title: Tautomerism in porphycenes: analysis of rate-affecting factors.
abstract: Double hydrogen transfer occurring in both ground and the lowest electronically excited singlet states was studied for a series of 19 differently substituted porphycenes. The rates of tautomerization have been determined using femtosecond pump-probe spectroscopy with polarized light. The values vary by over 3 orders of magnitude, suggesting the importance of tunneling. Good correlation exists between the values of the rates and the parameters characterizing the strength of two intramolecular hydrogen bonds: proton NMR shift, distance between the hydrogen-bonded nitrogen atoms, and the NH stretching frequency. While hydrogen-bond strength is the main factor determining the rate of double hydrogen transfer, other factors, such as static and dynamic symmetry breaking and the population of low-frequency vibrations also have to be taken into account.
authors.affiliation: Institute of Experimental Physics, Faculty of Physics, University of Warsaw , Hoża 69, 00-681 Warsaw, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Ciąćka
authors.forename: Piotr
authors.initials: P
authors.lastname: Fita
authors.forename: Arkadiusz
authors.initials: A
authors.lastname: Listkowski
authors.forename: Michał
authors.initials: M
authors.lastname: Kijak
authors.forename: Santi
authors.initials: S
authors.lastname: Nonell
authors.forename: Daiki
authors.initials: D
authors.lastname: Kuzuhara
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamada
authors.forename: Czesław
authors.initials: C
authors.lastname: Radzewicz
authors.forename: Jacek
authors.initials: J
authors.lastname: Waluk