First time combination of frozen density embedding theory with the algebraic diagrammatic construction scheme for the polarization propagator of second order.

The combination of Frozen Density Embedding Theory (FDET) and the Algebraic Diagrammatic Construction (ADC) scheme for the polarization propagator for describing environmental effects on electronically excited states is presented. Two different ways of interfacing and expressing the so-called embedding operator are introduced. The resulting excited states are compared with supermolecular calculations of the total system at the ADC(2) level of theory. Molecular test systems were chosen to investigate molecule-environment interactions of varying strength from dispersion interaction up to multiple hydrogen bonds. The overall difference between the supermolecular and the FDE-ADC calculations in excitation energies is lower than 0.09 eV (max) and 0.032 eV in average, which is well below the intrinsic error of the ADC(2) method itself.

Chiral thiahelicene-based alkyl phosphine-borane complexes: synthesis, X-ray characterization, and theoretical and experimental investigations of optical properties.

Chiral helical-based phosphanes are challenging and promising ligands, with a great potential for the generation of both organic and organometallic catalysts. We report here the preparation of novel chiral thiahelicene-based alkyl phosphanes, isolated and characterized as air-stable borane adducts, and the investigation of their experimental and theoretical (chir)optical properties. X-ray characterization of a mono- and a disubstituted derivative as a racemic mixture has been performed, which confirms the influence of the number and nature of substituents on the flexibility of the helix. In addition, the absolute configuration inferred from CD spectra of the two enantiomers of a diborane complex has been established from X-ray analysis. State-of-the-art quantum chemical calculations of vibrationally resolved spectra allow, for the first time, for an unambiguous assignment of the experimentally observed peaks in linear absorption and circular dichroism spectra to excited electronic states of this class of thiahelicene phosphorus derivatives.

Ultrafast C(Spiro)-O dissociation via a conical intersection drives spiropyran to merocyanine photoswitching.

The mechanism of the photochemical conversion of spiropyran to merocyanine is investigated theoretically. Calculations were performed at TD-DFT/ωB97XD/cc-pVDZ level of theory, which shows good agreement with the reference RI-CC2 method. A two-dimensional scan of the potential energy surface has been performed along the C-O distance and the central torsion angle in the ground state and in the first excited state, where the reaction takes place. Starting at the Franck-Condon geometry, the energy of the first excited state decreases in the direction of the C-O dissociation while the ground-state energy increases. This leads to a barrierless C-O bond dissociation in the first excited state. While relaxing on the S1 PES toward longer C-O distances, the torsion angle hardly changes, but other coordinates start to vary, leading to a conical intersection of the ground state and the first excited state at a C-O distance of about 3.4 Å. Passing the conical intersection, the reaction continues on the ground-state PES. At these large C-O distances, either barrierless Cspiro-O rebinding occurs that quenches spiropyran isomerization or rotation around the central torsion angle occurs that leads to merocyanine. For the latter an energy barrier of 0.1 eV must be overcome explaining the low quantum yield of spiropyran to merocyanine photoswitching.

Gold(I) complexes of tetrathiaheterohelicene phosphanes.

New tetrathia[7]helicene-based (7-TH-based) gold(I) complexes 6 and 7 have been readily prepared by reaction of the respective phosphine ligands 2 and 3 with Au(tht)Cl in a 1:1 and 1:2 molar ratio, respectively. These complexes have been fully characterized by analytical and spectroscopic techniques as well as quantum chemical calculations. The molecular structure of dinuclear complex 7 has been determined by single-crystal X-ray diffraction, showing a gold-gold interaction of 3.1825(3) Å and a significant contraction of the 7-TH total dihedral angle. Au(I) complex 7 displays luminescence emission at room and low temperature in diluted solution and in the solid state. Quantum chemical calculations show that the luminescence emission at room temperature is primarily due to slightly perturbed fluorescence emission from purely ππ* excited states of the conjugated helicene scaffold. At 77 K phosphorescence emission is displayed as well. Preliminary studies on the use of 6 and 7 as catalysts in typical Au(I)-catalyzed cycloisomerizations have demonstrated the reactivity of these systems in the intramolecular allene hydroarylations and the hydroxycarboxylation of allene-carboxylates.

Benchmark of Excitation Energy Shifts from Frozen-Density Embedding Theory: Introduction of a Density-Overlap-Based Applicability Threshold.

We present a thorough investigation of the errors in results obtained with the combination of frozen-density embedding theory and the algebraic diagrammatic construction scheme for the polarization propagator of second order (FDE-ADC(2)). The study was carried out on a set of 52 intermolecular complexes with varying interaction strength, each consisting of a chromophore of fundamental interest and a few small molecules in its environment. The errors emerging in frozen-density embedding theory-based methods originate from (a) the solver of the quantum many-body problem used to obtain the embedded wave function (ΨAemb), (b) the approximation for the explicit density functional for the embedding potential, and (c) the choice of the density representing the environment (ρB( r⃗)). The present work provides a comprehensive analysis of the errors in the excitation energies based on the last two factors. Furthermore, a density-overlap-based parameter is proposed to be used as an a priori criterion of applicability.

Helical push-pull systems for solar cells: Electrochemical, computational, photovoltaic and NMR data.

The data presented in this article are related to the research article entitled "An unconventional helical push-pull system for solar cells" (Dova et al., 2019). This article provides: a) the cyclic voltammogram plots in solution of helical push-pull sensitizers and the corresponding precursors; b) the visualization of the leading natural transition orbital (NTO) pairs obtained by theoretical calculation of frontiers orbitals; c) J/V curves of dye-sensitized solar cells (DSSC) sensitized by the dyes, without 3a,7a-dihydroxy-5b-cholic acid (CDCA) as co-adsorbent agent; d) 1H and 13C NMR spectra of dyes.

Implementation and Application of the Frozen Density Embedding Theory with the Algebraic Diagrammatic Construction Scheme for the Polarization Propagator up to Third Order.

Implementation, benchmarking, and representative applications of the new FDE-ADC(3) method for describing environmental effects on excited states as a combination of frozen density embedding (FDE) and the algebraic-diagrammatic construction scheme for the polarization propagator of third order (ADC(3)) are presented. Results of FDE-ADC(3) calculations are validated with respect to supersystem calculations on test systems with varying molecule-environment interaction strengths from dispersion up to multiple hydrogen bonds. The overall deviation compared to the supersystem calculations is as small as 0.029 eV for excitation energies, which is even smaller than the intrinsic error of ADC(3). The dependence of the accuracy on the choice of method and functional for the calculation of the environment and the nonelectrostatic part of the system-environment interaction is evaluated. In three representative examples, the FDE-ADC method is applied to investigate larger systems and to analyze excited state properties using visualization of embedded densities and orbitals.