Layer-selective epitaxial self-assembly of porphyrins on ultrathin insulators

Copper-Octaethyl Porphyrin self-assembly has been studied on NaCl islands, 1–3 monolayers thick, grown on metal substrates. Extended ordered molecular monolayers are observed for the first time on ultrathin insulator films. The assembly occurs in hierarchical fashion, starting on the metal substrate, then followed by assembly on the first and second NaCl layers, clearly demonstrating a decrease in adsorption energy for increasing insulator layer thickness. The underlying mechanisms are discussed on the basis of molecule–substrate interactions. Voltage-dependent STM images reveal differences of the electronic structure for molecules adsorbed on metal and NaCl/metal areas.     

2-Aminopyrimidine directed self-assembly of zinc porphyrins containing bulky 3,5-di-tert-butylphenyl groups

The 2-aminopyrimidin-5-yl ligand is revealed to be a promising candidate for the construction of supramolecular porphyrin arrays with broad absorption bands for efficient light-harvesting. 10-Mono- and 10,20-di(2-aminopyrimidin-5-yl) derivatives of 5,15-bis(3,5-di-tert-butylphenyl)porphyrin have been synthesized in high yield. Their Zn(II) salts show variable concentration and temperature-dependent UV/vis spectra in solution, consistent with supramolecular aggregation. Whereas the FAB mass spectra of the monosubsituted derivative in toluene suggest the formation of a tetramer at high concentrations and low temperatures (estimated association free enthalpy Delta H = 220 +/- 10 kJ/mol), the larger splitting of the Sorret band (ca. 40 nm) in the variable temperature UV/vis spectra of the disubstituted bis(3,5-di-tert-butylphenyl)porphyrin is indicative of yet higher aggregates involving both 2-aminopyrimidin-5-yl groups. The tetrameric nature of the monosubsituted derivative is confirmed by X-ray analysis, which reveals that two of the 2-aminopyrimidin-5-yl groups are encapsulated by the aggregate and consequently are prevented from undergoing hydrogen bonding. NMR studies show there is no exchange of the 2-aminopyrimidin-5-yl groups, so the tetramer is rigid, which is confirmed by molecular modeling calculations. The tetramer formation is governed by pi-pi interactions, metal coordination, and hydrogen bonding. The di(2-aminopyrimidin-5-yl) derivative forms strongly scattering solutions, which upon standing form green flocculate precipitates, reminiscent of shaken suspensions of bacteriochlorophyll c.     

A convenient preparation of thioether functionalized porphyrins

This paper describes a convenient and high yielding three-step approach for the synthesis of trans-tetraphenylporphyrins possessing two thioethers in the ortho positions, which will facilitate the synthesis of more elaborate and complex porphyrin architectures. Their synthesis is realized by a double nucleophilic aromatic substitution of 2 equiv of a thiolate on 2,6-dichlorobenzaldehyde to generate a bis-thioether substituted benzaldehyde. This aldehyde is then condensed with 2 equiv of pyrrole to give a dipyrromethane, which in the final step reacts with an aromatic aldehyde to give a series of thioether-substituted trans-tetraphenylporphyrins.     

Synthesis and self-assembly of functionalized hexa-peri-hexabenzocoronenes

Monolayers of hexa-alkyl substituted derivatives of hexa-peri-hexabenzocoronene (HBC) 1b have previously been investigated by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). It is expected that different functional groups (electron donating or withdrawing) connected to the aromatic core will influence the packing pattern and possibly the current-voltage characteristics as well. In order to provide suitable model systems, a new synthetic approach to synthesize functionalized HBC derivatives has been developed. This was accomplished by [4 + 2]-cycloaddition of suitably bromo-substituted diphenylacetylenes and 2,3,4,5-tetraarylcyclopenta-2,4-dien-1-ones followed by an oxidative cyclodehydrogenation with iron(III) chloride/nitromethane. Using this strategy three different substitution patterns were synthesized: 2-bromo-5,8,11.14,17-pentadodecylhexa-pecri-hexabenzocoronene (2a), 2,5-dibromo-8,11,14,17-pentadodecylhexa-peri-hexabenzocoronene (2b), and 2,11-dibromo5,8,14,17-pentadodecylhexa-peri-hexa-benzocoronene (2c). These bromo-substituted HBC derivatives were subjected to palladium catalyzed coupling reactions to give donor (alkoxy, amino) as well as acceptor (ester, cyano) substituted derivatives. The self-assembly of these new HBC derivatives was studied in the bulk as well as at an interface. DSC, optical microscopy, and X-ray diffraction revealed the existence of columnar mesophases. The bulk structure in the mesophase is largely insensitive to changes of the substitution pattern; however, in situ scanning tunneling microscopy at the solid-fluid interface between an organic solution of the HBC derivative and highly oriented pyrolytic graphite reveals different packing patterns of the first adsorbed monolayer.     

Polymer-mediated chain-like self-assembly of functionalized gold nanoparticles

We report an easy solution phase template-based method to assemble mercaptoundecanoic acid-functionalized gold nanoparticles (MUA-GNPs) along poly(ethylene oxide) (PEO) chains. Transmission electron microscopy (TEM) images show one-dimensional and two-dimensional chain-like sequences of GNPs resembling PEO chains. The progress of the assembly was monitored by the evaluation of surface plasmon resonance band of MUA-GNPs with time by UV-vis spectroscopy. The assembly process is a result of hydrogen bonding interaction between the ethereal oxygen of PEO and carboxylic acid group of MUA attached to GNPs surface, which was confirmed through FTIR spectroscopy. The interaction between PEO and MUA-GNPs was further confirmed by thermal analysis using differential scanning calorimetry.     

Synthesis and self-assembly of functionalized donor-sigma-acceptor molecules

[structure: see text] 3,5,7-Tris(arylmethyl)-1-aza-adamantanetrione donor-sigma-acceptor compounds have been synthesized in four steps. Computational and (1)H NMR analyses rationalize the solubility, gelation, and conformational properties of the C3-symmetric molecules toward employing sigma-coupled donor-acceptor interactions in molecular self-assembly.     

Evidence for the assembly of carboxyphenylethynyl zinc porphyrins on nanocrystalline TiO2 surfaces

UV-visible absorption and AFM studies suggest that carboxyphenylethynyl zinc porphyrins aggregate on nanocrystalline TiO2 surfaces in an H-type fashion.     

Synthesis of functionalized porphyrins as oxygen ligand receptors

Oxophilic synthetic receptors were designed and synthesized using a porphyrin scaffold, with the aim of constructing a preorganized complementary binding site for phenols and carbohydrates. We pursued three strategies for phenol recognition: (1) Lewis acid/Lewis base combinations serving as a hydrogen bond donor and acceptor for the OH group, (2) Lewis base/pi-pi stacking, targeting both the OH group and the aromatic moiety of phenols, and (3) exchange of the axial hydroxyl ligand on a trivalent and oxophilic metal center of aluminum porphyrin. For the recognition of acidic phenols, the most promising recognition motif was Lewis base/pi-pi stacking, which can bind to phenols with a hydrogen bond and pi-pi stacking interactions. [5-(8-Quinolyl)-10,15,20-triphenylporphyrinato]zinc binds to p-nitrophenol with a binding constant of 540 M(-)(1) in CHCl(3) at 25 degrees C. For carbohydrate recognition, we designed the metalloporphyrin receptor having 8-quinolyl groups and o-carbomethoxymethoxyphenyl groups, where these Lewis basic parts serve as the cooperative hydrogen bonding sites for the hydroxyl groups of glucoside. The receptor binds to beta-octyl glucoside with a binding constant of 7.35 x 10(4) M(-)(1) in CHCl(3) at 15 degrees C, demonstrating importance of formation of a highly ordered hydrogen bonding network between the receptor and the guest. These binding features have significant implications for the rational design of oxophilic artificial receptors.     

卟啉超分子的组装合成及其应用新进展

卟啉超分子已被广泛地用于光学、催化、仿生等方面的研究,部分研究成果已获得实际应用．本文综述了卟啉超分子在组装合成及应用方面的新进展,包括基于不同结构卟啉砌块的新型二维与三维超分子的构筑以及卟啉超分子在光学、催化和分子识别等方面的应用．     

Metal-mediated self-assembly of tetrapyridyl porphyrins by Na+ ions

In the presence of the sodium salt of a bulky anion, which allows the solubility of Na(+) in low polarity solvents, various tetra(4-pyridyl)porphyrin derivatives can spontaneously self-assemble from CH(2)Cl(2) into supramolecular nanostructures exhibiting a long-range order, through the coordination of Na(+) ions by the pyridyl moieties at the macrocycle periphery.     

Transition metal-directed self-assembly of porphyrins bearing redox-active phenylenediamine pendant

Synthesis and Zn(II)-directed self-assembly of the porphyrin-aniline trimer bearing the pyridyl group were demonstrated. Its Au nanoparticle hybrid was also synthesized.     

Pattern recognition of proteins based on an array of functionalized porphyrins

A practical protein-detecting array is desirable for its potential application in proteomics, medical diagnostics, and pathogen detection. Here, we report a novel protein-detecting array based on porphyrins containing peripheral amino acids as protein surface receptors. The array of porphyrin receptors showed a unique pattern of fluorescence change upon interaction with certain protein samples. Both metal and nonmetal-containing proteins and mixtures of proteins gave distinct patterns, allowing their unambiguous identification. The composite pattern for each sample was subjected to principal component analysis (PCA) to generate a clustering map for more practical visualization. Increasing the number of porphyrin receptors from eight to sixteen gave improved resolution, suggesting that this array is expandable to give satisfactory resolution for any given sample system by carefully maximizing the chemical diversity of the receptors.     

Synthesis and properties of functionalized 4 nm scale molecular wires with thiolated termini for self-assembly onto metal surfaces

We report the synthesis of new oligo(aryleneethynylene) molecular wires of ca. 4 nm length scale by palladium-catalyzed Sonogashira cross-coupling methodology. Key structural features are the presence of electron donor 9-(1,3-dithiol-2-ylidene)fluorene (compounds 13 and 14) and electron acceptor 9-[di(4-pyridyl)methylene]fluorene units (compound 16) at the core of the molecules. Terminal thiolate substituents are protected as cyanoethylsulfanyl (13 and 16) or thioacetate derivatives (14). The molecules display well-defined redox processes in solution electrochemical studies. The optical properties in solution are similar to those of the fluorenone analog 6: the strongest absorptions for 6, 13 and 16 are in the region lambda(max) = 387-393 nm, with 13 showing an additional shoulder at 415 nm which is not present for 6 and 16; this shoulder is assigned to a HOMO-LUMO transition from the dithiole to the fluorene unit. Molecules 6, 13, 14 and 16 form self-assembled monolayers on gold substrates which exhibit essentially symmetrical current-voltage (I-V) characteristics when contacted by a gold scanning tunelling microscope (STM) tip. The effects of the chemical modifications at the central unit of 6, 14 and 16 on the HOMO-LUMO levels and electron transport through the molecules in vacuum have been computed by an ab initio approach.     

Coordination-driven self-assembly of truncated tetrahedra capable of encapsulating 1,3,5-triphenylbenzene

The design and synthesis of coordinative truncated tetrahedra is described. The coordination-driven self-assembly of a truncated tetrahedron was achieved using 90° organoplatinum acceptors and a hexapyridyl ligand with six-fold symmetry under mild conditions. This tetrahedron can act as a host toward 1,3,5-triphenylbenzene. The truncated tetrahedral structures and the host-guest complex were identified using multinuclear ((31)P and (1)H) NMR spectroscopy, electrospray ionization mass spectrometry, X-ray crystallography, and pulsed-field-gradient spin-echo NMR, along with computational simulations.     

Coordination-induced branched self-assembly of porphyrins bearing two redox-active phenylenediamine chains

The porphyrins bearing two three-dimensionally regulated oligoaniline chains with terminal pyridyl groups were synthesized. The self-assembled branched polymer complex by introducing Zn(II) to the porphyrin was achieved in solution, which underwent dropcasting on the surface of mica to result in dome-like nanostructures.     

Hierarchical self-assembly of designed 2 x 2-alpha-helix bundle proteins on Au(111) surfaces

Self-assembled monolayers of biomolecules on atomically planar surfaces offer the prospect of complex combinations of controlled properties, e.g., for bioelectronics. We have prepared a novel hemi-4-alpha-helix bundle protein by attaching two alpha-helical peptides to a cyclo-dithiothreitol (cyclo-DTT) template. The protein was de novo designed to self-assemble in solution to form a 4-alpha-helix bundle, whereas the disulfide moiety enables the formation of a self-assembled monolayer on a Au(111) surface by opening of the disulfide, thus giving rise to a two-step self-assembly process. The 2 x 2-alpha-helix bundle protein and its template were studied by X-ray photo electron spectroscopy (XPS), electrochemical methods, and electrochemical in situ scanning tunneling microscopy (in situ STM). XPS showed that the cyclo-DTT opens on adsorption to a gold surface with the integrity of the 2 x 2-alpha-helix bundle proteins retained. The surface properties of the DTT and 2 x 2-alpha-helix bundle protein adlayer were characterized by interfacial capacitance and impedance techniques. Reductive desorption was used to determine the coverage of the adlayers, giving values of 65 and 16 muC cm(-2) for DTT and 2 x 2-helix, respectively. The 2 x 2-alpha-helix bundle protein adlayers were imaged by in situ STM. The images indicated a dense monolayer according with the voltammetric data. No long-range order could be detected, but two clearly distinct STM contrasts were assigned to 2 x 2-alpha-helix bundle protein molecules oriented in parallel and antiparallel conformations. The template molecule DTT alone forms highly ordered 30-40 nm domains, giving an adlayer density which agreed well with the coverage determined by voltammetry. This could be exploited in STM imaging of mixed DTT/2 x 2-alpha-helix bundle protein monolayers, with clearly distinct STM patterns of the two components.