title: Ultrafast excited-state proton transfer to the solvent occurs on a hundred-femtosecond time-scale.
abstract: Steady-state and ultrafast time-resolved techniques were used to study a newly synthesized photoacid, phenol-carboxyether dipicolinium cyanine dye, QCy9. We found that the excited-state proton transfer (ESPT) to water occurs at the remarkably short time of about 100 fs, k(PT) ≈ 1 × 10(13) s(-1), the fastest rate reported up to now. On the basis of the Förster-cycle, the pK(a)* value is estimated to be -8.5 ± 0.4. In previous studies, we reported the photoacidity of another superphotoacid, the QCy7 for which we found an ESPT rate constant of ~1.25 × 10(12) s(-1), one-eighth that of the QCy9 compound. We found a kinetic isotope effect of the ESPT of about two.
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: Naama
authors.initials: N
authors.lastname: Karton-Lifshin
authors.forename: Shay
authors.initials: S
authors.lastname: Shomer
authors.forename: Doron
authors.initials: D
authors.lastname: Shabat
authors.forename: Dan
authors.initials: D
authors.lastname: Huppert