Comprehensive study of ultrafast excited-state proton transfer in water and D2O providing the missing RO-⋯H+ ion-pair fingerprint

Ron Simkovitch, Katherine Akulov, Shay Shomer, Michal E. Roth, Doron Shabat, Tal Schwartz, Dan Huppert

Research output: Contribution to journalArticlepeer-review

Abstract

Steady-state and time-resolved optical techniques were employed to study the photoprotolytic mechanism of a general photoacid. Previously, a general scheme was suggested that includes an intermediate product that, up until now, had not been clearly observed experimentally. For our study, we used quinone cyanine 7 (QCy7) and QCy9, the strongest photoacids synthesized so far, to look for the missing intermediate product of an excited-state proton transfer to the solvent. Low-temperature steady-state emission spectra of both QCy7 and QCy9 clearly show an emission band at T < 165 K in H2O ice that could be assigned to ion-pair RO-*⋯H3O+, the missing intermediate. Room-temperature femtosecond pump-probe spectroscopy transient spectra at short times (t < 4 ps) also shows the existence of transient absorption and emission bands that we assigned to the RO -*⋯H3O+ ion pair. The intermediate dissociates on a time scale of 1 ps and about 1.5 ps in H2O and D2O samples, respectively.

Original languageEnglish
Pages (from-to)4425-4443
Number of pages19
JournalJournal of Physical Chemistry A
Volume118
Issue number25
DOIs
StatePublished - 26 Jun 2014

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