Solvation and Protonation of Coumarin 102 in Aqueous Media - a Fluorescence Spectroscopic and Theoretical Study

The ground and excited state protonation of Coumarin 102 (C102), a fluorescent probe applied frequently in heterogeneous systems with an aqueous phase, has been studied in aqueous solutions by spectroscopic experiments and theoretical calculations. For the dissociation constant of the protonated form in the ground state, was obtained from the absorption spectra, for the excited state dissociation constant was obtained from the fluorescence spectra. These values were closely reproduced by theoretical calculations via a thermodynamic cycle – the value of also by calculations via the Förster cycle - using an implicit-explicit solvation model (polarized continuum model + addition of a solvent molecule). The theoretical calculations indicated that (i) in the ground state C102 occurs primarily as a hydrogen bonded water complex, with the oxo group as the binding site, (ii) this hydrogen bond becomes stronger upon excitation; (iii) in the ground state the amino nitrogen atom, in the excited state the carboxy oxygen atom is the protonation site. A comprehensive analysis of fluorescence decay data yielded the values kpr = 3.271010 M-1 s 1 for the rate constants of excited state protonation, and kdpr = 2.78108 s-1 for the rate constant of the reverse process (kpr and kdpr were treated as independent parameters). This, considering the relatively long fluorescence lifetimes of neutral C102 (6.02 ns) and its protonated form (3.06 ns) in aqueous media, means that a quasi-equilibrium state of excited state proton transfer is reached in strongly acidic solutions

New Strategies in Modeling Electronic Structures and Properties with Applications to Actinides

This chapter discusses contemporary quantum chemical methods and provides general insights into modern electronic structure theory with a focus on heavy-element-containing compounds. We first give a short overview of relativistic Hamiltonians that are frequently applied to account for relativistic effects. Then, we scrutinize various quantum chemistry methods that approximate the $N$-electron wave function. In this respect, we will review the most popular single- and multi-reference approaches that have been developed to model the multi-reference nature of heavy element compounds and their ground- and excited-state electronic structures. Specifically, we introduce various flavors of post-Hartree--Fock methods and optimization schemes like the complete active space self-consistent field method, the configuration interaction approach, the Fock-space coupled cluster model, the pair-coupled cluster doubles ansatz, also known as the antisymmetric product of 1 reference orbital geminal, and the density matrix renormalization group algorithm. Furthermore, we will illustrate how concepts of quantum information theory provide us with a qualitative understanding of complex electronic structures using the picture of interacting orbitals. While modern quantum chemistry facilitates a quantitative description of atoms and molecules as well as their properties, concepts of quantum information theory offer new strategies for a qualitative interpretation that can shed new light onto the chemistry of complex molecular compounds.Comment: 43 pages, 3 figures, Version of Recor

Projected atomic orbitals as optimal virtual space for excited state projection-based embedding calculations

The projected atomic orbitals (PAO) technique is presented for the construction of virtual orbital spaces in projection-based embedding (PbE) applications. The proposed straightforward procedure produces a set of virtual orbitals, which is used in the final, high-level calculation of the embedded active subsystem. The PAO scheme is demonstrated on intermolecular potentials of bimolecular complexes, in ground and excited states, including Rydberg excitations. The results show the outstanding performance of the PbE method when used with PAO virtual orbitals compared to those produced using common orbital localization techniques. The good agreement of the resulting PbE potential curves with those from high-level \ai dimer calculations, also in diffuse basis sets, confirms that the PAO technique can be suggested for future applications using top-down embedding methods

Optimization of the linear-scaling local natural orbital CCSD(T) method: improved algorithm and benchmark applications

An optimized implementation of the local natural orbital (LNO) coupled-cluster (CC) with single-, double-, and perturbative triple excitations [LNO–CCSD­(T)] method is presented. The integral-direct, in-core, highly efficient domain construction technique of our local second-order Møller–Plesset (LMP2) scheme is extended to the CC level. The resulting scheme, which is also suitable for general-order LNO–CC calculations, inherits the beneficial properties of the LMP2 approach, such as the asymptotically linear-scaling operation count, the asymptotically constant data storage requirement, and the completely independent domain calculations. In addition to integrating our recent redundancy-free LMP2 and Laplace-transformed (T) algorithms with the LNO–CCSD­(T) code, the memory demand, the domain and LNO construction, the auxiliary basis compression, and the previously rate-determining two-external integral transformation have been significantly improved. The accuracy of all of the approximations is carefully examined on medium-sized to large systems to determine reasonably tight default truncation thresholds. Our benchmark calculations, performed on molecules of up to 63 atoms, show that the optimized method with the default settings provides average correlation and reaction energy errors of less than 0.07% and 0.34 kcal/mol, respectively, compared to the canonical CCSD­(T) reference. The efficiency of the present LNO–CCSD­(T) implementation is demonstrated on realistic, three-dimensional examples. Using the new code, an LNO–CCSD­(T) correlation energy calculation with a triple-ζ basis set is feasible on a single processor for a protein molecule including 2380 atoms and more than 44000 atomic orbitals