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Two-photon excited near-infrared fluorescence materials have garnered considerable attention because of their superior optical properties compared with other optical materials. Here, the authors use a convenient and efficient supramolecular approach to synthesize a two-photon excited near-infrared emissive co-crystalline material.

Thanks to its base stacking structure, DNA can behave as an electric wire, but external control of its electronic properties has not been achieved yet. Here, the authors show that DNA conductance can be switched electrochemically when a DNA base is replaced by the redox molecule anthraquinone.

Quantum interference effects offer opportunities to tune the electronic and thermoelectric response of a quantum-scale device over orders of magnitude. Here we focus on single-molecule devices, in which interference features may be strongly affected by both chemical and electronic modifications to the system. Although not always desirable, such a susceptibility offers insight into the importance of “small” terms, such as through-space coupling and many-body charge–charge correlations. Here we investigate the effect of these small terms using different Hamiltonian models with Hückel, gDFTB and many-body theory to calculate the transport through several single-molecule junctions, finding that terms that are generally thought to only slightly perturb the transport instead produce significant qualitative changes in the transport properties. In particular, we show that coupling of multiple interference features in cross-conjugated molecules by through-space coupling will lead to splitting of the features, as can correlation effects. The degeneracy of multiple interference features in cross-conjugated molecules appears to be significantly more sensitive to perturbations than those observed in equivalent cyclic systems and this needs to be considered if such supernodes are required for molecular thermoelectric devices.

The folding of a series of donor−acceptor oligorotaxanes is studied by means of molecular dynamics simulations. The oligorotaxanes consist of tetracationic cyclobis(paraquat-p-phenylene) rings threaded onto oligomers of 1,5-dioxynaphthalene linked by polyethers. Minimum energy structures are isolated using simulated annealing from which insights into the interactions responsible for the folding are extracted. The folding in vacuum is primarily driven by Coulombic interactions between the ionic species. In turn, in a high dielectric medium, the folding is the result of a series of conflicting interactions primarily orchestrated by the rings. In both cases, folded globular structures result. The observed secondary structures extend a previously proposed pleated π-stacked model for the folding that has been, in fact, observed in crystal samples of a [3]Rotaxane, the smallest of the oligorotaxanes considered. Simulations using two different force fields in the crystal environment, in vacuum, and in explicit solvent indicate that the π-stacked conformation adopted by the [3]Rotaxane is stable due to crystal packing effects rather than intracomplex interactions. The π-stacked conformation is also shown to be thermodynamically improbable in longer oligomers. [ABSTRACT FROM AUTHOR]

The effects of molecular conformation on conductance in oligosilane-bridged metal−molecule−metal junctions are studied theoretically using density functional theory combined with a nonequilibrium Green’s function approach. Varying the internal SiSiSiSi dihedral angles in hexasilane diamine chains changes the conductance by up to 3 orders of magnitude. This conformational dependence is due to the effects of σ-delocalization on the positions of the highest occupied molecular orbital (HOMO) energies. The conductance values for the different conformations are related to electron transfer rates in donor−bridge−acceptor systems, and the effect of shifting the injection energy is examined. The transport properties are found to be extremely sensitive to the alignment between the HOMO energies and Fermi level of the gold electrodes. [ABSTRACT FROM AUTHOR]

Raman scattering is a potentially important probe of structure, dynamics, and thermal properties of single-molecule conduction junctions. We combine a nonequilibrium Green’s function description of the junction with a generalized scattering theory of the Raman process, which provides the first theoretical description of Raman scattering from such systems. The voltage dependence of the Raman flux shows a characteristic behavior at the conductance threshold resulting from (a) partial populations in the ground and excited molecular levels that give rise to two scattering pathways as well as interference between them and (b) junction heating that affects the Raman intensities. Comparing “effective temperatures” obtained from Raman scattering and heat balance serves to establish the integrity of this concept for nonequilibrium junctions. [ABSTRACT FROM AUTHOR]

As an example of the use of inelastic transport to deduce structure in molecular transport junctions, we compute the orientation dependence of the Inelastic Electron Tunneling (IET) spectrum of the 1-pentane monothiolate. We find that upon increasing the tilting angle of the molecule with respect to the normal to the electrode the spectrum changes as the intensity of some vibrations is enhanced. These differences occur because for higher tilting angles the tunneling path that bypasses the terminal group grows in importance. IETS can therefore be used to establish the molecular orientation in junctions terminating with alkyl chains and to investigate experimentally the relative importance of the available tunneling paths. [ABSTRACT FROM AUTHOR]

A recently devised, discrete-dipole approximation (DDA) based method for computing optical forces is used to explore geometry dependent aspects of the light induced interactions between pairs of silver nanoparticles, including the influence of particle shape, relative positioning of the particles, and incident field orientation. The interactions are observed to have a large degree of generic character, independent of the details of the particle shape. The size of the optical forces is also compared to estimates for the van der Waals forces, and the results are used to assess the potential importance of radiation forces on recent experiments demonstrating photoinduced self-assembly of triangular silver nanoprisms. [ABSTRACT FROM AUTHOR]

We develop a series of propensity rules for interpreting inelastic electron tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared, and Raman spectra, because IETS features arise not from the field−dipole interaction characterizing these other spectroscopies but from vibronic modification of the electronic levels. Expansion of the Landauer−Imry formula in Taylor series in molecular normal coordinates gives a convenient, accurate perturbation-type formula for calculating both frequency and intensity of the IETS spectrum. Expansion in a Dyson-like form permits derivation of propensity rules, both symmetry-based and pathway-deduced, allowing correlation of structure and coupling geometry with the IETS spectrum. These propensity rules work very well for the calculated spectrum of five typical molecular bridges. [ABSTRACT FROM AUTHOR]

Processing digital signals on the molecular scale is of great interest. In this paper, we discuss the control of pulselike energy propagation through one-dimensional arrays of dipoles. Three systems are explored. In the first system, a chain of coaxial dipoles is gated by two control dipoles. Changing the orientation of these control dipoles lets us control the transfer of energy in the chain. In the other two systems, the chain−branch system and the two-branch system, two chains are used as an input and the propagation of energy is controlled by sending one or two signals toward the junction. Both systems can operate as a logical AND port. Their geometrical configurations are key to a well-defined control and operation of the AND port. [ABSTRACT FROM AUTHOR]

The article presents information on the synthesis and electrochemical characterization of a transition-metal-modified ligand-receptor. The energetics of weak interactions are difficult to quantify in biological ligand-receptor pairs. Insight into the biochemical role these forces play is critical to an understanding of signal transduction events and the drug discovery process. These weak interactions are essential in biological electron transfer events and are described in the semiclassical Marcus theory of donor-acceptor pairs. Modifying a native protein substrate to include a donor complex will permit an investigation of ligand-receptor binding events in solution where the acceptor is a redox mediator or an electrode. Ligands were used to synthesize electrochemically active transition metal complexes capable of binding avidin.