18 research outputs found
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
Spectroscopic Scanning Tunneling Microscopy Studies of Single Surface-Supported Free-Base Corroles
Stabilisation of tri valent ions with a vacant coordination site at a corrole metal interface
Unraveling the Oxidation and Spin State of Mn Corrole through X ray Spectroscopy and Quantum Chemical Analysis
The
interplay between Mn ions and corrole ligands gives rise to
complex scenarios regarding the metal centers’ electronic properties
expressing a range of high oxidation states and spin configurations.
The resulting potential of Mn–corroles for applications such
as catalysts or fuel cells has recently been demonstrated. However,
despite being crucial for their functionality, the electronic structure
of Mn–corroles is often hardly accessible with traditional
techniques and thus is still under debate, especially under interfacial
conditions. Here, we unravel the electronic ground state of the prototypical
Mn-5,10,15-tris(pentafluorophenyl)corrole complex through X-ray spectroscopic
investigations of ultrapure thin films and quantum chemical analysis.
The theory-based interpretation of Mn photoemission and absorption
fine structure spectra (3s and 2p and L2,3-edge, respectively)
evidence a Mn(III) oxidation state with an S = 2
high-spin configuration. By referencing density functional theory
calculations with the experiments, we lay the basis for extending
our approach to the characterization of complex interfaces
Identifying On Surface Site Selective Chemical Conversions by Theory Aided NEXAFS Spectroscopy The Case of Free Base Corroles on Ag 111
Biofunctionalized conductive polymers enable efficient CO2 electroreduction
Selective electrocatalysts are urgently needed for carbon dioxide (CO2) reduction to replace fossil fuels with renewable fuels, thereby closing the carbon cycle. To date, noble metals have achieved the best performance in energy yield and faradaic efficiency and have recently reached impressive electrical-to-chemical power conversion efficiencies. However, the scarcity of precious metals makes the search for scalable, metal-free, CO2 reduction reaction (CO2RR) catalysts all the more important. We report an all-organic, that is, metal-free, electrocatalyst that achieves impressive performance comparable to that of best-in-class Ag electrocatalysts. We hypothesized that polydopamine-a conjugated polymer whose structure incorporates hydrogen-bonded motifs found in enzymes-could offer the combination of efficient electrical conduction, together with rendered active catalytic sites, and potentially thereby enable CO2RR. Only by developing a vapor-phase polymerization of polydopamine were we able to combine the needed excellent conductivity with thin film-based processing. We achieve catalytic performance with geometric current densities of 18 mA cm(-2) at 0.21 V overpotential (-0.86 V versus normal hydrogen electrode) for the electrosynthesis of C1 species (carbon monoxide and formate) with continuous 16-hour operation at >80% faradaic efficiency. Our catalyst exhibits lower overpotentials than state-of-the-art formate-selective metal electrocatalysts (for example, 0.5 V for Ag at 18 mA cm(-1)). The results confirm the value of exploiting hydrogen-bonded sequences as effective catalytic centers for renewable and cost-efficient industrial CO2RR applications
X ray Spectroscopy of Thin Film Free Base Corroles A Combined Theoretical and Experimental Characterization
Corrole
compounds attract increasing interest due to their potential
to stabilize high-valent metal states. X-ray spectroscopy is a powerful
tool for the investigation and development of functional interfaces.
For corrolic species, however, the required reference data are missing.
Here, we employ a multitechnique X-ray investigation of thin films
of the prototypical free-base 5,10,15-tris(pentafluorophenyl)corrole
(3H-TpFPC) grown on the Ag(111) surface under ultrahigh vacuum conditions.
Ultrapure corrole multilayer samples are prepared and characterized
by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption
fine structure (NEXAFS) spectroscopy. In parallel, the X-ray fingerprints
are simulated using the continued-fraction approach within density
functional theory (DFT) for extended, (quasi-)periodic molecular structures.
An excellent agreement between experimental and theoretical spectra
enables a thorough interpretation of the detailed spectral features
and proves an accurate description of the free-base corrole electronic
structure within the present DFT approach. The present study provides
X-ray spectroscopic references for all relevant core-level regions
and absorption edges of intact molecular species and, thus, represents
an ideal starting point for the comprehensive understanding of the
complex chemistry of corroles in the adsorbed state toward the development
of related functional interfaces
Photoinduced refractive-index change in 4-tert-butylcalix[8]arenes bearing N-acyloxyphenylamide chromophores
On Surface Site Selective Cyclization of Corrole Radicals
Radical
cyclization is among the most powerful and versatile reactions
for constructing mono- and polycyclic systems, but has, to date, remained
unexplored in the context of on-surface synthesis. We report the controlled
on-surface synthesis of stable corrole radicals on Ag(111) <i>via</i> site-specific dehydrogenation of a pyrrole N–H
bond in the 5,10,15-tris(pentafluoro-phenyl)-corrole triggered by
annealing at 330 K under ultrahigh-vacuum conditions. We reveal a
thermally induced regioselective cyclization reaction mediated by
a radical cascade and resolve the reaction mechanism of the pertaining
cyclodefluorination reaction at the single-molecule level. <i>Via</i> intramolecularly resolved probing of the radical-related
Kondo signature, we achieve real space visualization of the distribution
of the unpaired electron density over specific sites within the corrole
radical. Annealing to 550 K initiates intermolecular coupling reactions,
producing an extended π-conjugated corrole system