RESUMEN

Nanostructures, fabricated by locating molecular building blocks in well-defined positions, for example, on a lattice, are ideal platforms for studying atomic-scale quantum effects. In this context, STM data obtained from self-assembled Bis(phthalocyaninato) Terbium (III) (TbPc2) single-molecule magnets on various substrates have raised questions about the conformation of the TbPc2 molecules within the lattice. In order to address this issue, molecular dynamics simulations were carried out on a 2D assembly of TbPc2 molecules. The calculations are in excellent agreement with the experiment, and thus improve our understanding of the self-assembly process. In particular, the calculated electron density of the molecular assembly compares well with STM contrast of self-assembled TbPc2 on Au(111), simultaneously providing the conformation of the two Pc ligands of the individual double-decker molecule. This approach proves valuable in the identification of the STM contrast of LnPc2 layers and could be used in similar cases where it is difficult to interpret the STM images of an assembly of molecular complexes.

RESUMEN

The facile syntheses of enantiomeric atomically precise silver clusters starting from achiral ligands remain a substantial challenge to explore. In this work, a pair of atomically precise enantiomers of R/S-[Ag17Cl(iPrS)9S(CH3COO)5H2O] (R/S-Ag17, iPrS = isopropanethiolate) clusters have been synthesized using a viable solvothermal approach. The chirality of the resulting enantiomeric R/S-Ag17 clusters is attributed to the asymmetric arrangement of surface achiral ligands. Both R/S-Ag17 enantiomers could form the two-dimensional (2D) assemblies via intercluster interactions of basic building blocks containing Ag16S8 moieties, iPrS-Ag motifs, and S2- linkers. Such a small ligand-induced 2D assembly greatly contributes to the enhancement of thermal stability and photocatalytic activity of R/S-Ag17 clusters, providing possibilities for exploring robust coinage cluster-based assembly with attractive catalytic properties.

RESUMEN

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion-enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two-dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C-H⋅⋅⋅π bonding.

RESUMEN

2D polymer sheets containing azobenzene are successfully prepared by a facile strategy of "2D self-assembly polymerization (2DSP)" via free radical polymerization in solution. A bola amphiphile containing azobenzene as a novel monomer is designed and synthesized. The results indicate that single-layer covalent pseudo-2D polymers on a micrometer scale are obtained after polymerization with vinyl monomers. Moreover, the 2D polymer sheets are highly sensitive to UV light due to incorporation of azobenzene groups into the polymer. Upon alternative irradiation with UV and visible light, the morphological transformation between sheets and rolled-up nanotubes can be achieved based on the reversible trans-to-cis photoisomerization of azobenzene units in the 2D polymer sheets.

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RESUMEN

Electron-rich (donor) and electron-deficient (acceptor) units to construct donor-acceptor (D-A) conjugated macrocycles were investigated to elucidate their interactions with electron-deficient fullerene. Triphenylamine and 4,7-bisthienyl-2,1,3-benzothiadiazole were alternately linked through acetylene, as the donor and acceptor units, respectively, for pentagonal 3B2A and hexagonal 4B2A macrocycles. As detected by scanning tunneling microscopy, both D-A macrocycles were found to form an interesting concentration-controlled nanoporous monolayer on highly oriented pyrolytic graphite, which could effectively capture fullerene. Significantly, the fullerene filling was cavity-size-dependent with only one C70 or PC71BM molecule accommodated by 3B2A, while two were accommodated by 4B2A. Density functional theory calculations were also utilized to gain insight into the host-guest systems and indicted that the S···π contact is responsible for stabilizing these host-guest systems. Owing to the ellipsoidal shape of C70, C70 molecules are standing or lying in molecular cavities depending on the energy optimization. For the 3B2A/PC71BM blended film, PC71BM was intercalated into the cavity formed by the macrocycle 3B2A and provided excellent power conversion efficiency despite the broad band gap (2.1 eV) of 3B2A. This study of D-A macrocycles incorporating fullerene provides insights into the interaction mechanism and electronic structure in the host-guest complexes. More importantly, this is a representative example using D-A macrocycles as a donor to match with the spherical fullerene acceptor for photovoltaic applications, which offer a good approach to achieve molecular scale p-n junctions for substantially enhanced efficiencies of organic solar cells through replacing linear polymer donors by cyclic conjugated oligomers.

RESUMEN

Adsorption of sequential amphiphilic peptides on solid substrates triggered the spontaneous construction of nanoscaled architecture. An amphiphilic peptide designed with a cationic amino acid as a hydrophilic residue turned an anionic mica substrate into a water-repellent surface, simply by adsorbing it on the substrate surface. In contrast, an amphiphilic peptide designed with an anionic amino-acid residue formed a precisely controlled fiber array comprising a ß-sheet fiber monolayer at the anionic substrate/water interface. This phenomenon was based on the secondary structural transition from random-coil to ß-sheet, which occurred specifically when amphiphilic peptide adsorbed on the substrate surface. Such surface-specific nonorder/order transition was implemented by exploiting the strength of adsorption between the peptide and the substrate. A strategic design exploiting weak bonding such as hydrophobic interactions is essential for constructing precisely controlled nano-architectures in two dimensions.

RESUMEN

An amphiphilic peptide derivative, conjugated to polyethylene glycol (PEG) via the C-terminus, spontaneously assembled into nanodot and nanofiber arrays aligned with nanometer periodicity at the solid/water interface. The obtained planar structure was precisely controlled by the ß-sheet conformation of the peptide on the surface, while the peptide segment adopted a random-coil in aqueous solution. The peptide and PEG segments were hierarchically segregated after the peptide-PEG conjugate was adsorbed on the substrate, and the peptide segment transitioned from a random-coil to a ß-sheet conformation specifically at the solid/water interface. In this 2D self-assembly, the high dispersity of the peptide-PEG molecule in solution such that it exists as single molecules is essential for improving the uniformity of the 2D patterned nanostructures. The secondary structure based on the peptide segment was controlled by pH of the solution. Configuration of the peptide-PEG conjugate was also controlled by the temperature of the solution, which depended on the lower critical solution temperature (LCST) of the PEG segments. The variation in concentration of the peptide-PEG conjugate drastically influenced the morphologies of the 2D nanostructures because of the difference in the adsorbed amounts at equilibrium.

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