Exploring single and double proton transfer processes in the gas phase: A high resolution electronic spectroscopy study of 5-fluorosalicylic acid

Abstract

Two species that possess different absorption and emission properties have been observed in the low resolution fluorescence excitation spectrum of 5-fluorosalicylic acid (FSA) in the gas phase. The two species were identified as monomer and dimer species using high resolution techniques. Studies of these spectra in the presence of an applied electric field, together with ab initio quantum chemistry calculations, show that the monomer is a "closed" form of FSA exhibiting an intramolecular C = O⋅⋅⋅H-O-C hydrogen bond in the ground state. Absorption of light at ∼344 nm transforms this species into the tautomeric form C-O-H⋅⋅⋅O = C via a barrierless proton transfer process. The large charge rearrangement that accompanies this process results in a significantly red-shifted emission spectrum. The (FSA)(2) dimer exhibits two intermolecular C=O⋯H-O-C hydrogen bonds but in this case the double proton transfer leads to a conical intersection with the ground state and rapid nonradiative decay. The onset of this process and the time scale on which it occurs are revealed by a homogeneous broadening of the dimer's high resolution spectrum.

Excited Electronic State Mixing in 7-Azaindole. Quantitative Measurements Using the Stark Effect

“…Parenthetically, we remark at this juncture that one might expect significantly broadened LIF spectra in systems undergoing photoinduced proton transfer and/or other tautomerization processes in the gas phase. Indeed, such a behavior has been observed by us in several systems, and used to determine the time scales of such processes. , However, even in cases where broadening of this type is not observed, owing to higher barriers along a reaction coordinate, a rotationally resolved spectrum can still, in principle, contain information about possible dynamical behaviors following Franck–Condon (FC) absorption, since rotations are slow with respect to vibrational motion and are sensitive to changes in the potential energy surface beyond the FC region. Examples of this type of behavior may be found in our recent studies of the electronically excited states of charge-transfer systems, , in which significant photoinduced changes in electronic distributions were observed.…”

Correlation between Excited-State Intramolecular Proton-Transfer and Singlet-Oxygen Quenching Activities in 1-(Acylamino)anthraquinones

“…In this paper, the ESIPT activity depending on the relative energies of the S 1 (T) and S 1 (N) states in AYAAQs is explained in terms of the nodal-plane model, , which is a qualitative theoretical model but allows us to recognize important features of the ESIPT immediately. Many chemists have cited the nodal-plane model, and recognized usefulness of the explanation even in quite recent years. ,− Furthermore, the positive and linear relationship between the ESIPT and 1 O 2 quenching activities in AYAAQs is interpreted on the basis of ESIPT-induced distortion of their S 0 -state potential surface and their encounter complex formation with 1 O 2 .…”

Excited-State Proton Transfer in syn-2-(2′-Pyridyl)pyrrole Occurs on the Nanosecond Time Scale in the Gas Phase

“…The same is true for 7AI–H 2 O . Solvent molecules are not required in the salicylic acid/MS systems, since the dipoles of the two connecting states are more nearly aligned, and there is no barrier, even in the isolated molecule . Therefore, it is perhaps not surprising that the ESPT reaction of 2PP in the gas phase is significantly slower than the corresponding reaction in solution.…”