title: Excited State Potential Energy Surfaces of Polyenes and Protonated Schiff Bases.
abstract: The potential energy surface of the (1)Bu and (1)A' states of all-trans-polyenes and the corresponding protonated Schiff bases have been studied at density functional theory and coupled cluster levels. Linear polyenes and protonated Schiff bases with 4 to 12 heavy atoms have been investigated. The calculations show remarkable differences in the excited state potential energy surfaces of the polyenes and the protonated Schiff bases. The excited states of the polyenes exhibit high torsion barriers for single-bond twists and low torsion barriers for double-bond twists. The protonated Schiff bases, on the other hand, are very flexible molecules in the first excited state with low or vanishing torsion barriers for both single and double bonds. Calculations at density functional theory and coupled cluster levels yield qualitatively similar potential energy surfaces. However, significant differences are found for some single-bond torsions in longer protonated Schiff bases, which indicate a flaw of the employed time-dependent density functional theory methods. The close agreement between the approximate second and third order coupled cluster levels indicates that for these systems calculations at second order coupled cluster level are useful in the validation of results based on time-dependent density functional theory.
authors.affiliation: Institut für Physikalische Chemie, Universität Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany.|Department of Chemistry, P.O. Box 55 (A.I. Virtanens plats 1), University of Helsinki, FI-00014 Helsinki, Finland.|Lundbeck Foundation Centre for Theoretical Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Århus C, Denmark.|Physics Institute, Kazimierz Wielki University, Plac Weyssenhoffa 11, PL-85-072 Bydgoszcz, Poland.
authors.forename: Robert
authors.initials: R
authors.lastname: Send
authors.affiliation: Institut für Physikalische Chemie, Universität Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany.|Department of Chemistry, P.O. Box 55 (A.I. Virtanens plats 1), University of Helsinki, FI-00014 Helsinki, Finland.|Lundbeck Foundation Centre for Theoretical Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Århus C, Denmark.|Physics Institute, Kazimierz Wielki University, Plac Weyssenhoffa 11, PL-85-072 Bydgoszcz, Poland.
authors.forename: Dage
authors.initials: D
authors.lastname: Sundholm
authors.affiliation: Institut für Physikalische Chemie, Universität Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany.|Department of Chemistry, P.O. Box 55 (A.I. Virtanens plats 1), University of Helsinki, FI-00014 Helsinki, Finland.|Lundbeck Foundation Centre for Theoretical Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Århus C, Denmark.|Physics Institute, Kazimierz Wielki University, Plac Weyssenhoffa 11, PL-85-072 Bydgoszcz, Poland.
authors.forename: Mikael P
authors.initials: MP
authors.lastname: Johansson
authors.affiliation: Institut für Physikalische Chemie, Universität Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany.|Department of Chemistry, P.O. Box 55 (A.I. Virtanens plats 1), University of Helsinki, FI-00014 Helsinki, Finland.|Lundbeck Foundation Centre for Theoretical Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Århus C, Denmark.|Physics Institute, Kazimierz Wielki University, Plac Weyssenhoffa 11, PL-85-072 Bydgoszcz, Poland.
authors.forename: Filip
authors.initials: F
authors.lastname: Pawłowski