Computing UV/vis spectra using a combined molecular dynamics and quantum chemistry approach: bis-triazin-pyridine (BTP) ligands studied in solution

Automated Generation of Optimized Auxiliary Basis Sets for Long-Range-Corrected TDDFT Using the Cholesky Decomposition

Range-separated hybrid functionals making use of a smooth separation of the Coulomb operator in terms of the error function and its complement have proven to be a valuable tool for improving Kohn-Sham density functional theory (DFT) calculations. This holds in particular for obtaining accurate excitation energies from linear-response time-dependent DFT. Evaluating the long-range exchange contributions represents one of the most time-consuming tasks in such calculations. Prefitted auxiliary basis sets can be employed to speed up this step. Here, we present a way to generate auxiliary basis sets optimized to fit the long-range exchange contributions only, contrary to the common optimization strategies on the basis of the full Coulomb operator. For this purpose, we use the atomic Cholesky decomposition technique. The basis sets are generated on-the-fly using the specific range-separation parameter defined in the exchange-correlation functional. We obtain excitation energies and oscillator strengths which are of similar or better accuracy than those obtained with conventional resolution-of-the-identity auxiliary basis sets while drastically reducing the number of auxiliary functions required. This is demonstrated for the QUESTDB#5 benchmark set. In addition, we outline the benefits of this approach in sequences of calculations employing varying range-separation parameters, as is the case in the optimally tuned range-separation strategy. Finally, we illustrate the efficiency of this approach for real-world examples, namely, a chlorophyll tetramer from photosystem II and a carotenoid-porphyrin-C₆₀ triad.

A combined approach of electronic spectroscopy and quantum chemical calculations to assess model membrane oxidation pathways

Assessment of lipid oxidation pathways using UV spectroscopy and quantum chemical calculations.

Synthesis of soft N-donor isoPentyl-BTBP and study on its removal of actinides from high level liquid waste

To directly separate actinides from high level liquid waste (HLLW), a novel molecule, i. e. isoPentyl-BTBP (6,6′-bis(5,6-bis(4-methylpentyl)-1,2,4-triazin-3-yl)-2,2′-bipyridines) was synthesized and characterized. A kind of isoPentyl-BTBP/SiO2-P adsorbent was obtained by impregnating isoPentyl-BTBP into porous silica/polymer support particles SiO2-P under reduced pressure. The effect of HNO3 concentration, contact time on the adsorption of isoPentyl-BTBP/SiO2-P towards 241Am(III) and 239Pu(IV) was studied. And the stability of isoPentyl-BTBP/SiO2-P in HNO3 medium was also evaluated. It turned out that isoPentyl-BTBP/SiO2-P had much higher affinity for 241Am(III) and 239Pu(IV) over FP elements in 3 M HNO3, fast adsorption kinetics towards 239Pu(IV), excellent stability in HNO3 medium, and should be a very promising adsorbent for separating 239Pu(IV) and 241Am(III) from HLLW.

Activation of the Aromatic Core of 3,3'-(Pyridine-2,6-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol)-Effects on Extraction Performance, Stability Constants, and Basicity

The "CHON" compatible water-soluble ligand 3,3'-(pyridine-2,6-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PTD) has shown promise for selectively stripping actinide ions from an organic phase containing both actinide and lanthanide ions, by preferential complexation of the former. Aiming at improving its complexation properties, PTD-OMe was synthesized, bearing a methoxy group on the central pyridine ring, thus increasing its basicity and hence complexation strength. Unfortunately, solvent extraction experiments in the range of 0.1-1 mol/L nitric acid proved PTD-OMe to be less efficient than PTD. This behavior is explained by its greater pK_a value (pK_a = 2.54) compared to PTD (pK_a = 2.1). This counteracts its improved complexation properties for Cm(III) (log β₃(PTD-OMe) = 10.8 ± 0.4 versus log β₃(PTD) = 9.9 ± 0.5).

Analytical Nuclear Excited-State Gradients for the Second-Order Approximate Coupled-Cluster Singles and Doubles (CC2) Method Employing Uncoupled Frozen-Density Embedding

We report the derivation and implementation of analytical orbital-relaxed properties and nuclear gradients for excited states using the second-order approximate coupled-cluster singles and doubles (CC2) model combined with uncoupled frozen-density embedding (FDEu). An implementation of the algebraic diagrammatic construction through second-order ADC(2), which arises from simplification of RICC2 FDEu, is also presented. In order to ensure a RICC2 FDEu Lagrange functional that is linear in the Lagrange multipliers, the Hartree-Fock density is employed for the target subsystem in the embedding contributions. The accuracy of the new scheme is assessed using the carbon monoxide molecule, 4-aminophthalimide, and a benzonitrile dimer, revealing that the obtained errors are below the method error of RICC2. Using density functional theory for the environment, the efficiency of the new method is illustrated by computing the perturbed excited-state dipole moment of a chromophore in a biological environment. For this system, comprising 32 molecules consisting of 366 atoms in total, the computation requires only a couple of days on a standard compute node. RICC2 FDEu thus enables large-scale calculations of ab initio wave functions for molecules in complex environments as routine applications.

Bismuth as a versatile cation for luminescence in coordination polymers from BiX3/4,4'-bipy: understanding of photophysics by quantum chemical calculations and structural parallels to lanthanides

Coordination polymers (CPs) with bismuth(iii) as a connectivity centre have been prepared from BiX3 (X = Cl-I) and 4,4'-bipyridine (bipy) in order to implement Bi-based luminescence. The products were obtained via different synthetic routes such as solution chemistry, melt syntheses or mechanochemical reactions. Five neutral and anionic 1D-CPs are presented that show a chemical parallel to trivalent lanthanides forming isostructural or closely related 1D-CPs, of which five additional compounds are described. Bi3+ proves to be a versatile cation for luminescence resulting from energy transfer processes between a metal and a ligand in the presented CPs. Quantum chemical calculations were carried out to investigate Bi3+-participation in the luminescence processes. The calculated results allow an assignment of the bright transitions composed of mainly metal-to-ligand-charge transfer (MLCT) character. These results show that Bi3+ can form strongly luminescent coordination compounds with N-donor ligands.

Unexpected solvent effects on the UV/Vis absorption spectra of o-cresol in toluene and benzene: in contrast with non-aromatic solvents

Cresol is a prototype molecule in understanding intermolecular interactions in material and biological systems, because it offers different binding sites with various solvents and protonation states under different pH values. It is found that the UV/Vis absorption spectra of o-cresol in aromatic solvents (benzene, toluene) are characterized by a sharp peak, unlike the broad double-peaks in 11 non-aromatic solvents. Both molecular dynamics simulations and electronic structure calculations revealed the formation of intermolecular π-complexation between o-cresol and aromatic solvents. The thermal movements of solvent and solute molecules render the conformations of o-cresol changing between trans and cis isomers. The π-interaction makes the cis configuration a dominant isomer, hence leading to the single keen-edged UV/Vis absorption peak at approximately 283 nm. The free conformation changes between trans and cis in aqueous solution rationalize the broader absorption peaks in the range of 260-280 nm. The pH dependence of the UV/Vis absorption spectra in aqueous solutions is also rationalized by different protonation states of o-cresol. The explicit solvent model with long-ranged interactions is vital to describe the effects of π-complexation and electrostatic interaction on the UV/Vis absorption spectra of o-cresol in toluene and alkaline aqueous (pH > 10.3) solutions, respectively.

Analytical nuclear excited-state gradients for the Tamm-Dancoff approximation using uncoupled frozen-density embedding

We report the derivation and implementation of analytical nuclear gradients for excited states using time-dependent density functional theory using the Tamm-Dancoff approximation combined with uncoupled frozen-density embedding using density fitting. Explicit equations are presented and discussed. The implementation is able to treat singlet as well as triplet states and functionals using the local density approximation, the generalized gradient approximation, combinations with Hartree-Fock exchange (hybrids), and range-separated functionals such as CAM-B3LYP. The new method is benchmarked against supermolecule calculations in two case studies: The solvatochromic shift of the (vertical) fluorescence energy of 4-aminophthalimide on solvation, and the first local excitation of the benzonitrile dimer. Whereas for the 4-aminophthalimide-water complex deviations of about 0.2 eV are obtained to supermolecular calculations, for the benzonitrile dimer the maximum error for adiabatic excitation energies is below 0.01 eV due to a weak coupling of the subsystems. © 2017 Wiley Periodicals, Inc.

Exploring the optical reporting characteristics of drugs: UV-Vis spectra and conformations of the tyrosine kinase inhibitor SKF86002

The ultimate understanding of drug–protein interactions relies on understanding drug behaviours in solution, at the molecular level.

4,4′-Di-tert-butyl-6-(1H-tetrazol-5-yl)-2,2′-bipyridine: modification of a highly selective N-donor ligand for the separation of trivalent actinides from lanthanides

In the present work, the complexation and extraction behaviour of HN₄^tbubipy towards An(iii) and Ln(iii) is studied by spectroscopy, solvent extraction, and QM calculations.

Importance of Vibronic Effects in the UV-Vis Spectrum of the 7,7,8,8-Tetracyanoquinodimethane Anion

We present a computational method for simulating vibronic absorption spectra in the ultraviolet-visible (UV-vis) range and apply it to the 7,7,8,8-tetracyanoquinodimethane anion (TCNQ^-), which has been used as a ligand in black absorbers. Gaussian broadening of vertical electronic excitation energies of TCNQ^- from linear-response time-dependent density functional theory produces only one band, which is qualitatively incorrect. Thus, the harmonic vibrational modes of the two lowest doublet states were computed, and the vibronic UV-vis spectrum was simulated using the displaced harmonic oscillator approximation, the frequency-shifted harmonic oscillator approximation, and the full Duschinsky formalism. An efficient real-time generating function method was implemented to avoid the exponential complexity of conventional Franck-Condon approaches to vibronic spectra. The obtained UV-vis spectra for TCNQ^- agree well with experiment; the Duschinsky rotation is found to have only a minor effect on the spectrum. Born-Oppenheimer molecular dynamics simulations combined with calculations of the electronic excitation energies for a large number of molecular structures were also used for simulating the UV-vis spectrum. The Born-Oppenheimer molecular dynamics simulations yield a broadening of the energetically lowest peak in the absorption spectrum, but additional vibrational bands present in the experimental and simulated quantum harmonic oscillator spectra are not observed in the molecular dynamics simulations. Our results underline the importance of vibronic effects for the UV-vis spectrum of TCNQ^-, and they establish an efficient method for obtaining vibronic spectra using a combination of linear-response time-dependent density functional theory and a real-time generating function approach.

2,6-Bis(5,6-diisopropyl-1,2,4-triazin-3-yl)pyridine: a highly selective N-donor ligand studied by TRLFS, liquid–liquid extraction and molecular dynamics

Studying the effect of modifications of BTP-ligands on the complexation and separation of Ln(iii) and An(iii).