl) (BNBAPy), tris(4-pyridyl)-1,3,5-triazine (TPyTa), tetra(4-pyridyl)porphyrin (TPyP), ligand-like complex of Fe(pyterpy)2 (pyterpy: 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine), and poly(4-vinylpyridine) (PVP). The multilayer assembly process was characterized by using UV–vis absorption spectra and X-ray photoelectron spectra. Electrochemical behaviors of the as-prepared CP-modified electrodes were investigated in hexacyanoferrate solution, which revealed well-reversible redox waves of Fe(CN)63−/4− ions for the electrode covered with the Pd–TPyTa or Pd–Fe(pyterpy)2, while irreversible ones for the electrode covered with the Pd–BPy or Pd–PVP. The results indicated that Fe(CN)63−/4− ions could reach electrode surface across the CP multilayers of TPyTa or Pd–Fe(pyterpy)2, which was attributed to the fact that their coordination cages were large enough for the Fe(CN)63−/4− ions to penetrate through. Charge-transfer diffusion coefficient (D) was calculated based on chronocoulomograms of the CP multilayer-modified electrodes. D was in the range from 0.34 × 10−10 to 1.3 × 10−10 cm2/s for the electrodes modified by four layers of Pd–TPyP, Pd–BNBAPy, Pd–TPyTa and Pd–Fe(pyterpy)2, respectively. The present methodology provides a facile way to construct three-dimensional supramolecular materials on the solid surfaces as well as to study the charge-transfer behaviors in artificial membranes.

Metal-mediated coordination polyelectrolyte multilayers with a bisterpyridine ligand (Bisterpy) have been self-assembled at air−water interfaces via coordination reactions of the bidentate ligand Bisterpy with inorganic salts in the subphases. To avoid dissolution of the viologen-like coordination polyelectrolyte monolayers, anionic poly(styrenesulfonic acid-o-maleic) (PSS) acid was added in the subphases as a supporting layer. The average molecular area of the ligand Bisterpy could reach 1.2−1.5 nm2 on the surfaces of the subphases containing mixtures of inorganic salts (M) and PSS, although the ligand was unable to form a stable monolayer on the pure water surface. The Langmuir−Blodgett (LB) method was used to deposit the Bisterpy/PSS and M-Bisterpy/PSS hybrid multilayers on the substrate surfaces, which were characterized by using absorption and fluorescence spectroscopy as well as electrochemical analysis. Quasi-reversible redox waves were recorded and centered at about −0.68 and −0.92 V (vs Ag/AgCl), respectively, corresponding to the two-electron process of the ligand, Bisterpy2+ ↔ Bisterpy•+ ↔ Bisterpy0, which were slightly shifted to lower potentials in the LB films of metal-mediated coordination polymers. The film compositions were determined by using X-ray photoelectron spectroscopy. The as-prepared LB films showed strong stability and good electrochromic response upon the applied potential of −1.1 V vs Ag/AgCl and thus could act as potential materials in the development of redox-based molecular switches and display devices.Keywords: coordination polyelectrolyte; electrochemistry; electrochromic effect; interfacial assembly; Langmuir−Blodgett film

Electrochemical behaviors and catalytic oxidation of nitrite have been investigated by using the indium tin oxide (ITO) electrodes modified by the Langmuir–Blodgett (LB) films of manganese porphyrin and its palladium-mediated multiporphyrin arrays. The multiporphyrin arrays were prepared at the air–water interface. Surface pressure–area isotherms indicated that monolayers of the porphyrin of MnTPyP (TPyP: tetrapyridylporphyrin) could be stabilized on the sodium tetraphenylboron and K2PdCl4 subphase surfaces, but not on the pure water surface. These monolayers were transferred onto quartz and ITO substrate surfaces with the use of vertical dipping method, and characterized by using transmission electron microscope, UV–vis absorption and X-ray photoelectron spectra. For the electrodes modified by the porphyrin LB films, reversible Mn(II)TPyP ↔ Mn(III)TPyP and Mn(III)TPyP ↔ Mn(IV)TPyP redox couples were recorded, and centered at about − 0.17 and 0.52 V vs. Ag/AgCl, respectively. A high-valent Mn(V)TPyP intermediate was detected when the cyclic voltammograms were measured in an electrolyte solution containing sodium nitrite. These multiporphyrin arrays modified electrode showed very strong stability and reproductivity, resulting in potential applications in the development for the nitrite sensors and molecular catalysts of organic compounds.

Molecular assemblies and nanoparticles of chiral coordination polymers composed of connector of K2PdCl4 and linkers of bisdentate binaphthyl-bis(amidopyridyl) (BNBAPy) ligands have been constructed at the air–water interface. The chiral S- and R-BNBAPy ligands showed similar surface pressure–area isotherms on the K2PdCl4 subphase surface, with the limited molecular area of about 1.2 nm2, which suggested that the ligands were nearly parallel to the subphase surface. The X-ray photoelectron spectra for the Langmuir–Blodgett (LB) films of the coordination polymers revealed that the films were composed of Cl, C, Pd and N elements. These Pd-(R-/S-)BNBAPy coordination polymers formed round nanoparticles at the interface with average diameters of 15–20 nm. It was found that the chirarity of ligands was almost remained in the LB films of Pd-(R-/S-)BNBAPy coordination polymers, indicating there was little influence on the orientation or arrangement of the ligand chiral center after the formation of their coordination polymer LB films. The present method could provide a facile way to construct chiral molecular and nanostructural materials.

Multitopic ligand, 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine (pyterpy), has attracted growing attention because of its unique structural features, optical and electrochemical properties. Here, we report spectroscopic studies of pyterpy and its metal complexes in methanol solution. For the pure pyterpy, the ligand emission intensity increased with its concentration in the dilute solution, but decreased when its concentration was over 1.3×10−5 mol/l due to the concentration quenching. No significant influence on the ligand luminescence was observed for the Zn2+-pyterpy complex but strong luminescence quenching was observed for the electroactive Fe2+- and Co2+-pyterpy complexes. The lanthanide (Sm3+, Eu3+ and Tb3+) complexes of the pyterpy showed both ligand and lanthanide ion emissions, especially for the Tb3+-pyterpy complex, suggesting that the excited energy of pyterpy ligand could be efficiently transferred to the central Tb3+ ions. The luminescence was pH sensitive with the strongest emission in the neutral solution. The results indicated that the multitopic ligand of pyterpy could not only act as linkers for the metal-directed building blocks, but also act as optical materials with its own emission at about 364 nm and as light antenna for the lanthanide ions.

Hydrogen evolution was detected in an artificial system composed of light-harvesting unit of purified photosystem I, catalyst of hydrogenase, methyl viologen and electron donor under radiation. Absorption spectral features confirmed that electron transfer from electron donors to proton was via a photoinduced reductive process of methyl viologen.

High-valency manganese (IV,V)-oxo porphyrins have been electrochemically generated and in situ spectrally characterized in multiporphyrin arrays, which were formed by an interfacial coordination reaction of Na2PdCl4 with manganese (III) tetrapyridylporphyrin (MnTPyP). Multilayers of the Pd-MnTPyP multiporphyrin arrays were obtained by the Langmuir−Blodgett (LB) method. The redox behaviors of manganese in the multiporphyrin arrays were pH-dependent. Spectroelectrochemical experiments revealed a reversible redox process between Pd−Mn(III)TPyP and its Mn(IV)-oxo species, but an irreversible process between Pd−Mn(III)TPyP and its Mn(V)-oxo species. The Pd−Mn(IV)TPyP multiporphyrin arrays could be spontaneously reduced to their Mn(III) complex, while the Pd−Mn(V)TPyP arrays were rather stable in basic solutions (pH > 10.5). However, when the Pd−Mn(V)TPyP multiporphyrin arrays were washed by or immersed in water, they were immediately reduced to their Mn(III) complex. Because these well-organized multiporphyrin arrays are of high thermal and chemical stability, they are potential molecular materials in the studies of natural and artificial catalytic processes as well as redox-based molecular switches.

Building blocks of coordination polymers have attracted much attention because of promising applications in porous materials, molecular engineering and devices. We report here an interfacial self-assembly of bimetallic coordination polymer of Cd–Fe(pyterpy)2 (pyterpy: 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine). The surface pressure–area and area–time isotherms indicated that stable monolayers of Fe(pyterpy)2(BF4)2 could be formed on the 0.1 mol/l CdCl2 subphase surface after an interfacial coordination reaction over 12 h. By using the Langmuir–Blodgett (LB) method, monolayers of the Cd–Fe(pyterpy)2 coordination polymer were transferred on the substrate surfaces, and characterized by using the UV–vis absorption and X-ray photoelectron spectroscopy, as well as transition electron microscopy. The spectral data revealed that the LB film was composed of C, Cl, Cd, N and Fe elements, which was in agreement with the composition of the coordination polymer. Reversible redox wave centered at about 500 mV (vs Ag/AgCl) was recorded for the electrode modified with the LB film of the coordination polymer. The present method could be developed to prepare two- and three-dimensional nanoporous building blocks containing two metal ions.

We report the preparation of Langmuir–Blodgett (LB) films composed of oxidized carbon nanotubes (CNTs) and hydrogenase (H2ase) conjugates and their electrochemical properties. Both single-walled (SWNTs) and multi-walled CNTs (MWNTs) were used to form mixed monolayers with H2ase on the Tris–HCl subphase surfaces. By using the LB method, the CNTs–H2ase monolayers were transferred onto CaF2 and indium tin oxide (ITO) electrode surfaces. The LB film modified electrodes showed a couple of waves centered at around −500 mV (versus Ag/AgCl), which corresponding to the redox reaction of [4Fe-4S]2+/1+ clusters in the H2ase. The current intensity was enhanced after co-assembly with CNTs. Because of the different diameters of CNTs, this current intensity was proportional to the scan rate (υ) for the electrodes modified with the LB films of pure H2ase and SWNTs–H2ase, but to the root of scan rate (υ1/2) for those modified with the MWNTs–H2ase LB film. The products of diffusion coefficient and concentration (D1/2C) increased in the order of pure H2ase, SWNTs–H2ase, and MWNTs–H2ase LB films.

We report the HgCl2-mediated interfacial self-assembly of coordination polymer nanocombs composed of (zinc, palladium) tetrapyridylporphyrin and 4,4′-bipyridyl ligands. Scanning electron microscopic images revealed that lengths and widths of the core stems of the nanocombs were about 10 and 1 μm, respectively. Needle-like branches grew out perpendicularly from both sides of the core stems, with branch lengths of about 1–10 μm and diameters of about 0.1–15 μm. Both the X-ray photoelectron spectroscopic and energy dispersive X-ray spectroscopic measurements confirmed that the as-prepared nanocombs were composed of Hg, Cl, C and N elements. When the 4,4′-bipyridyl ligand was replaced by its derivatives, 2,2′-bipyridyl or 4,4′-trimethylenedipyridine, coordination polymer nanocombs could not be obtained. The results revealed that formation of such nanocombs was closely dependent on the structure of the bipyridyl, the mixed molar ratios of porphyrin and 4,4′-bipyridyl, as well as the interfacial reaction time.

Coordination polymer nanotubes have been prepared by using the Hg2+-mediated co-assembly of two ligands, tetrapyridylporphine (TPyP) and tris(4-pyridyl)-1,3,5-triazine (TPyTa), at the water–chloroform interface.

Layer-by-layer (LBL) multilayers of oxidized single-walled carbon nanotubes (SWCNTs) and poly(octylviologen) derivative (POV) have been assembled on gold electrode surfaces. The assembling process was characterized by quartz crystal microbalance (QCM) and electrochemical measurements. The average mass change was about 0.726 and 0.381 μg for each assembly of SWCNTs and POV, respectively. Cyclic voltammograms of the LBL multilayer modified electrodes showed well-reversible redox waves centered at about −640 mV vs Ag/AgCl, corresponding to the normal redox reaction of viologens. These LBL multilayers were very stable in the air and 1 mol/l KCl electrolyte solution. The results of QCM, cyclic voltammograms and chronocoulomograms of the multilayer modified Au electrodes indicated that the oxidized SWCNTs could not only support the formation of stable multilayers but also act as an electron mediator between viologens and electrodes.

Pd-mediated multi-metalloporphyrin arrays have been constructed at the air–water interface. Monolayer behaviors and spectroscopic properties of the arrays closely related to the central ions of metalloporphyrins. It was found that, although oxo[5,10,15,20-tetra(4-pyridyl)porphinato]titanium (TiOTPyP) was unable to form condensed monolayer on the pure water surface, it could be stabilized on the K2PdCl4 subphase surface due to the formation of Pd-TiOTPyP multiporphyrin arrays. Among the three kinds of multiporphyrin arrays investigated, zinc 5,10,15,20-tetra(4-pyridyl)porphine (ZnTPyP) showed largest average molecular area and lowest collapsed surface pressure on the 0.3–0.5 mmol/l K2PdCl4 subphase surfaces. Compared with the absorption spectra in solutions, porphyrin Soret band red shifted in the monolayers and Langmuir-Blodgett (LB) films of multiporphyrin arrays, the extent of this red shift closely related to the central ions of porphyrins. Moreover, fluorescence emissions were partly quenched in the LB films of multi-metalloporphyrin arrays.

Ternary europium complexes were formed at the air–water interface mediated by monolayers of 4,4′-dinonyl-2,2′-dipyridyl (DNDPy) and 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine (MPTPy). A saturated Eu(TTA)3 (TTA: theonyltrifluoroacetone) aqueous solution was used as subphase, on the surface of which condensed DNDPy and MPTPy monolayers could be stabilized. The DNDPy-/MPTPy–Eu(TTA)3 layers were transferred onto either hydrophobic or hydrophilic substrate surfaces by Langmuir–Blodgett (LB) method. Fluorescence spectra showed several sharp peaks corresponding to Eu3+ emissions from 5D1 → 7F1 (535 nm) and 5D0 → 7F0,1,2,3 (580, 595, 612 and 650 nm). A relative stronger emission from 5D1 → 7F1 to that from 5D0 → 7F2 was recorded for the LB films of DNDPy–Eu(TTA)3 complex. Compared with that in solution, longer fluorescence lifetime was observed for the complexes in the LB films.

Cationic poly(viologen) derivatives [(V2+)m] and anionic polymer [poly(styrenesulfonic acid-co-maleic acid), sodium salt] were assembled on electrode surfaces by layer-by-layer (LBL) and Langmuir–Blodgett (LB) methods. The assembling process was in situ investigated by quartz crystal microbalance (QCM) technique. Based on the frequency change, the average surface coverage of poly(butylviologen) in the LBL multilayers is in the range of 1.6∼3.3×10−10 mol/cm2. The mass change for one-layer LB film of poly(dodecylviologen)-anionic polymer is about 44, 96 and 263 ng/cm2 for the films deposited at 5, 10 and 15 mN/m, respectively. The assembled LBL and LB multilayers show well reversible redox characteristics of the viologen. For poly(viologen) with short alkyl chains, the cyclic voltammograms (CVs) show two redox couples of (V2+)m ↔ (V+)m and (V+)m ↔ (0.5(V+)2)m when the last layer is poly(viologen), or one redox couple of (V2+)m ↔ (V+)m when the last layer is anionic polymer. While for poly(viologen) with long alkyl chains, the CVs show only one couple of (V2+)m ↔ (V+)m. The LBL multilayers show much higher stability than the self-assembled monolayers and LB films in electrolyte solution.

We report preparation of organic–inorganic hybrids by using Langmuir monolayers of several alkylammonium derivatives and a viologen cation as templates at the air–water interface. Surface pressure area isotherms indicated that, although the alkylammonium with four long-chains is able to form stable monolayer on the pure water surface, it is difficult to form on the 0.1 mmol/L polyoxometalate (H3PMo12O40) subphase surface; reversely, although the alkylammonium and the viologen with one long-chain unable to form stable monolayer on the pure water surface, it becomes stable on the 0.1 mmol/L H3PMo12O40 subphase surface. The hybrids were transferred onto solid supports by Langmuir–Blodgett (LB) method and characterized by X-ray photoelectron spectroscopy. Electrochemical measurements of the transferred LB films showed reversible three redox couples between 400 and −200 mV for the alkylammonium–polyoxometalate hybrids, and four redox couples between 400 and −520 mV for the alkylviologen–polyoxometalate bifunctional hybrid.

•Carbon nanotube@nano-SiO2BenV(+86-21-65643666)/PMA polynary nanocomposites were prepared.•Functionalized silica nanoparticles covalently attached on the MWNT surfaces.•The nanocomposites showed reversible redox properties of viologen and PMA.•The nanocomposites acted as efficient heterogeneous catalysts for bromate reduction.Organic-inorganic nano-materials have attracted growing attention due to their potential applications for optoelectronic devices, sensors, and heterogeneous catalysts. We reported here on the preparation of polynary nanocomposites composed of poly(4-vinylpyridine) (P4VP) functionalized multi-walled carbon nanotubes (MWNTP4VP), silica nanoparticles (nano-SiO2), viologens, and/or phosphomolybdic acid (PMA), in which the MWNTP4VP, nano-SiO2, and viologens were covalently connected while PMA was electrostatically adsorbed. Thermogravimetric analysis revealed that the nanocomposites were composed of about 40–45% MWNTs, 40–45% nanoSiO2, as well as 10–15% organic species and others. The preparation processes and compositions of the nanocomposites were characterized using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Field emission transmission electron microscopic images revealed that the nano-SiO2BenV particles were strongly attached to the MWNTP4VP surfaces to form MWNTP4VP@nano-SiO2BenV triad nano-cores. Cyclic voltammograms of the MWNTP4VP@nano-SiO2BenV casting films showed three couples of redox waves in the potential range between −0.8 and 0 V (vs Ag/AgCl), designated to the electron transfer process of viologen substituents of MWNTP4VP@nano-SiO2BenV2+ ↔ MWNTP4VP@nano-SiO2BenV+ and their dimers. Further, three couples of redox waves were recorded for the casting films of MWNTP4VP@nano-SiO2BenV/PMA polynary nanocomposites in the potential range between −0.2 and 0.8 V, designated to three successive electron transfer processes of PMA. Finally, it was revealed that the present MWNTPVP@nano-SiO2BenV/PMA polynary composites could act as efficient heterogeneous catalysts for the electrocatalytic reduction of bromate.