The intriguing role of L-cysteine in the modulation of chiroplasmonic properties of chiral gold nano-arrows.

Developing chiral plasmonic nanostructures represents a significant scientific challenge due to their multidisciplinary potential. Observations have revealed that the dichroic behavior of metal plasmons changes when chiral molecules are present in the system, offering promising applications in various fields such as nano-optics, asymmetric catalysis, polarization-sensitive photochemistry and molecular detection. In this study, we explored the synthesis of plasmonic gold nanoparticles and the role of cysteine in their chiroplasmonic properties.

Time-dependent quantum/continuum modeling of plasmon-enhanced electronic circular dichroism.

In this work, we present a multiscale real-time approach to study the plasmonic effects of a metal nanoparticle (NP) on the electronic circular-dichroism (ECD) spectrum of a chiral molecule interacting with it. The method is based on the time-evolution of the molecule's time-dependent wavefunction, expanded in the eigenstates of a perturbed Hamiltonian. A quantum description of the molecular system is coupled to a classical representation of the NP via a continuum model.

Combined experimental and computational study of the photoabsorption of the monodoped and nondoped nanoclusters AuPt(SR), AgPt(SR), and Ag(SR).

Assessing the accuracy of first-principles computational approaches is instrumental to predict electronic excitations in metal nanoclusters with quantitative confidence. Here we describe a validation study on the optical response of a set of monolayer-protected clusters (MPC). The photoabsorption spectra of Ag(DMBT), AgPt(DMBT) and AuPt(SCH), where DMBT is 2,4-dimethylbenzenethiolate and SCH is -butylthiolate, have been obtained at low temperature and compared with accurate TDDFT calculations.

Oxygen-Promoted on-Surface Synthesis of Polyboroxine Molecules.

We present a protocol for the on-surface synthesis of polyboroxine molecules derived from boroxine molecules precursors. This process is promoted by oxygen species present on the Au(111) surface: oxygen atoms facilitate the detachment of naphthalene units of trinaphthyl-boroxine molecules and bridge two unsaturated boroxine centers to form a boroxine-O-boroxine chemical motif. X-ray spectroscopic characterization shows that, as the synthesis process proceeds, it progressively tunes the electronic properties of the interface, thus providing a promising route to control the electron level alignment.

Dichroism of plasmonic chiral nanoalloys by rational design.

Time-dependent density functional theory (TDDFT) simulations are conducted on a series of chiral gold/silver alloy nanowires to explore whether silver doping can produce an enhancement of circular dichroism at the plasmon resonance in these systems, and to identify the quantum-mechanical origin of the observed effects. We find a strong plasmonic dichroism when one or two helixes of gold atoms are substituted by silver in a linear chiral nanotube, whose pure gold counterpart does not display any plasmonic dichroism, and we rationalize this finding in terms of "decoupling" the destructive interference of excitations in the pure gold nanotube via alloying. However, further attempts to increase the plasmonic dichroism by considering multi-shell gold nanowires in which one entire shell is doped with silver did not produce the desired effect, but rather a decrease in circular dichroism.

Unrevealing the Nitrogen Elusive Chirality of 3-Sulfanyl and 3-Sulfinyl N-Tosyl Isoindolinones by ECD Spectra: An Experimental and Theoretical Investigation.

The nitrogen-hybridization/pyramidalization of two solvated N-tosylisoindolinone derivatives having chiral residues in adjacent (I) or adjacent and distal (II) position has been investigated by a theoretical-computational procedure based on Molecular Dynamics simulations and Quantum-Chemical calculations. After validation of our methodology in providing a reliable repertory of conformations by modeling the electronic circular dichroism (EDC) spectra, the electronic features associated with N-pyramidalization were further characterized through Natural Bond Order (NBO) analysis. Comparing against the N-geometry observed in crystal structures as a reference, our findings reveal that the presence of neighbouring chiral centers induces a more pronounced N-pyramidalization in solution than in the solid state, both in I and II.

Peeking into the Femtosecond Hot-Carrier Dynamics Reveals Unexpected Mechanisms in Plasmonic Photocatalysis.

Plasmonic-driven photocatalysis may lead to reaction selectivity that cannot be otherwise achieved. A fundamental role is played by hot carriers, i.e.

Effects of Oxygen Adsorption on the Optical Properties of Ag Nanoparticles.

Plasmonic metal nanoparticles are efficient light harvesters with a myriad of sensing- and energy-related applications. For such applications, the optical properties of nanoparticles of metals such as Cu, Ag, and Au can be tuned by controlling the composition, particle size, and shape, but less is known about the effects of oxidation on the plasmon resonances. In this work, we elucidate the effects of O adsorption on the optical properties of Ag particles by evaluating the thermodynamic properties of O-decorated Ag particles with calculations based on the density functional theory and subsequently computing the photoabsorption spectra with a computationally efficient time-dependent density functional theory approach.

Electronic Structure of Pentagonal Carbon Nanocones: An ab Initio Study.

In this work, we investigate the electronic structure of a particular class of carbon nanocones having a pentagonal tip and symmetry. The ground-state nature of the wave function for these structures can be predicted by the recently proposed generalized Hückel rule that extends the original Hückel rule for annulenes to this class of carbon nanocones. In particular, the structures here considered can be classified as closed-shell or anionic/cationic closed-shells, depending on the geometric characteristics of the cone.

A Resolution of Identity Technique to Speed up TDDFT with Hybrid Functionals: Implementation and Application to the Magic Cluster Series Au(SCH) ( = 3-6).

The Resolution of Identity (RI) technique has been employed to speed up the use of hybrid exchange-correlation (xc) functionals at the TDDFT level using the Hybrid Diagonal Approximation. The RI has been implemented within the polTDDFT algorithm (a complex damped polarization method) in the AMS/ADF suite of programs. A speedup factor of 30 has been obtained with respect to a previous numerical implementation, albeit with the same level of accuracy.

Diverging conformations guide dipeptide self-assembly into crystals or hydrogels.

The prediction of dipeptide assembly into crystals or gels is challenging. This work reveals the diverging conformational landscape that guides self-organization towards different outcomes. and experimental data enabled deciphering of the electronic circular dichroism (ECD) spectra of self-assembling dipeptides to reveal folded or extended conformers as key players.

Time Evolution of Plasmonic Features in Pentagonal Ag Clusters.

In the present work, we apply recently developed real-time descriptors to study the time evolution of plasmonic features of pentagonal Ag clusters. The method is based on the propagation of the time-dependent Schrödinger equation within a singly excited TDDFT ansatz. We use transition contribution maps (TCMs) and induced density to characterize the optical longitudinal and transverse response of such clusters, when interacting with pulses resonant with the low-energy (around 2-3 eV, A1) size-dependent or the high-energy (around 4 eV, E1) size-independent peak.

What Contributes to the Measured Chiral Optical Response of the Glutathione-Protected Au Nanocluster?

The water-soluble glutathione-protected [Au(GSH)] nanocluster was investigated by integrating several methodologies such as molecular dynamics simulations, essential dynamics analysis, and state-of-the-art time-dependent density functional theory calculations. Fundamental aspects such as conformational, weak interactions and solvent effects, especially hydrogen-bonds, were included and found to play a fundamental role in assessing the optical response of this system. Our analysis demonstrated not only that the electronic circular dichroism is extremely sensitive to the solvent presence but also that the solvent itself plays an active role in the optical activity of such system, forming a chiral solvation shell around the cluster.

Electronic circular dichroism from real-time propagation in state space.

In this paper, we propose to compute the electronic circular dichroism (ECD) spectra of chiral molecules using a real-time propagation of the time-dependent Schrödinger equation (TDSE) in the space of electronic field-free eigenstates, by coupling TDSE with a given treatment of the electronic structure of the target. The time-dependent induced magnetic moment is used to compute the ECD spectrum from an explicit electric perturbation. The full matrix representing the transition magnetic moment in the space of electronic states is generated from that among pairs of molecular orbitals.

The Conformational Dynamics of the Ligands Determines the Electronic Circular Dichroism of the Chiral Au(SCHPh) Cluster.

Effects of the conformational dynamics of 2-PET protective ligands on the electronic circular dichroism (ECD) of the chiral Au(SCHPh) cluster are investigated. We adopt a computational protocol in which ECD spectra are calculated via the first principle polTDDFT approach on a series of conformations extracted from MD simulations by using Essential Dynamics (ED) analysis, and then properly weighted to predict the final spectrum. We find that the experimental spectral features are well reproduced, whereas significant discrepancies arise when the spectrum is calculated using the experimental X-ray structure.

Accurate Vertical Excitation Energies of BODIPY/Aza-BODIPY Derivatives from Excited-State Mean-Field Calculations.

We report a benchmark study of vertical excitation energies and oscillator strengths for the HOMO → LUMO transitions of 17 boron-dipyrromethene (BODIPY) structures, showing a large variety of ring sizes and substituents. Results obtained at the time-dependent density functional theory (TDDFT) and at the delta-self-consistent-field (ΔSCF) by using 13 different exchange correlation kernels (within LDA, GGA, hybrid, and range-separated approximations) are benchmarked against the experimental excitation energies when available. It is found that the time-independent ΔSCF DFT method, when used in combination with hybrid PBE0 and B3LYP functionals, largely outperforms TDDFT and can be quite competitive, in terms of accuracy, with computationally more costly wave function based methods such as CC2 and CASPT2.

Probing Intermolecular H-Bonding Interactions in Cyanuric Acid Networks: Quenching of the N -Edge Sigma Resonances.

The electronic characterization of the cyanuric acid both in gas phase and when embedded within an H-bonded scheme forming a monolayer on the Au(111) surface has been performed by means of X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The experimental spectra at the N, O, and C -edges have been assigned with the support of DFT calculations, and the combination between theory and experiment has allowed to us investigate the effect of the H-bonding intermolecular interaction on the spectra. In particular, the H-bond formation in the monolayer leads to a quenching of the N 1s NEXAFS resonances associated with transitions to the sigma empty orbitals localized on the N-H portion of the imide group.

A computational approach for modeling electronic circular dichroism of solvated chromophores.

The present study consists in a novel computational protocol to model the UV-circular dichroism spectra of solvated species. It makes use of quantum-chemical calculations on a series of conformations of a flexible chromophore or on a series of chromophore/solvent clusters extracted from molecular dynamic simulations. The protocol is described and applied to the aqueous cationic tripeptide GAG and to the aqueous neutral decapeptide (GVGVP) .

Optimization of density fitting auxiliary Slater-type basis functions for time-dependent density functional theory.

A new set of auxiliary basis function suitable to fit the induced electron density is presented. Such set has been optimized in order to furnish accurate absorption spectra using the complex polarizability algorithm of time-dependent density functional theory (TDDFT). An automatic procedure has been set up, able, thanks to the definition of suitable descriptors, to evaluate the resemblance of the auxiliary basis-dependent calculated spectra with respect to a reference.

Coupling between Plasmonic and Molecular Excitations: TDDFT Investigation of an Ag-Nanorod/BODIPY-Dye Interaction.

A time-dependent density functional theory (TDDFT) computational approach is employed to study the optical coupling between a plasmonic system (a Ag nanorod) and a fluorescent dye (BODIPY). It is found that the BODIPY dye can interact with a plasmonic system in a rather different and selective way according to the mutual orientation of the fragments. Indeed, (i) the plasmon excitation turns out to be sensitive to the presence of the BODIPY transition and (ii) this can lead to amplify or suppress the resonance accordingly to the relative orientation of the corresponding transition dipoles.

Computational NEXAFS Characterization of Molecular Model Systems for 2D Boroxine Frameworks.

The electronic properties of 2D boroxine networks are computationally investigated by simulating the NEXAFS spectra of a series of molecular models, with or without morphologic defects, with respect to the ideal honeycomb structure. The models represent portions of an irregular 2D boroxine framework obtained experimentally, as supported by the Au(111) surface. The B K-edge NEXAFS spectra are calculated within the transition potential (TP) approximation (DFT-TP).

Continuum Electronic States: The Tiresia Code.

A multicenter (LCAO) B-spline basis is described in detail, and its capabilities concerning affording convergent solutions for electronic continuum states and wavepacket propagation are presented. It forms the core of the Tiresia code, which implements static-DFT and TDDFT hamiltonians, as well as single channel Dyson-DFT and Dyson-TDDFT descriptions to include correlation in the bound states. Together they afford accurate and computationally efficient descriptions of photoionization properties of complex systems, both in the single photon and strong field environments.

Plasmonic Circular Dichroism in Chiral Gold Nanowire Dimers.

We report a computational study at the time-dependent density functional theory (TDDFT) level of the chiro-optical spectra of chiral gold nanowires coupled in dimers. Our goal is to explore whether it is possible to overcome destructive interference in single nanowires that damp chiral response in these systems and to achieve intense plasmonic circular dichroism (CD) through a coupling between the nanostructures. We predict a huge enhancement of circular dichroism at the plasmon resonance when two chiral nanowires are intimately coupled in an achiral relative arrangement.