Improved Scaling of Molecular Network Calculations: The Emergence of Molecular Domains.

The design of materials needed for the storage, delivery, and conversion of (re)useable energy is still hindered by the lack of new, hierarchical molecular screening methodologies that encode information on more than one length scale. Using a molecular network theory as a foundation, we show that to describe charge transport in disordered materials the network methodology must be scaled-up. We detail the scale-up through the use of adjacency lists and depth first search algorithms for during operations on the adjacency matrix.

Ultrahigh-Vacuum Tip-Enhanced Raman Spectroscopy.

Molecule-surface interactions and processes are at the heart of many technologies, including heterogeneous catalysis, organic photovoltaics, and nanoelectronics, yet they are rarely well understood at the molecular level. Given the inhomogeneous nature of surfaces, molecular properties often vary among individual surface sites, information that is lost in ensemble-averaged techniques. In order to access such site-resolved behavior, a technique must possess lateral resolution comparable to the size of surface sites under study, analytical power capable of examining chemical properties, and single-molecule sensitivity.

Molecular Dynamics Simulation and Experimental Studies of Gold Nanoparticle Templated HDL-like Nanoparticles for Cholesterol Metabolism Therapeutics.

High-density lipoprotein (HDL) plays an important role in the transport and metabolism of cholesterol. Mimics of HDL are being explored as potentially powerful therapeutic agents for removing excess cholesterol from arterial plaques. Gold nanoparticles (AuNPs) functionalized with apolipoprotein A-I and with the lipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[3-(2-pyridyldithio)propionate] have been demonstrated to be robust acceptors of cellular cholesterol.

Direct Observation of a Charge-Transfer State Preceding High-Yield Singlet Fission in Terrylenediimide Thin Films.

Singlet exciton fission (SF) in organic chromophore assemblies results in the conversion of one singlet exciton (S) into two triplet excitons (T), provided that the overall process is exoergic, i.e., E(S) > 2E(T).

Implementation of INDO/SCI with COSMO Implicit Solvation and Benchmarking for Solvatochromic Shifts.

Accurate and rapid quantum mechanical prediction of solvatochromic shifts, particularly in systems where charge transfer plays a significant role, is important for many aspects of molecular and material design. Although the semiempirical INDO/SCI approach is computationally efficient and performs well for charge-transfer states, the availability of implicit solvent approaches has been limited. Here, we implement the COSMO solvent model with a perturbative state-specific correction to the excited-state energies with the INDO/SCI method.

Aluminum Film-Over-Nanosphere Substrates for Deep-UV Surface-Enhanced Resonance Raman Spectroscopy.

We report here the first fabrication of aluminum film-over nanosphere (AlFON) substrates for UV surface-enhanced resonance Raman scattering (UVSERRS) at the deepest UV wavelength used to date (λ = 229 nm). We characterize the AlFONs fabricated with two different support microsphere sizes using localized surface plasmon resonance spectroscopy, electron microscopy, SERRS of adenine, tris(bipyridine)ruthenium(II), and trans-1,2-bis(4-pyridyl)-ethylene, SERS of 6-mercapto-1-hexanol (as a nonresonant molecule), and dielectric function analysis. We find that AlFONs fabricated with the 210 nm microspheres generate an enhancement factor of approximately 10, which combined with resonance enhancement of the adsorbates provides enhancement factors greater than 10.

Tip-Enhanced Raman Voltammetry: Coverage Dependence and Quantitative Modeling.

Electrochemical atomic force microscopy tip-enhanced Raman spectroscopy (EC-AFM-TERS) was employed for the first time to observe nanoscale spatial variations in the formal potential, E, of a surface-bound redox couple. TERS cyclic voltammograms (TERS CVs) of single Nile Blue (NB) molecules were acquired at different locations spaced 5-10 nm apart on an indium tin oxide (ITO) electrode. Analysis of TERS CVs at different coverages was used to verify the observation of single-molecule electrochemistry.

Energetic and Dynamic Analysis of Transport of Na and K through a Cyclic Peptide Nanotube in Water and in Lipid Bilayers.

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na and K are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(d-Leu-Trp)-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and in lipid bilayers, and that the selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel and the coupling of the ion motions with the chain-structured water movements inside the channel lead to a decrease of the diffusion coefficients far away from the channel entrance and also reduced coefficients inside the channel.

Magneto-Optical Response of Cobalt Interacting with Plasmonic Nanoparticle Superlattices.

The magneto-optical Kerr effect is a striking phenomenon whereby the optical properties of a material change under an applied magnetic field. Though promising for sensing and data storage technology, these properties are typically weak in magnitude and are inherently limited by the bulk properties of the active magnetic material. In this work, we theoretically demonstrate that plasmonic thin-film assemblies on a cobalt substrate can achieve tunable transverse magneto-optical (TMOKE) responses throughout the visible and near-infrared (300-900 nm).

Programmable and reversible plasmon mode engineering.

Plasmonic nanostructures with enhanced localized optical fields as well as narrow linewidths have driven advances in numerous applications. However, the active engineering of ultranarrow resonances across the visible regime-and within a single system-has not yet been demonstrated. This paper describes how aluminum nanoparticle arrays embedded in an elastomeric slab may exhibit high-quality resonances with linewidths as narrow as 3 nm at wavelengths not accessible by conventional plasmonic materials.

Enabling singlet fission by controlling intramolecular charge transfer in π-stacked covalent terrylenediimide dimers.

When an assembly of two or more molecules absorbs a photon to form a singlet exciton, and the energetics and intermolecular interactions are favourable, the singlet exciton can rapidly and spontaneously produce two triplet excitons by singlet fission. To understand this process is important because it may prove to be technologically significant for enhancing solar-cell performance. Theory strongly suggests that charge-transfer states are involved in singlet fission, but their role has remained an intriguing puzzle and, up until now, no molecular system has provided clear evidence for such a state.

Correction: In solution SERS sensing using mesoporous silica-coated gold nanorods.

Correction for 'In solution SERS sensing using mesoporous silica-coated gold nanorods' by Zhe Gao, et al., Analyst, 2016, 141, 5088-5095.

Understanding the vibrational mode-specific polarization effects in femtosecond Raman-induced Kerr-effect spectroscopy.

Optically heterodyne-detected femtosecond Raman-induced Kerr-effect spectroscopy (OHD-FRIKES) was observed in neat cyclohexane. In this Letter, an examination of the effect of the Raman pump ellipticity on the multiplex OHD-FRIKES spectra is discussed. The Raman pump ellipticity scanned OHD-FRIKES results reproduce anomalous observables from previous OHD-FRIKES experiments and suggest new methods of tracking transient vibrational mode polarization in complex systems.

Electronic Structure and Potential Reactivity of Silaaromatic Molecules.

Silicon-based materials are crucial for conventional electronics. The fascinating properties of the new two-dimensional material silicene, the silicon analogue of graphene (one atom-thick silicon sheets), offer a potential bridge between conventional and molecular electronics. The ground-state configuration of silicene is buckled, which compromises optimal constructive overlap of p orbitals.

Supramolecular Double-Helix Formation by Diastereoisomeric Conformations of Configurationally Enantiomeric Macrocycles.

Solid-state superstructures, resulting from assemblies programmed by homochirality, are attracting considerable attention. In addition, artificial double-helical architectures are being investigated, especially in relation to the ways in which homochiral small molecules can be induced to yield helical forms as a result of chiral induction. Herein, we report the highly specific self-assembly upon crystallization of a double-helical superstructure from an enantiopure macrocyclic dimer which adopts two diastereoisomeric conformations in a molar ratio of 1.

Surface-Enhanced Femtosecond Stimulated Raman Spectroscopy at 1 MHz Repetition Rates.

Surface-enhanced femtosecond stimulated Raman spectroscopy (SE-FSRS) is an ultrafast Raman technique that combines the sensitivity of surface-enhanced Raman scattering with the temporal resolution of femtosecond stimulated Raman spectroscopy (FSRS). Here, we present the first successful implementation of SE-FSRS using a 1 MHz amplified femtosecond laser system. We compare SE-FSRS and FSRS spectra measured at 1 MHz and 100 kHz using both equal pump average powers and equal pump energies to demonstrate that higher repetition rates allow spectra with higher signal-to-noise ratios to be obtained at lower pulse energies, a significant advance in the implementation of SE-FSRS.

Quantum Mechanical Identification of Quadrupolar Plasmonic Excited States in Silver Nanorods.

Quadrupolar plasmonic modes in noble metal nanoparticles have gained interest in recent years for various sensing applications. Although quantum mechanical studies have shown that dipolar plasmons can be modeled in terms of excited states where several to many excitations contribute coherently to the transition dipole moment, new approaches are needed to identify the quadrupolar plasmonic states. We show that quadrupolar states in Ag nanorods can be identified using the semiempirical INDO/SCI approach by examining the quadrupole moment of the transition density.

Reversible Shape and Plasmon Tuning in Hollow AgAu Nanorods.

The internal structure of hollow AgAu nanorods created by partial galvanic replacement was manipulated reversibly, and its effect on optical properties was mapped with nanometer resolution. Using the electron beam in a scanning transmission electron microscope to create solvated electrons and reactive radicals in an encapsulated solution-filled cavity in the nanorods, Ag ions were reduced nearby the electron beam, reshaping the core of the nanoparticles without affecting the external shape. The changes in plasmon-induced near-field properties were then mapped with electron energy-loss spectroscopy without disturbing the internal structure, and the results are supported by finite-difference time-domain calculations.

Bisboronic Acids for Selective, Physiologically Relevant Direct Glucose Sensing with Surface-Enhanced Raman Spectroscopy.

This paper demonstrates the direct sensing of glucose at physiologically relevant concentrations with surface-enhanced Raman spectroscopy (SERS) on gold film-over-nanosphere (AuFON) substrates functionalized with bisboronic acid receptors. The combination of selectivity in the bisboronic acid receptor and spectral resolution in the SERS data allow the sensors to resolve glucose in high backgrounds of fructose and, in combination with multivariate statistical analysis, detect glucose accurately in the 1-10 mM range. Computational modeling supports assignments of the normal modes and vibrational frequencies for the monoboronic acid base of our bisboronic acids, glucose and fructose.