Solvent dependence of Stokes shift for organic solute–solvent systems: A comparative study by spectroscopy and reference interaction-site model–self-consistent-field theory

Abstract

The Stokes shift magnitudes for coumarin 153 (C153) in 13 organic solvents with various polarities have been determined by means of steady-state spectroscopy and reference interaction-site model-self-consistent-field (RISM-SCF) theory. RISM-SCF calculations have reproduced experimental results fairly well, including individual solvent characteristics. It is empirically known that in some solvents, larger Stokes shift magnitudes are detected than anticipated on the basis of the solvent relative permittivity, ɛr. In practice, 1,4-dioxane (ɛr = 2.21) provides almost identical Stokes shift magnitudes to that of tetrahydrofuran (THF, ɛr = 7.58), for C153 and other typical organic solutes. In this work, RISM-SCF theory has been used to estimate the energetics of C153-solvent systems involved in the absorption and fluorescence processes. The Stokes shift magnitudes estimated by RISM-SCF theory are ∼5 kJ mol(-1) (400 cm(-1)) less than those determined by spectroscopy; however, the results obtained are still adequate for dipole moment comparisons, in a qualitative sense. We have also calculated the solute-solvent site-site radial distributions by this theory. It is shown that solvation structures with respect to the C-O-C framework, which is common to dioxane and THF, in the near vicinity (∼0.4 nm) of specific solute sites can largely account for their similar Stokes shift magnitudes. In previous works, such solute-solvent short-range interactions have been explained in terms of the higher-order multipole moments of the solvents. Our present study shows that along with the short-range interactions that contribute most significantly to the energetics, long-range electrostatic interactions are also important. Such long-range interactions are effective up to 2 nm from the solute site, as in the case of a typical polar solvent, acetonitrile.

Solvation Dynamics in Liquid Water. 1. Ultrafast Energy Fluxes

“…The case of a diatomic undergoing a change of dipole moment could prove a particularly natural choice (and one reflective of a less concentrated charge redistribution), but we consider that this methodology should also be adequate and specially useful for the challenge of increasing levels of complexity where a molecular perspective has been particularly difficult to achieve 18,19,84,85 . But before addressing these issues, we first intend to report in this series on some aspects that have been left untouched for the simple solute problem addressed here.…”

Evaluation of an Efficient 3D-RISM-SCF Implementation as a Tool for Computational Spectroscopy in Solution

“…We evaluate the new implementation in TDDFT calculations for several examples in the field of solvatochromism and show its efficiency and applicability to large systems. This is an area where different RISM versions such as RISM-SCF, , RISM-SCF-SEDD, − and 3D-RISM , have been evaluated in many previous works. Our emphasis will be on the systematic comparison of a variety of different solvents.…”

Relation between Anharmonicity of Free-Energy Profile and Spectroscopy in Solvation Dynamics: Differences in Spectral Broadening and Peak Shift in Transient Hole-Burning Spectroscopy Studied by Equilibrium Molecular Dynamics Simulation

“…For instance, solvation probes where a carbonyl moiety is introduced to an oxazine ring are sometimes used. A dominant dipole-moment change occurs around the CO moiety upon photo-excitation, , which brings about significant solvent rearrangements in close proximity to the moiety . Dynamics driven by anharmonicity is also essentially attributed to that region .…”

“…A dominant dipole-moment change occurs around the CO moiety upon photo-excitation, 26,28 which brings about significant solvent rearrangements in close proximity to the moiety. 28 Dynamics driven by anharmonicity is also essentially attributed to that region. 26 On the other hand, a system in which many solvents take part in the relaxation may demonstrate a Gaussian process due to the central limit theorem.…”