7 research outputs found
Controlled Surface-Assembly of Nanoscale Leaf-Type Cu-Oxide Electrocatalyst for High Activity Water Oxidation
The controlled surface deposition
of a robust and high-performance
nanostructured copper-oxide (<b>CuO</b><sub><b>x</b></sub>-NLs) electrocatalyst for water oxidation is presented. The material
exhibits a characteristic leaf-type morphology and self-assembles
on a copper substrate by straightforward constant-current anodization.
The oxygen onset occurs at about 1.55 V versus RHE (η = 320
mV), which is 400â500 mV less than for amorphous Cu-oxide films.
A Tafel slope of 44 mV dec<sup>â1</sup> is obtained, which
is the lowest observed relative to other copper-based materials. Long-term
catalytic performance and stability tests of the electrocatalytic <b>CuO</b><sub><b>x</b></sub>-NLs sample show a stable current
density of >17 mA cm<sup>â2</sup> for oxygen evolution,
which
was sustained for many hours
In-Silico Design of a DonorâAntennaâAcceptor Supramolecular Complex for Photoinduced Charge Separation
We
investigate via density functional theory a series of donorâantennaâacceptor
molecular rectifiers designed as modules for artificial photosynthesis
devices. We consider triad modules containing phenothiazine (PTZ)
as the electron donor and different derivatives of naphthalene diimide
(NDI) as the antenna and secondary electron acceptor. The choice of
the molecular components in the triad is guided by the redox and optical
properties of each subunit. Using time-dependent DFT in combination
with the long-range corrected xc-functional CAM-B3LYP we investigate
how photoinduced charge transfer states are affected by systematic
modifications of the triad molecular structure. In particular, we
show how by controlling the length of the molecular bridges connecting
the different charge separator subunits it is possible to control
the driving force for the relaxation of the excitonic state into the
full charge-separated state. On the basis of these findings we propose
a supramolecular triad consisting of inexpensive and readily available
molecular components that can find its implementation in artificial
devices for solar energy transduction
A Dynamic View of Proton-Coupled Electron Transfer in Photocatalytic Water Splitting
Solar-driven
water splitting is a key reaction step in a photoelectrochemical
cell for solar fuel production. We propose a photoanode in which a
TiO<sub>2</sub> substrate is functionalized with a supramolecular
complex consisting of a fully organic naphthalene-diimide (NDI) dye
covalently bound to a mononuclear Ru-based water oxidation catalyst.
By performing ab initio Molecular Dynamics simulations, we elucidate
microscopic details of water oxidation at the photoanode induced by
visible light absorption. The fast photoinduced electron injection
from the NDI into the semiconductor provides the driving force for
the activation of the Ru catalyst. The proton-coupled electron transfer
nature of this catalytic reaction path is unveiled through the explicit
description of the water environment, which is essential to determine
the proton diffusion channel and the free energy change along the
reaction. The mechanistic insight into the photocatalytic processes
obtained with our computational strategy can facilitate the design
of new and efficient photoelectrochemical devices
Structure Determination of a Bio-Inspired Self-Assembled Light-Harvesting Antenna by Solid-State NMR and Molecular Modeling
The
molecular stacking of an artificial light-harvesting antenna
self-assembled from 3<sup>1</sup>-aminofunctionalized zinc-chlorins
was determined by solid-state NMR in combination with quantum-chemical
and molecular-mechanics modeling. A library of trial molecular stacking
arrangements was generated based on available structural data for
natural and semisynthetic homologues of the Zn-chlorins. NMR assignments
obtained for the monomer in solution were validated for self-assembled
aggregates and refined with <sup>1</sup>Hâ<sup>13</sup>C heteronuclear
correlation spectroscopy data collected from samples with <sup>13</sup>C at natural abundance. Solid-state ring-current shifts for the <sup>1</sup>H provided spatial constraints to determine the molecular
overlap. This procedure allows for a discrimination between different
self-assembled structures and a classification of the stacking mode
in terms of electric dipole alignment and ÏâÏ interactions,
parameters that determine the functional properties of light-harvesting
assemblies and conducting nanowires. The combination with quantum-mechanical
modeling then allowed building a low-resolution packing model in silico
from molecular stacks. The method allows for moderate disorder and
residual polymorphism at the stack or molecular level and is generally
applicable to determine molecular packing structures of aromatic molecules
with structural asymmetry, such as is commonly provided by functionalized
side chains that serve to tune the self-assembly process
Crucial Role of Nuclear Dynamics for Electron Injection in a DyeâSemiconductor Complex
We investigate the electron injection
from a terrylene-based chromophore
to the TiO<sub>2</sub> semiconductor bridged by a recently proposed
phenyl-amide-phenyl molecular rectifier. The mechanism of electron
transfer is studied by means of quantum dynamics simulations using
an extended HuÌckel Hamiltonian. It is found that the inclusion
of the nuclear motion is necessary to observe the photoinduced electron
transfer. In particular, the fluctuations of the dihedral angle between
the terrylene and the phenyl ring modulate the localization and thus
the electronic coupling between the donor and acceptor states involved
in the injection process. The electron propagation shows characteristic
oscillatory features that correlate with interatomic distance fluctuations
in the bridge, which are associated with the vibrational modes driving
the process. The understanding of such effects is important for the
design of functional dyes with optimal injection and rectification
properties
On the Morphology of a Discotic Liquid Crystalline Charge Transfer Complex
Discotic liquid crystalline (DLC) charge transfer (CT)
complexes, which combine visible light absorption with rapid charge
transfer characteristics within the CT complex, can have a great potential
for photovoltaic applications when they can be made to self-assemble
in a bulk heterojunction arrangement with separate channels for electron
and hole conduction. However, the morphology of some liquid crystalline
CT complexes has been under debate for many years. In particular,
the liquid crystalline CT complex built from the electron acceptor
2,4,7-trinitro-9-fluorenone (TNF) and discotic molecules has been
reported to have the TNF âsandwichedâ either between
the discotic molecules within the same column or between the columns
within the aliphatic tails of the discotic molecules. We present a
detailed structural study of the prototypic 1:1 mixture of the discotic
2,3,6,7,10,11-hexakisÂ(hexyloxy)Âtriphenylene (HAT6) and TNF. Nuclear
magnetic resonance (NMR) line widths and cross-polarization rates
are consistent with the picosecond time scale anisotropic thermal
motions of the HAT6 and TNF molecules previously observed. By computational
integration of Rietveld refinement analyses of neutron diffraction
patterns with density experiments and short-range structural constraints
from heteronuclear 2D NMR, we determine that the TNF molecules are
vertically oriented between HAT6 columns. The data provide the insight
that a morphology of separate hole conducting channels of HAT6 molecules
can be realized in the liquid crystalline CT complex
Structural Variability in Wild-Type and <i>bchQ bchR</i> Mutant Chlorosomes of the Green Sulfur Bacterium <i>Chlorobaculum tepidum</i>
The self-aggregated state of bacteriochlorophyll (BChl) <i>c</i> molecules in chlorosomes belonging to a <i>bchQ bchR</i> mutant of the green sulfur bacteria <i>Chlorobaculum tepidum</i>, which mostly produces a single 17<sup>2</sup>-farnesyl-(<i>R</i>)-[8-ethyl,12-methyl]ÂBChl <i>c</i> homologue,
was characterized by solid-state nuclear magnetic resonance (NMR)
spectroscopy and high-resolution electron microscopy. A nearly complete <sup>1</sup>H and <sup>13</sup>C chemical shift assignment was obtained
from well-resolved homonuclear <sup>13</sup>Câ<sup>13</sup>C and heteronuclear <sup>1</sup>Hâ<sup>13</sup>C NMR data
sets collected from <sup>13</sup>C-enriched chlorosome preparations.
Pronounced doubling (1:1) of specific <sup>13</sup>C and <sup>1</sup>H resonances revealed the presence of two distinct and nonequivalent
BChl <i>c</i> components, attributed to all <i>syn-</i> and all <i>anti</i>-coordinated parallel stacks, depending
on the rotation of the macrocycle with respect to the 3<sup>1</sup>-methyl group. Steric hindrance from the 20-methyl functionality
induces structural differences between the <i>syn</i> and <i>anti</i> forms. A weak but significant and reproducible reflection
at 1/0.69 nm<sup>â1</sup> in the direction perpendicular to
the curvature of cylindrical segments observed with electron microscopy
also suggests parallel stacking of BChl <i>c</i> molecules,
though the observed lamellar spacing of 2.4 nm suggests weaker packing
than for wild-type chlorosomes. We propose that relaxation of the
pseudosymmetry observed for the wild type and a related BChl <i>d</i> mutant leads to extended domains of alternating <i>syn</i> and <i>anti</i> stacks in the <i>bchQ
bchR</i> chlorosomes. Domains can be joined to form cylinders
by helical <i>synâanti</i> transition trajectories.
The phase separation in domains on the cylindrical surface represents
a basic mechanism for establishing suprastructural heterogeneity in
an otherwise uniform supramolecular scaffolding framework that is
well-ordered at the molecular level