13 research outputs found
Tuning Range-Separated Density Functional Theory for Photocatalytic Water Splitting Systems
We discuss the system-specific optimization
of long-range-separated
density functional theory (DFT) for the prediction of electronic properties
relevant for a photocatalytic cycle based on an Ir(III) photosensitizer
(IrPS). Special attention is paid to the charge-transfer properties,
which are of key importance for the photoexcitation dynamics but cannot
be correctly described by means of conventional DFT. The optimization
of the range-separation parameter using the ΔSCF method is discussed
for IrPS including its derivatives and complexes with electron donors
and acceptors used in photocatalytic hydrogen production. Particular
attention is paid to the problems arising for a description of medium
effects by means of a polarizable continuum model
Electron- and Energy-Transfer Processes in a Photocatalytic System Based on an Ir(III)-Photosensitizer and an Iron Catalyst
The
reaction pathways of bis-(2-phenylpyridinato-)(2,2′-bipyridine)iridium(III)hexafluorophosphate
[Ir(ppy)<sub>2</sub>(bpy)]PF<sub>6</sub> within a photocatalytic water
reduction system for hydrogen generation based on an iron-catalyst
were investigated by employing time-resolved photoluminescence spectroscopy
and time-dependent density functional theory. Electron transfer (ET)
from the sacrificial reagent to the photoexcited Ir complex has a
surprisingly low probability of 0.4% per collision. Hence, this step
limits the efficiency of the overall system. The calculations show
that ET takes place only for specific encounter geometries. At the
same time, the presence of the iron-catalyst represents an energy
loss channel due to a triplet–triplet energy transfer of Dexter
type. This loss channel is kept small by the employed concentration
ratios, thus favoring the reductive ET necessary for the water reduction.
The elucidated reaction mechanisms underline the further need to improve
the sun light’s energy pathway to the catalyst to increase
the efficiency of the photocatalytic system
Chemical Bonding in Aqueous Ferrocyanide: Experimental and Theoretical X‑ray Spectroscopic Study
Resonant inelastic X-ray scattering
(RIXS) and X-ray absorption
(XA) experiments at the iron L- and nitrogen K-edge are combined with
high-level first-principles restricted active space self-consistent
field (RASSCF) calculations for a systematic investigation of the
nature of the chemical bond in potassium ferrocyanide in aqueous solution.
The atom- and site-specific RIXS excitations allow for direct observation
of ligand-to-metal (Fe L-edge) and metal-to-ligand (N K-edge) charge-transfer
bands and thereby evidence for strong σ-donation and π-backdonation.
The effects are identified by comparing experimental and simulated
spectra related to both the unoccupied and occupied molecular orbitals
in solution