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

Effective Quenching and Excited-State Relaxation of a Cu(I) Photosensitizer Addressed by Time-Resolved Spectroscopy and TDDFT Calculations

<p>Homogenous photocatalytic systems based on copper photosensitizers are promising candidates for noble metal free approaches in solar hydrogen generation. To improve their performance a detailed understanding of the individual steps is needed. Here, we study the interaction of a heteroleptic copper (I) photosensitizer with an iron catalyst by time-resolved spectroscopy and ab-initio calculations. The catalyst leads to rather efficient quenching of the ³MLCT state of the copper complex, with a bimolecular rate being about three times smaller than the collision rate. Using control experiments with methyl viologen an appearing absorption band is assigned to the oxidized copper complex demonstrating that electron transfer from the sensitizer to the iron catalyst occurs and the system reacts along an oxidative pathway. However, only about 30% of the quenching events result in an electron transfer while the other 70% experience deactivation indicating that the photocatalytic performance could be improved by optimizing the intermolecular interaction.</p><p><br></p

Strong van der Waals Adhesion of a Polymer Film on Rough Substrates

We propose that chemically inert polymeric films can enhance van der Waals (vdW) forces in the same way as nanofabrication of biomimetic adhesive materials. For the vdW adhesion of an ethylene-chlorotrifluoroethylene (ECTFE) film on rough metal and dielectric substrates, we present a model that combines microscopic quantum-chemistry simulations of the polymer response functions and the equilibrium monomer–substrate distance with a macroscopic quantum-electrodynamics calculation of the Casimir force between the polymer film and the substrate. We predict adhesive forces up to 2.22 kN/mm², where the effect is reduced by substrate roughness and for dielectric surfaces