Photoswitchable architecture transformation of a DNA-hybrid assembly at the microscopic and macroscopic scale

Molecular recognition-driven self-assembly employing single-stranded DNA (ssDNA) as a template is a promising approach to access complex architectures from simple building blocks. Oligonucleotide-based nanotechnology and soft-materials benefit from the high information storage density, self-correction, and memory function of DNA. Here we control these beneficial properties with light in a photoresponsive biohybrid hydrogel, adding an extra level of function to the system. An ssDNA template was combined with a complementary photo-responsive unit to reversibly switch between various functional states of the supramolecular assembly using a combination of light and heat. We studied the structural response of the hydrogel at both the microscopic and macroscopic scale using a combination of UV-vis absorption and CD spectroscopy, as well as fluorescence, transmission electron, and atomic force microscopy. The hydrogels grown from these supramolecular self-assembly systems show remarkable shape-memory properties and imprinting shape-behavior while the macroscopic shape of the materials obtained can be further manipulated by irradiation.

Molecular recognition-driven self-assembly employing single-stranded DNA (ssDNA) as a template is a promising approach to access complex architectures from simple building blocks.

Doublet-Singlet-Doublet Transition in a Single Organic Molecule Magnet On-Surface Constructed with up to 3 Aluminum Atoms

Starting from a long aza-starphene neutral and nonmagnetic organic molecule, a single-molecule magnet is on-surface constructed using up to 3 light nonmagnetic aluminum (Al) atoms. Seldom observed in solution with transition-metal atoms and going from 1 to 3 Al coordinated atoms, the doublet-singlet-doublet transition is easily on-surface accessible using the scanning tunneling microscope single-atom and single-molecule manipulations on a gold(111) surface. With 3 coordinated Al atoms, the lateral vibration modes of the Al3-aza-starphene molecule magnet are largely frozen. Using the Kondo states, this opens the observation of the in-phase Al vertical atom vibrations and out-of-phase central phenyl vibrations.

A Single-Molecule Digital Full Adder

A specifically designed aza-starphene molecule is presented where contacting one, two, and/or three single Al adatoms allows this molecule to function as a "3-inputs & 2-outputs" digital full adder on a Au(111) surface. Sequentially positioning single Al adatoms with atomic precision to interact with aza-starphene, inputs one classical digit per Al, which is converted to quantum information by the molecule. The intramolecular logical calculations do not require a solid-state digital full adder cascade-like architecture. The measured Boolean truth table results in part from the quantum level repulsion effect and in part from a nonlinear magnetic effect also intrinsic to the aza-starphene molecule with its contacted Al adatoms.

Synthesis of a Crushed Fullerene C60H24 through Sixfold Palladium-Catalyzed Arylation

The synthesis of a new C3v -symmetric crushed fullerene C60H24 (5) has been accomplished in three steps from truxene through sixfold palladium-catalyzed intramolecular arylation of a syn-trialkylated truxene precursor. Laser irradiation of 5 induces cyclodehydrogenation processes that result in the formation of C60, as detected by LDI-MS.

Contacting a conjugated molecule with a surface dangling bond dimer on a hydrogenated Ge(001) surface allows imaging of the hidden ground electronic state

Fabrication of single-molecule logic devices requires controlled manipulation of molecular states with atomic-scale precision. Tuning molecule-substrate coupling is achieved here by the reversible attachment of a prototypical planar conjugated organic molecule to dangling bonds on the surface of a hydrogenated semiconductor. We show that the ground electronic state resonance of a Y-shaped polyaromatic molecule physisorbed on a defect-free area of a fully hydrogenated surface cannot be observed by scanning tunneling microscopy (STM) measurements because it is decoupled from the Ge bulk states by the hydrogen-passivated surface. The state can be accessed by STM only if the molecule is contacted with the substrate by a dangling bond dimer. The reversibility of the attachment processes will be advantageous in the construction of surface atomic-scale circuits composed of single-molecule devices interconnected by the surface dangling bond wires.

Synthesis of fluoranthenes by hydroarylation of alkynes catalyzed by gold(I) or gallium trichloride

Electrophilic gold(I) catalyst 6 competes with GaCl₃ as the catalyst of choice in the synthesis of fluoranthenes by intramolecular hydroarylation of alkynes. The potential of this catalyst for the preparation of polyarenes is illustrated by a synthesis of two functionalized decacyclenes in a one-pot transformation in which three C–C bonds are formed with high efficiency.

Organic molecules reconstruct nanostructures on ionic surfaces

Modification and functionalization of the atomic-scale structure of insulating surfaces is fundamental to catalysis, self-assembly, and single-molecule technologies. Specially designed syn-5,10,15-tris(4-cyanophenylmethyl)truxene molecules can reshape features on an ionic KBr (001) surface. Atomic force microscopy images demonstrate that both KBr monolayer islands and pits can reshape from rectangular to round structures, a process which is directly facilitated by molecular adsorption. Simulations reveal that the mechanism of the surface reconstruction consists of collective atomic hops of ions on the step edges of the islands and pits, which correlate with molecular motion. The energy barriers for individual processes are reduced by the presence of the adsorbed molecules, which cause surface structural changes. These results show how appropriately designed organic molecules can modify surface morphology on insulating surfaces. Such strongly adsorbed molecules can also serve as anchoring sites for building new nanostructures on inert insulating surfaces.

Manipulating molecular quantum states with classical metal atom inputs: demonstration of a single molecule NOR logic gate

Quantum states of a trinaphthylene molecule were manipulated by putting its naphthyl branches in contact with single Au atoms. One Au atom carries 1-bit of classical information input that is converted into quantum information throughout the molecule. The Au-trinaphthylene electronic interactions give rise to measurable energy shifts of the molecular electronic states demonstrating a NOR logic gate functionality. The NOR truth table of the single molecule logic gate was characterized by means of scanning tunnelling spectroscopy.

Functionalized truxenes: adsorption and diffusion of single molecules on the KBr(001) surface

In this work, we have studied the adsorption and diffusion of large functionalized organic molecules on an insulating ionic surface at room temperature using a noncontact atomic force microscope (NC-AFM) and theoretical modeling. Custom designed syn-5,10,15-tris(4-cyanophenylmethyl)truxene molecules are adsorbed onto the nanoscale structured KBr(001) surface at low coverages and imaged with atomic and molecular resolution with the NC-AFM. The molecules are observed rapidly diffusing along the perfect monolayer step edges and immobilized at monolayer kink sites. Extensive atomistic simulations elucidate the mechanisms of adsorption and diffusion of the molecule on the different surface features. The results of this study suggest methods of controlling the diffusion of adsorbates on insulating and nanostructured surfaces.

Synthesis of arenes and heteroarenes by hydroarylation reactions catalyzed by electrophilic metal complexes

The hydroarylation of alkynes (also known as arylation of alkynes or alkenylation of arenes) catalyzed by gold or other electrophilic metal salts or complexes is reviewed from synthetic and mechanistic perspectives.

Proton-abstraction mechanism in the palladium-catalyzed intramolecular arylation: substituent effects

The regioselectivity observed in the intramolecular palladium-catalyzed arylation of substituted bromobenzyldiarylmethanes as well as theoretical results demonstrate that the Pd-catalyzed arylation proceeds by a mechanism involving a proton abstraction by the carbonate, or a related basic ligand. The reaction is facilitated by electron-withdrawing substituents on the aromatic ring, which is inconsistent with an electrophilic aromatic-substitution mechanism. The more important directing effect is exerted by electron-withdrawing substituents ortho to the reacting site.

Palladium catalyzed arylation for the synthesis of polyarenes

We present the current understanding on the mechanism of palladium-catalyzed arylation, which involves a proton abstraction by the base. In addition, we present selected examples of the application of this reaction for the synthesis of large polyarenes to highlight the variety of catalysts and reaction conditions that are currently used.