title: Comprehensive study of ultrafast excited-state proton transfer in water and D2O providing the missing RO(-)···H(+) ion-pair fingerprint.
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.
authors.affiliation: Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University , Tel Aviv 69978, Israel.
authors.forename: Ron
authors.initials: R
authors.lastname: Simkovitch
authors.forename: Katherine
authors.initials: K
authors.lastname: Akulov
authors.forename: Shay
authors.initials: S
authors.lastname: Shomer
authors.forename: Michal E
authors.initials: ME
authors.lastname: Roth
authors.forename: Doron
authors.initials: D
authors.lastname: Shabat
authors.forename: Tal
authors.initials: T
authors.lastname: Schwartz
authors.forename: Dan
authors.initials: D
authors.lastname: Huppert