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New materials for transparent luminescent solar concentrators (TLSCs) are of large interest. Therefore, we investigated the optical properties of J-aggregates-like oligomers (hereinafter referred to as J-aggregates) based on covalently bound squaraine dyes in toluene solvent using DFT and TD-DFT methods. In addition, the rate constants needed for the prediction of fluorescence quantum yield (QY) have been calculated using Fermi's Golden rule and vertical harmonic approximation (VH) for ground and excited states. In the context of QY prediction, different broadening of the lineshape has also been employed. We found that J-aggregates based on squaraine dyes exhibit near-infrared (NIR) selective absorption and emission as well as high fluorescence QY. Comparison of the properties obtained for dimers, trimers and tetramers belonging to two classes (SQA and SQB) of J-aggregates allows us to select the tetramer of SQA J-aggregates as suitable for application. The scaling model for N ≥ 4 monomer subunits supports quantitative findings. Therefore, we propose J-aggregates containing N ≥ 4 subunits of SQA with a central squaric acid ring with two oxygen atoms in toluene solvent as a suitable candidate for TLSC application.

Theoretical study of structural, optical, and photovoltaic properties of novel bio-nano hybrids (dye-nanocluster), as well as at TiO 2 surface model support is presented in the context of the application for dye-sensitized solar cells (DSSC). A group of anthocyanidin dyes (pelargonidin, cyanidin, delphinidin, peonidin, petunidin, and malvidin) represented by cyanidin covalently bound to silver nanoclusters (NCs) with even or odd number of valence electrons have been investigated using DFT and TDDFT approach. The key role of nanoclusters as acceptors in hybrids cyanidin-NC has been shown. The nanoclusters with an even number of valence electrons are suitable as acceptors in hybrids. The interaction of bio-nano (cyanidin-NC) hybrid with the TiO 2 surface model has been investigated in the context of absorption in near-infrared (NIR) and charge separation due to donor and acceptor subunits. Altogether, the theoretical concept serves to identify the key steps in the design of novel solar cells based on bio-nano hybrids at TiO 2 surface for DSSC application., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Gold nanoclusters (Au NCs) are an emerging class of luminescent nanomaterials but still suffer from moderate photoluminescence quantum yields. Recent efforts have focused on tailoring their emission properties. Introducing zwitterionic ligands to cap the metallic kernel is an efficient approach to enhance their one-photon excitation fluorescence intensity. In this work, we extend this concept to the nonlinear optical regime, i.e., two-photon excitation fluorescence. For a proper comparison between theory and experiment, both ligand and solvent effects should be considered. The effects of ligand shell size and of aqueous solvent on the optical properties of zwitterion functionalized gold nanoclusters have been studied by performing quantum mechanics/molecular mechanics (QM/MM) simulations.

The ability of gold(i) thiolates to self-assemble into supramolecular architectures opens the route for a new class of nanomaterials with a unique structure-optical property relationship. However, for a confirmed structure-optical property relationship, a control of the supramolecular architectures is required. In this work, we report a simple synthesis of sub-100 nanometer gold-cysteine and silver doped gold-cysteine supramolecular assemblies. We explore in particular silver-doping as a strategy to enhance the optical properties of these supramolecular assemblies. By an accurate characterization of as-synthesized supramolecular nanoparticles, we have been able to measure for the first time, their absolute two-photon absorption cross-section, two-photon excited fluorescence cross-section and first hyperpolarizabilities at different near-IR wavelengths. Huge values are obtained for silver doped gold-cysteine supramolecular assemblies, as compared to their corresponding undoped counterpart. In addition, we employ DFT and TD-DFT methods to study the geometric and electronic structures of model gold-cysteine and silver doped gold-cysteine compounds in order to address the structure-linear/nonlinear optical property relationship. The aim is to gain insights into the origin of the nonlinear optical enhancement of silver-doped gold supramolecular assemblies.

We report theoretical and experimental results on two-photon absorption (TPA) cross section of thiolated small silver cluster Ag15L11 exhibiting extraordinary large TPA in red. Our findings provide the responsible mechanism and allow proposing new classes of nanoclusters with large TPAs which are promising for biological and medical applications.

The bis(diphenylphosphino)methane (L = Ph2PCH2PPh2) ligated silver deuteride nanocluster dication, [Ag10D8L6](2+), has been synthesised in the condensed phase via the reaction of bis(diphenylphosphino)methane, silver nitrate and sodium borodeuteride in the methanol : chloroform (1 : 1) mixed solvent system. The photoionisation and photofragmentation of this mass-selected cluster were studied using a linear ion trap coupled to the DESIRS VUV beamline of the SOLEIL Synchrotron. At 15.5 eV the main ionic products observed are [Ag10D8L5](2+), [Ag10D8L4](2+), [Ag10D8L6](3+)˙, [Ag9D8L4](2+)˙, and [AgL2](+). The later two products arise from fragmentation of [Ag10D8L6](3+)˙. An analysis of the yields of these product ions as a function of the photon energy reveals the onset for the formation of [AgL2](+) and [Ag9D8L4](2+)˙ is around 2 eV higher than that for ionisation to produce [Ag10D8L5](3+)˙. The onset of ionisation energy of [Ag10D8L6](2+) was determined to be 9.3 ± 0.3 eV from a fit of the yield of the product ion, [Ag10D8L6](3+)˙, as a function of the VUV photon energy. DFT calculations at the RI-PBE/RECP-def2-SVP level of theory were carried out to search for a possible structure of the cluster and to estimate its vertical and adiabatic ionisation energies. The calculated lowest energy structure of the [Ag10D8L6](2+) nanocluster contains a symmetrical bicapped square antiprism as a silver core in which hydrides are located as a mix of triangular faces and edges. Four of the bisphosphines bind to the edges of the cluster core as bidentate ligands, the remaining two bisphosphines bind via a single phosphorus donor atom to each of the apical silver atoms. The DFT calculated adiabatic ionisation energy for this structure is 8.54 eV, in satisfactory agreement with experiment.

The reactions of ruthenium clusters, Rux(+) (x = 2-5), and ruthenium oxide clusters, RuxOy(+) (x = 2-5, y = 1-2), with water molecules have been investigated by gas phase ion trap mass spectrometry and first principle density functional calculations. The joint experimental and theoretical study reveals that the reactions of the ruthenium oxide clusters with water are considerably more efficient. This is assigned theoretically to the stronger binding of the water molecules to RuxOy(+) and, more importantly, to water activation leading to an efficient hydrogen transfer reaction from the water molecules to the oxygen atoms of the ruthenium oxide clusters. The theoretically predicted hydrogen shift reaction has been confirmed experimentally through (16)O/(18)O isotope exchange experiments. Calculated energy profiles for the reactions of selected oxide clusters with water illustrate that the oxygen isotope exchange relies on the facile transfer of hydrogen atoms via [1,3] shift reactions between the oxygen atoms of the complexes due to the relatively low barriers involved. These findings might open perspectives for the future realization of water oxidation driven by ruthenium oxide clusters.

We present a joint theoretical and experimental study of the structure selective optical properties of cationic and anionic histidine-silver complexes with Ag and Ag3 which were prepared in the gas phase using mass spectroscopy coupled to electrospray ion source. Our TDDFT calculations provide general insight into the nature of electronic excitations at the metal-bioorganic interface that involve π-π* excitation within bioorganic subunits, charge transfer between two subunits and intrametallic excitations. The binding of silver to histidine, one of the most important amino acids, induces red shift in the optical absorption of protonated histidine particularly for anionic species. The presence of the smallest metallic subunit Ag3 increases the intensity of low energy transitions of histidine illustrating a metal cluster-induced enhancement of absorption of biomolecules in hybrid systems. Comparison of calculated absorption spectra with experimental photofragmentation yield provides structural assignment of the measured spectroscopic patterns. Our findings may serve to establish silver-labeling as the tool for the detection of histidine or histidine-tagged proteins.

Gas phase reactivity observed in an ion trap was used to produce silver clusters protected with thioglycolic acid. Fragmentation pathways as well as optical properties were explored experimentally and theoretically. Sequential losses of SCH2 and CO2 in the ion trap lead to redox reactions with charge transfers between the metal part and the carboxylate and thiolate groups. This allows us to control the number of electrons in the metallic subunit and thus optical properties of the complexes. The presented formation process can be used as a prototype for tuning optical and chemical properties of ligated metal clusters by varying the number of confined electrons within the metallic subunit.

Transition metal-ion complexation is essential to the function and structural stability of many proteins. We studied silver complexation with the octarepeat motif ProHisGlyGlyGlyTrpGlyGln of the prion protein, which shows competitive sites for metal chelation including amide, indole and imidazole groups. This octapeptide is known as a favourable transition metal binding site in prion protein. We used ion mobility spectrometry (IMS), infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations (DFT) to identify the binding motifs of a silver cation on HisGlyGlyGlyTrp peptide as well as on peptide subsequences. Ultra-violet photodissociation (UVPD) and collision induced dissociation mass spectrometry together with the time-dependent density functional method was then exploited to study the influence of binding sites on optical properties and on the ground and excited states reactivity of the peptide. We show that the metal cation is bound to the π-system of the indole group and a nitrogen atom of the imidazole group and that charge transfers from the indole group to the silver cation occur in excited electronic states.

We present the theoretical investigation of structural and optical properties of silver and gold cluster-dipeptide hybrids bound to the F(S) defect of the MgO (100) surface. We use DFT and its TDDFT variant combined with the polarizable embedded cluster model for the description of the extended MgO environment. As model peptide we have chosen CysTrp since the cysteine residue interacts strongly with metal particles through the sulfur atom and tryptophan is the most important chromophoric amino acid. Our results show that in the case of CysTrp bound to the supported Ag(4) cluster an intense optical signal arises at 400 nm. In contrast, in the case of gold no strongly localized absorption is present since the optical response of supported gold-peptide hybrids is dominated by a large number of low intensity d-electron excitations spread over a broad energy range. Such a localized optical signal which is present in supported silver hybrids can be exploited for the optical detection of peptides and thus can serve as basis for the development of biosensing materials.

We focus on the functional role of small silver clusters in model hybrid systems involving peptides in the context of a new generation of nanostructured materials for biosensing. The optical properties of hybrids in the gas phase and at support will be addressed with the aim to bridge fundamental and application aspects. We show that extension and enhancement of absorption of peptides can be achieved by small silver clusters due to the interaction of intense intracluster excitations with the π-π* excitations of chromophoric aminoacids. Moreover, we demonstrate that the binding of a peptide to a supported silver cluster can be detected by the optical fingerprint. This illustrates that supported silver clusters can serve as building blocks for biosensing materials. Moreover, the clusters can be used simultaneously to immobilize biomolecules and to increase the sensitivity of detection, thus replacing the standard use of organic dyes and providing label-free detection. Complementary to that, we show that protected silver clusters containing a cluster core and a shell liganded by thiolates exhibit absorption properties with intense transitions in the visible regime which are also suitable for biosensing applications.

We investigate theoretically the control of the ultrafast excited state dynamics of adenine in water by laser pulse trains, with the aim to extend the excited state lifetime and to suppress nonradiative relaxation processes. For this purpose, we introduce the combination of our field-induced surface hopping method (FISH) with the quantum mechanical-molecular mechanical (QM/MM) technique for simulating the laser-driven dynamics in the condensed phase under explicit inclusion of the solvent environment. Moreover, we employ parametric pulse shaping in the frequency domain in order to design simplified laser pulse trains allowing to establish a direct link between the pulse parameters and the controlled dynamics. We construct pulse trains which achieve a high excitation efficiency and at the same time keep a high excited state population for a significantly extended time period compared to the uncontrolled dynamics. The control mechanism involves a sequential cycling of the population between the lowest and higher excited states, thereby utilizing the properties of the corresponding potential energy surfaces to avoid conical intersections and thus to suppress the nonradiative decay to the ground state. Our findings provide a means to increase the fluorescence yield of molecules with an intrinsically very short excited state lifetime, which can lead to novel applications of shaped laser fields in the context of biosensing.

The replacement of group 10-based materials by superatoms has gained great attention due to studies presenting similarities in electronic character and reactive nature between pairs. The current study extends the concept to systems of larger and varied composition as the pairs PdO(+) and ZrO(2)(+) as well as NiO(+) and TiO(2)(+) are interacted with C(2)H(4) and CO through DFT calculations and guided-ion-beam mass spectrometry. It is determined that the pairs readily oxidize C(2)H(4) while oxygen transfer is limited towards CO. Interestingly, within the reaction profiles for oxidation of C(2)H(4) by PdO(+) and NiO(+), a spin crossover is observed which greatly increases the exothermicity of the process. This investigation presents a major step in identifying replacements for expensive group 10 metals in catalytic materials.

We present the simulation of time-resolved photoelectron spectra of Ag(3) involving excitation from the linear transition state, where nonadiabatic relaxation takes place in a complex manifold of electronic states. Thus, we address ultrafast processes reachable by negative ion-to neutral-to positive ion (NeNePo) spectroscopy starting from the linear Ag anionic species. For this purpose we use our newly developed field-induced surface hopping method (FISH) augmented for the description of photoionization processes. Furthermore we employ our method for nonadiabatic molecular dynamics "on the fly" in the framework of time-dependent density functional theory generalized for open shell systems. Our presented approach is generally applicable for the prediction of time-resolved photoelectron spectra and their analysis in systems with complex electronic structure as well as many nuclear degrees freedom. This theoretical development should serve to stimulate new ultrafast experiments., (© The Owner Societies 2011)

We present the results of a reactivity study of titanium cationic clusters towards CO, C(2)H(2), C(2)H(4) and C(3)H(6) based on guided-ion-beam mass spectrometry and DFT calculations. We identified Ti(2)O(4)(+) and to a lesser extent TiO(2)(+) species which preferentially undergo oxidation reactions. An oxygen centered radical of Ti(2)O(4)(+) is responsible for selective oxidation. Energy profiles and MD simulations reveal the mechanisms of the reactions. Regeneration of the oxygen centered radical was achieved experimentally and theoretically through the reaction of N(2)O with Ti(2)O(3)(+).