Preserving Charge and Oxidation State of Au(III) Ions in an Agent-Functionalized Nanocrystal Model System

Supporting functional molecules on crystal facets is an established technique in nanotechnology. To preserve the original activity of ionic metallorganic agents on a supporting template, conservation of the charge and oxidation state of, the active center is indispensable. We. present a model system of a metallorganic agent that, indeed, fulfills this design criterion on a technologically relevant metal support With potential Impact on Au(III)-porphyrin-functionalized nanoparticles for an improved anticancer-drug delivery. Employing scanning tunneling microscopy and -spectroscopy in combination with photoemission spectroscopy,we clarify at the single-molecule level the underlying mechanisms of this exceptional adsorption mode. It is based on the balance between a high-energy oxidation state and an electrostatic screening-response of the surface (image charge). Modeling with first principles methods reveals submolecular details of the metal-ligand bonding interaction and completes the study by providing an Illustrative electrostatic.. model relevant for ionic metalorganic agent molecules, in general

Computational Study of Structures and Electronic Properties of Metal Clusters

Subnanometer sized transition metal clusters have attracted a great deal of interest in recent years. In this thesis we have investigated the structures, electronic and optical properties, the structural evolution due to doping with a heteroatom, and the catalytic activity of subnanometer sized Aun (n = 2-20) clusters using various computational methods. Another major theme of this thesis has been to understand the mechanisms of organic reactions such as C–C coupling and cycloisomerization reactions triggered by transition metal complexes. We have reported electronic and chemical properties of novel 2D materials such as fluorographene, germanene, and germanane. One future extension of this work shall be the investigation of metal clusters anchored on these 2D systems for designing heterogeneous catalysts for vital organic transformations, which has been studied in the presence of naked metal clusters and metal complexes in the present thesis.Research was carried out under the supervision of Prof. Ayan Dutta of Spectroscopy division under SPS [School of Physical Sciences]Research was conducted under IACS fellowship and DST gran

Mechanism for C–I Bond Dissociation in Iodoethane, Iodobenzene, and Iodoethene for the C–C Cross Coupling Reactions over Gold Clusters

The mechanisms for the C–I bond dissociation in iodoethane, iodobenzene, and iodoethene over the subnanometer sized gold clusters were studied using density functional theory. Au₃, Au₄, Au₁₄, and Au₂₀ clusters and their cations were used as the models to investigate the effects of the size, geometry, and electronic charge on the catalysis of the reaction. Our calculations predict that both iodoethane and iodobenzene interact with the gold through the lone pair on iodine with the small planar clusters activating the reaction more effectively through the formation of strong adducts and low barrier heights. Clusters with large HOMO–LUMO gaps act as poor catalysts owing to the quantum size effects. Even though the cationic clusters bind to the reactants more strongly due to their enhanced Lewis acidity, they also require higher activation energy. However, the catalysis by cations and 3D clusters has a smaller endergonicity which would be desirable in the subsequent steps in cross/homo coupling reactions. In the case of iodoethene, gold binds through the π electrons instead of the lone pair on iodine which fine-tunes the bond dissociation process

Criticality of Symmetry in Rational Design of Chalcogenide Perovskites

Chalcogenide perovskites constitute an emerging class of promising photovoltaic materials that are stable and less toxic than popular lead-halide perovskites. Transition-metal and chalcogenide doping are the possible strategies for improving the photovoltaic properties of these materials via the band gap engineering. At the same time, doping can facilitate nonradiative charge-carrier recombination in these materials, adversely affecting their photovoltaic properties. We report a systematic study of electronic structure and nonadiabatic dynamics in transition-metal- and chalcogenide-doped barium-zirconium-sulfide-based perovskites. The potential of these doping strategies to modulate the performance of photovoltaic materials is explored. Through the detailed analysis of the factors affecting the dynamics, we illustrate how symmetry (both structural and orbital) and decoherence can be critical to furnishing the most favorable properties. The noted factors of symmetry and decoherence may provide new rational design principles for efficient photovoltaics

Criticality of Symmetry in Rational Design of Chalcogenide Perovskites

Chalcogenide perovskites constitute an emerging class of promising photovoltaic materials that are stable and less toxic than popular lead-halide perovskites. Transition-metal and chalcogenide doping are the possible strategies for improving the photovoltaic properties of these materials via the band gap engineering. At the same time, doping can facilitate nonradiative charge-carrier recombination in these materials, adversely affecting their photovoltaic properties. We report a systematic study of electronic structure and nonadiabatic dynamics in transition-metal- and chalcogenide-doped barium-zirconium-sulfide-based perovskites. The potential of these doping strategies to modulate the performance of photovoltaic materials is explored. Through the detailed analysis of the factors affecting the dynamics, we illustrate how symmetry (both structural and orbital) and decoherence can be critical to furnishing the most favorable properties. The noted factors of symmetry and decoherence may provide new rational design principles for efficient photovoltaics

Aminoindolines versus Quinolines: Mechanistic Insights into the Reaction between 2-Aminobenzaldehydes and Terminal Alkynes in the Presence of Metals and Secondary Amines

DFT computational studies in the cyclization of aminoalkyne (see structure), which is generated in situ by 2-aminobenzaldehydes and terminal alkynes in the presence of metals and secondary amines, has been investigated. The study revealed that the mode of cyclization (<i>exo</i> vs <i>endo</i>) depends on the protecting group on nitrogen, the oxidation state of copper, and substitution on alkyne

Molecular Balances Based on Aliphatic CH−π and Lone-Pair−π Interactions

CH···π and lone-pair···π interactions are estimated for a series of conformationally dynamic bicyclic <i>N</i>-aryliimides. On the basis of their strengths and mutual synergy/competition, the molecules prefer a folded/unfolded conformation. Calculations suggest strategies to selectively isolate the folded form by increasing the strength of the attractive CH···π interaction or removing the lone-pair···π repulsion. While the barrier for the folded ⇄ unfolded transformation is too large to conformationally lock the molecules in either of the conformers, the dynamics for hopping of the alkyl group across rings and tumbling over the rings are found to be facile in the folded conformation

Molecular Balances Based on Aliphatic CH−π and Lone-Pair−π Interactions

CH···π and lone-pair···π interactions are estimated for a series of conformationally dynamic bicyclic <i>N</i>-aryliimides. On the basis of their strengths and mutual synergy/competition, the molecules prefer a folded/unfolded conformation. Calculations suggest strategies to selectively isolate the folded form by increasing the strength of the attractive CH···π interaction or removing the lone-pair···π repulsion. While the barrier for the folded ⇄ unfolded transformation is too large to conformationally lock the molecules in either of the conformers, the dynamics for hopping of the alkyl group across rings and tumbling over the rings are found to be facile in the folded conformation

Molecular Balances Based on Aliphatic CH−π and Lone-Pair−π Interactions

CH···π and lone-pair···π interactions are estimated for a series of conformationally dynamic bicyclic <i>N</i>-aryliimides. On the basis of their strengths and mutual synergy/competition, the molecules prefer a folded/unfolded conformation. Calculations suggest strategies to selectively isolate the folded form by increasing the strength of the attractive CH···π interaction or removing the lone-pair···π repulsion. While the barrier for the folded ⇄ unfolded transformation is too large to conformationally lock the molecules in either of the conformers, the dynamics for hopping of the alkyl group across rings and tumbling over the rings are found to be facile in the folded conformation