Theoretical study on oligothiophene N-succinimidyl esters: size and push-pull effects

We report a theoretical study on the optical properties of bithiophene and terthiophene N-succinimidyl esters, which have been functionalized with a methylsulfanyl group in the alpha or the beta positions. Time-dependent density functional theory (TD-DFT) and approximate coupled-cluster singles and doubles with the resolution of identity technique (RI-CC2) calculations have been performed in the ground and excited states. The RI-CC2 results for absorption and fluorescence energies are in better qualitative agreement with experiments, whereas TD-DFT does not correctly describe the higher energy part of the absorption spectra of beta-substituted bithiophenes, due to the presence of charge-transfer states. Systems functionalized at the alpha position show a large red-shift of the main absorption and fluorescence band and a larger Stokes-shift compared to the unsubstituted species. These effects are in most cases less pronounced for the beta-substituted structures. In particular, we found that the Stokes-shift of the alpha-substituted structures is larger than the one of the beta-substituted species due to a more planar orientation of the methylsulfanyl group with respect to the neighbouring thiophene in the excited state.     

Do computed crystal structures of nonpolar molecules depend on the electrostatic interactions? The case of tetracene

We present a strategy for comparing the global properties of competing potential models. By systematically sampling the potential energy surface of crystalline tetracene, we assess how the number, energy and structure of its minima are modified by switching on (or off) the Coulombic interactions. The increased complexity of the Coulombic potential leads to a more "rugged" potential energy surface with a larger number of minima, but the effect is not large. In fact, we find a subset of minima stable only in presence of the Coulombic interactions, a smaller subset stable only in their absence, and a large majority stable in both cases. Among these, there is a very good, but not perfect, correlation between the energies and the structures computed with and without the electrostatic interactions. Although electrostatic interactions play a role even in a rigid nonpolar molecule such as tetracene, they are not as crucial as often believed, because altering the electrostatic model (or switching it off completely) leads, in most cases, to equivalent results.     

He I photoelectron spectra and valence synchrotron photoionization for XC(O)SCl (X = F, Cl) compounds

Small penta-atomic molecules like FC(O)SCl and ClC(O)SCl have been analyzed by using both photoelectron spectroscopy (PES) and results derived from the use of synchrotron radiation in the same energy range. For this second experiment total ion yield (TIY), photoelectron photoion coincidence (PEPICO), and partial ion yield (PIY) spectra have been recorded. This set of data together with results obtained by computational chemistry allow us to study electronic properties and the ionization channels of both species. Thus, whereas the photodissociation behavior of FC(O)SCl can be divided into three well-defined energy regions, the fragmentation dynamics of ClC(O)SCl seems to be more complex. Nevertheless, simultaneous evaluation of the PES and valence synchrotron photoionization studies helps to clarify the molecular ionization processes.     

Car-Parrinello MD simulations for the Na+ -phenylalanine complex in aqueous solution

Car-Parrinello molecular dynamics (CPMD) calculations are presented for a Na (+)(Phe) complex in aqueous solution and for various stable Na (+)(Phe) complexes and Na (+)(H 2O) n clusters in the gas phase (with up to six water molecules). The CPMD results are compared to available experimental and ab initio reference data, to DFT results obtained with various combinations of density functionals and basis sets, and to previous classical mechanics MD simulations. The agreement with the reference data in the gas phase validates the CPMD method, showing that it is a valid approach for studying these systems and that it describes correctly the competing Na (+)-Phe and Na (+)-H 2O interactions. Analysis of MD trajectories reveals that the Na (+)(Phe) complex in aqueous solution maintains a stable configuration in which the Na (+) cation hovers above the phenyl ring, at an average distance of 3.85 A from the ring center, while remaining strongly bound to one of the carboxylic oxygens of Phe. Constrained MD simulations indicate that the free energy barrier opposing dissociation of the complex exceeds 5.5 kcal/mol. We thus confirm that "cation- pi" interactions between alcali cations and the pi ring, combined with other kinds of interactions, may allow aromatic amino acids to overcome the competition with water in binding a cation.     

Multiconfiguration optimized effective potential method for a density-functional treatment of static correlation

An approach to treat static correlation within a density-functional framework is presented. To that end, a multiconfiguration optimized effective potential (MCOEP) method is derived. In contrast to standard multiconfiguration self-consistent field (MCSCF) methods and previous combinations of MCSCF procedures with density-functional theory, the MCOEP method yields well-defined physically meaningful orbital and eigenvalue spectra. In addition to the electronic ground state also excited electronic states can be described. The MCOEP method is implemented invoking the localized Hartree-Fock approximation, leading to a multiconfiguration localized Hartree-Fock approach. Applications of the new method to the dissociation of the hydrogen molecule and the isomerization of ethene and cyclobutadiene show that it is capable of describing situations that are characterized by strong static correlation.     

Industrial Applications of Gold Catalysis

Gold catalysis has recently found its first large‐scale applications in the chemical industry. This Minireview provides a critical analysis of the success factors and of the main obstacles that had to be overcome on the long way from the discovery to the commercialization of gold catalysts. The insights should be useful to researchers in both academia and industry working on the development of tomorrow's gold catalysts to tackle significant environmental and economic issues.     

Accurate Kohn–Sham ionization potentials from scaled‐opposite‐spin second‐order optimized effective potential methods

One important property of Kohn–Sham (KS) density functional theory is the exact equality of the energy of the highest occupied KS orbital (HOMO) with the negative ionization potential of the system. This exact feature is out of reach for standard density‐dependent semilocal functionals. Conversely, accurate results can be obtained using orbital‐dependent functionals in the optimized effective potential (OEP) approach. In this article, we investigate the performance, in this context, of some advanced OEP methods, with special emphasis on the recently proposed scaled‐opposite‐spin OEP functional. Moreover, we analyze the impact of the so‐called HOMO condition on the final quality of the HOMO energy. Results are compared to reference data obtained at the CCSD(T) level of theory. © 2016 Wiley Periodicals, Inc.     

A saturation phenomenon for a nonlinear nonlocal eigenvalue problem

Given \(1\le q \le 2\) and \(\alpha \in \mathbb {R}\), we study the properties of the solutions of the minimum problem

$$\begin{aligned} \lambda (\alpha ,q)=\min \left\{ \dfrac{\displaystyle \int _{-1}^{1}|u'|^{2}dx+\alpha \left| \int _{-1}^{1}|u|^{q-1}u\, dx\right| ^{\frac{2}{q}}}{\displaystyle \int _{-1}^{1}|u|^{2}dx}, u\in H_{0}^{1}(-1,1),\,u\not \equiv 0\right\} . \end{aligned}$$

In particular, depending on \(\alpha \) and q, we show that the minimizers have constant sign up to a critical value of \(\alpha =\alpha _{q}\), and when \(\alpha >\alpha _{q}\) the minimizers are odd.

     

From glycerol to value-added products

Today, industrial plants that produce glycerol are closing down and others are opening that use glycerol as a raw material, owing to the large surplus of glycerol formed as a by-product during the production of biodiesel. Research efforts to find new applications of glycerol as a low-cost feedstock for functional derivatives have led to the introduction of a number of selective processes for converting glycerol into commercially valued products. This Minireview describes a selection of such achievements and shows how glycerol will be a central raw material in future chemical industries.     

Imaging photoelectron transmission through self-assembled monolayers: the work-function of alkanethiols coated gold

In this paper, we present a new approach for studying the electronic properties of self-assembled monolayers and their interaction with a conductive substrate, the low-energy photoelectron imaging spectroscopy (LEPIS). LEPIS relies on imaging of photoelectrons ejected from a conductive substrate and subsequently transmitted through organic monolayers. Using this method, we measure the relative work-function of alkanethiols of different length on gold substrate, and we are able to follow the changes occurring when the surface coverage is varied. We also computed the work-function of model alkanethiols using a plane-wave density functional theory approach, in order to demonstrate the correlation between changes in the work-function with the monolayer organization and density.