Effect of Solvent on n-π^* Absorption Spectra of Ketones

Unusual photobehavior of benzophenone triplets in hexafluoroisopropanol. Inversion of the triplet character of benzophenone

“…This red shift of the → * band amounts to as much as 12 nm in HFIP with respect to ACN, corresponding to a stabilization of the singlet , * state relative to the ground state by 22.0 kJ mol −1 . These data are in accord with previous findings [16][17][18][19] where the most important contribution to the observed solvatochromism was attributed to the effect of specific solute-solvent interactions resulting from the formation of hydrogen bonding between the solute molecule and the protic solvent.…”

Efficient Photochemical Oxidation of Anisole in Protic Solvents: Electron Transfer driven by Specific Solvent–Solute Interactions

“…These conclusions are fully in accord with early studies of the BP solvation, which referred the spectral red-shift of the p!p* absorption to (relatively weaker) effects of the permittivity and (relatively stronger) effects of the HB to the solvent; that is, to unspecific and specific solvation, respectively. [23][24][25] In order to characterize the hydrogen bonding of solvent molecules with benzophenone in a quantitative manner, the equilibrium constants K, for the formation of 1:1 hydrogen bonded solvent-solute complexes were extracted from the spectral effects of protic additives to BP solutions in dichloromethane (DCM) on the n!p* band of BP around 340 nm. Absorption spectra of BP in dilute DCM solution were measured in the presence of varying amounts of TFE ( Figure 1) and HFIP, exhibiting the typical blue shift of an n!p* absorption band in HB media.…”

Two-response-time model based on CM2/INDO/S2 electrostatic potentials for the dielectric polarization component of solvatochromic shifts on vertical excitation energies

“…There is experimental evidence in many cases that the major part of the solvatochromic shifts for non‐hydrogen‐bonding polar solvents are usefully modeled by the interaction of the permanent and average induced charge distribution of the solute with a polarizable medium 8–16. Quantitative treatments must take account of the fact that the electronic part of the electric polarization of the solvent readjusts instantaneously to solute electronic excitation whereas the part of the solvent's electric polarization requiring solvent nuclear motions (typically described as reorientational but also including translation and internal vibration) responds orders of magnitude more slowly 8–10, 12–16. It is possible that one can account for part of the hydrogen‐bonding effect by treating one or more associated solvent molecules as part of the solute, and, if the level of theory used for the solute is high enough and if one can average over the solvent orientations well enough (which may pose more of a challenge for many weak interactions than for one or two strong hydrogen bonds), one might also be able to account in this way for changes in dispersion and exchange–repulsion upon electronic excitation.…”