Brenlla, AlfonsoVeiga Gutiérrez, ManoelRíos Rodríguez, María del CarmenRodríguez-Prieto, FlorMosquera González, ManuelPérez Lustres, José Luis2018-07-182018-07-182014Brenlla, A., Veiga Gutiérrez, M., Ríos Rodríguez, M., Rodríguez-Prieto, F., Mosquera, M., & Pérez Lustres, J. (2014). Moderately Strong Photoacid Dissociates in Alcohols with High Transient Concentration of the Proton-Transfer Contact Pair. The Journal Of Physical Chemistry Letters, 5(6), 989-994. doi: 10.1021/jz5001648http://hdl.handle.net/10347/17051This is the peer-reviewed version of the following article: The Journal of Physical Chemistry Letters 2014, 5, 989–994, DOI: 10.1021/jz5001648, which has been published in final form at https://pubs.acs.org/doi/abs/10.1021/jz5001648. This article may be used for non-commercial purposes onlyProton transfer from strong photoacids to hydroxylic solvents is much under debate. Experimentally, the main issue stems from relaxation and diffusion processes that are concomitant with ultrafast proton transfer and blur population dynamics. To overcome this, we propose a fast photodissociation reaction that, however, proceeds slower than solvent relaxation. Fluorescence spectroscopy of the cationic photoacid 2-(1′-hydroxy-2′-naphtyl)benzimidazolium reveals a two-stage mechanism: (a) reversible elementary proton transfer inside the solvent shell and (b) irreversible contact-pair splitting. The time evolution of the fluorescence signal is complex, yet this is explained quantitatively by simultaneous, spectrally overlapping emission of the acid, the conjugate base, and the contact proton-transfer pair. The latter attains high transient concentration in linear alcohols. Microscopic rate constants of dissociation are determinedeng© 2014 American Chemical SocietyAcids and basesFluorescence spectroscopyKinetics and photochemistryProton transferSolution chemistryTime-resolved spectroscopyjournal article10.1021/jz50016481948-7185open access