RT Journal Article
T1 Dissociation of a Strong Acid in Neat Solvents: Diffusion Is Observed after Reversible Proton Ejection Inside the Solvent Shell
A1 Veiga Gutiérrez, Manoel
A1 Brenlla, Alfonso
A1 Carreira Blanco, Carlos
A1 Fernández Rodríguez, Berta
A1 Kovalenko, Sergey A.
A1 Rodríguez-Prieto, Flor
A1 Mosquera González, Manuel
A1 Pérez Lustres, José Luis
AB Strong-acid dissociation was studied in alcohols. Optical excitation of the cationic photoacid N-methyl-6-hydroxyquinolinium triggers proton transfer to the solvent, which was probed by spectral reconstruction of picosecond fluorescence traces. The process fulfills the classical Eigen–Weller mechanism in two stages: (a) solvent-controlled reversible dissociation inside the solvent shell and (b) barrierless splitting of the encounter complex. This can be appreciated only when fluorescence band integrals are used to monitor the time evolution of the reactant and product concentrations. Band integrals are insensitive to solvent dynamics and report relative concentrations directly. This was demonstrated by first measuring the fluorescence decay of the conjugate base across the full emission band, independently of the proton-transfer reaction. Multiexponential decay curves at single wavelengths result from a dynamic red shift of fluorescence in the course of solvent relaxation, whereas clean single exponential decays are obtained if the band integral is monitored instead. The extent of the shift is consistent with previously reported femtosecond transient absorption measurements, continuum theory of solvatochromism, and molecular properties derived from quantum chemical calculations. In turn, band integrals show clean biexponential decay of the photoacid and triexponential evolution of the conjugate base in the course of the proton transfer to solvent reaction. The dissociation step follows the slowest stage of solvation, which was measured here independently by picosecond fluorescence spectroscopy in five aliphatic alcohols. Also, the rate constant of the encounter-complex splitting stage is compatible with proton diffusion. Thus, for this photoacid, both stages reach the highest possible rates: solvation and diffusion control. Under these conditions, the concentration of the encounter complex is substantial during the earliest nanosecond
PB American Chemical Society
SN 1520-6106
YR 2013
FD 2013
LK http://hdl.handle.net/10347/17050
UL http://hdl.handle.net/10347/17050
LA eng
NO Veiga-Gutiérrez, M., Brenlla, A., Carreira Blanco, C., Fernández, B., Kovalenko, S., & Rodríguez-Prieto, F. et al. (2013). Dissociation of a Strong Acid in Neat Solvents: Diffusion Is Observed after Reversible Proton Ejection Inside the Solvent Shell. The Journal Of Physical Chemistry B, 117(45), 14065-14078. doi: 10.1021/jp4042765
NO This is the peer-reviewed version of the following article:The Journal of Physical Chemistry B 2013, 117, 14065–14078, DOI: 10.1021/jp4042765, which has been published in final form at https://pubs.acs.org/doi/abs/10.1021/jp4042765.This article may be used for non-commercial purposes only
NO We thank the Spanish Government and the European Regional Development Fund (grant nos. CTQ2010-17835, CTQ2010-17026, and CTQ2011-29311-C02-01) and the Xunta de Galicia (grants nos. CN 2012/314, 2012-PG237, GPC2013/052 and INCITE09 314 252 PR) for financial support of our work. J.L.P.L. thanks the Spanish Ministry of Economy and Competitiveness for funding through the Ramon y Cajal ́Programm 2009. M.V. and C.C.B. thank the Spanish Government for funding through the FPU program. A. B. thanks the Segundo Gil Dávila Foundation for financial support
DS Minerva
RD 24 abr 2026