title: Solvent control of intramolecular proton transfer: is 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde a proton crane?
abstract: The solvent dependent excited state dynamics of 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde (compound 2), a candidate for a molecular switch based on intramolecular proton transfer, was investigated by ultrafast spectroscopy and quantum-chemical calculations. In acetonitrile a mixture of molecules in the enol and zwitterionic proton transfer (PT) form exists in the ground state. However, the zwitterion is the energetically favored one in the electronically excited state. Optical excitation of the enol form results in intramolecular proton transfer and formation of the PT form within 1.4 ps. In addition we observe the appearance of a long living species with a rate of 1/(330 ps) which returns to the original ground state on time scales beyond 2 ns and which is attributed to the triplet state. In toluene the enol form is the only observed ground state tautomer, but no light induced proton transfer occurs. Again the long living triplet state is formed, even with a faster rate of 1/(11 ps). In methanol hydrogen bonds between 2 and solvent molecules stabilize strongly the PT form in the ground as well as in the excited state. Also in this case no light induced intramolecular proton transfer was observed but the formation of a long living species was. However, its absorption spectrum is distinctly different from the triplet state seen in acetonitrile and methanol.
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G.Bonchev str., bldg. 9, 1113 Sofia, Bulgaria. lantonov@orgchm.bas.bg.
authors.forename: Y
authors.initials: Y
authors.lastname: Manolova
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Straße 23-24, 18059 Rostock, Germany and Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Marciniak
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Straße 23-24, 18059 Rostock, Germany and Institute of Inorganic Chemistry 1, University Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: S
authors.identifier: http://orcid.org/0000-0001-9441-7904
authors.initials: S
authors.lastname: Tschierlei
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Straße 23-24, 18059 Rostock, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Fennel
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: F S
authors.initials: FS
authors.lastname: Kamounah
authors.affiliation: Institut für Physik, Universität Rostock, Albert-Einstein-Straße 23-24, 18059 Rostock, Germany.
authors.forename: S
authors.identifier: http://orcid.org/0000-0001-9729-8277
authors.initials: S
authors.lastname: Lochbrunner
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G.Bonchev str., bldg. 9, 1113 Sofia, Bulgaria. lantonov@orgchm.bas.bg.
authors.forename: L
authors.identifier: http://orcid.org/0000-0003-0520-1517
authors.initials: L
authors.lastname: Antonov