Computational study on intramolecular electron transfer in 1,3-dintrobenzene radical anion

Abstract

1,3‐Dinitrobenzene radical anion (DNB−), which is a typical mixed valence compound, undergoes intramolecular electron transfer (ET) in solution. It is reported that the ET rates exceed 1010 s−1 in polar aprotic solvent such as acetonitrile. Formulation based on a simple one‐dimensional model cannot quantitatively account for the observed ET rates, and further study has been desired for better understanding of the solvent effects on the ET. In the present study, molecular dynamics simulations were performed for DNB− in the vacuum and in acetonitrile solution. In the vacuum, ET was induced by the antisymmetric C–N stretching mode on a timescale of ~100 fs, and the charge transferring between the nitro groups was much less than unity. For the acetonitrile solution, short‐timescale and long‐timescale simulations were performed using a droplet model of solvated DNB− at 298 K. Although the mean C–N distance in the charged nitro group was longer than that in the vacuum, no ET took place in the short (~150 fs) simulations. The solvent coordinate, which was defined as the difference in the solute–solvent interaction energy between the reactant and the product, significantly fluctuated even in short‐time simulations. The reorganization energies in acetonitrile were evaluated on the basis of molecular orbital (MO) calculations, and the ratio of the inner sphere and outer sphere parts, λi/λo, was estimated to be ~0.6. The results suggest that the intramolecular mode and fast solvent mode may play an important role in the present ET reaction. Copyright © 2014 John Wiley & Sons, Ltd.

MVO-10: A Gas-Phase Oxide Benchmark for Localization/Delocalization in Mixed-Valence Systems

“…Moreover, many of the MV systems of chemical or technological interest may have appreciable size, rendering the most accurate post-Hartree–Fock methodologies to treat point (a) too computationally demanding at present. Our own efforts in the field, and those of many others (see literature provided in ref ), have thus focused on using suitably chosen density-functional theory (DFT) approaches, combined with solvent models ranging from dielectric continuum models, via more advanced implicit solvent models like the D-COSMO-RS approach , or methods based on the reactive interaction site model (RISM), to explicit QM/MM molecular dynamics simulations . An evaluation of the electronic-structure method becomes of course more complicated when the solvent model may introduce specific errors into the computations.…”

“…Our own efforts in the field, and those of many others (see literature provided in ref 2), have thus focused on using suitably chosen density-functional theory (DFT) approaches, combined with solvent models ranging from dielectric continuum models, via more advanced implicit solvent models like the D-COSMO-RS approach 5,6 or methods based on the reactive interaction site model (RISM), 7 to explicit QM/MM molecular dynamics simulations. 8 An evaluation of the electronic-structure method becomes of course more complicated when the solvent model may introduce specific errors into the computations. It is thus desirable to find suitable gas-phase MV systems, on both sides of the Robin/Day classification, to validate the quantumchemical methods in the absence of environmental effects.…”

[Al2O4]−, a Benchmark Gas-Phase Class II Mixed-Valence Radical Anion for the Evaluation of Quantum-Chemical Methods

“…However, in view of the above-mentioned complications arising from the treatment of environmental effects, the possibility of fortuitous error compensation cannot be ruled out completely. Other approaches to the electronic structure-problem (e.g., tuned range hybrids) or to the treatment of environmental effects (e.g., QM/MM molecular dynamics approaches or the RISM-SCF model) have been put forward. We note also, that some previous method evaluations have compared gas-phase calculations to condensed-phase experimental data which are expected to be heavily influenced by the environment or to ab initio benchmark data that may not have been converged sufficiently in terms of one-particle basis sets …”

Identifying the Marcus dimension of electron transfer from ab initio calculations

“…Approaches to identify the ET dimension based on a statistical ensemble (like molecular dynamics) are either missing or do not focus on the interplay between electronic and geometric structure. 44 In state-of-the-art theoretical research of MV systems, a unified strategy towards a coordinate that describes electron transfer (Class II) or localisation (Class III) and that can be used to disentangle intra-molecular motion from solvent motion is missing.…”