Solvent Effects in Organic Spectra: Dipole Forces and the Franck–Condon Principle

Abstract

All organic electronic spectra in solution are subject to a generalized polarization red shift which is due to solvent polarization by the transition dipole and which depends on the solvent refractive index. This can be obscured by the effect of dipole-dipole and dipole-polarization forces if the solute is polar, when the application of the Franck-Condon principle shows that the solvent cage around the excited solute molecule is momentarily strained. Orientation strain ana packing strain are defined, of which the former is more important. The absorption frequencies of polar solutes are shifted to the red in solution if the dipole moment increases during the transition; they may be shifted to the blue (relative to the gas) if the dipole moment decreases. Four cases are discussed according to whether solute and solvent are polar or non-polar. The place of ir* *n transitions is discussed.

Implementation of the analytic energy gradient for the combined time-dependent density functional theory/effective fragment potential method: Application to excited-state molecular dynamics simulations

“…In the following discussion, the transition energies in the fourth column in Table III are employed. The excitation energy difference between the gas and solution phases, the solvatochromic shift, is calculated to be 0.34 eV, which is comparable to the experimental value of 0.21 eV for acetone 56 as well as to previous theoretical results. 20,[34][35][36][37][38][39][40][41][42] …”

Fundamental Studies and Applications of Supercritical Fluids

“…For example, Okada et al (29) and Kajimoto and co-workers (30) studied intramolecular excited-state complexation (exciplex) and charge-transfer formation, respectively, in supercritical CHF 3 . In the latter studies, the observed spectral shift was more than expected based on the McRae theory (56,57), this was attributed to cluster formation. In other studies, Brennecke and Eckert (5,31,44,45) examined the fluorescence of pyrene in supercritical CQ2, C 2 H^y and CHF 3 .…”

“…For all fluids, spectral shifts were observed with fluid density. Yonker, Smith and co-workers (24-26,28) compared their results to the McRae continuum model for dipolar solvation (56,57), which is based on Onsanger reaction field theory (58). Over a limited density range, there was agreement between the experimental data and the model (24)(25)(26)28), but conditions existed where the predicted linear relationship was not followed (28).…”

“…Local densities were recovered by comparison of the observed spectral shift (or position) to that expected for a homogeneous polarizable dielectric medium. Clustering manifests itself in deviation from the expected linear McRae continuum model (17,18,20,27,32,56,57). These data were subsequently interpreted using an expression derived from Kirkwood-Buff solution theory (20).…”

Solvent Induced Shifts in the UV Spectrum of Amides

“…Overall, a blue-shift was predicted for the n−π* state and red-shift was predicted for the π nb −π* state of HCONH 2 (H 2 O) 16 , with respect to HCONH 2 . The mean values for the n−π* and π nb −π* excitation energies of HCONH 2 (H 2 O) 16 are blue-and redshifted by +0.52 and −0.33 eV, respectively, compared to the gas phase at 300 K. The authors also noted that structural changes in the amides contribute to the π nb −π* red-shift.…”