title: Electronic Structure and Excited-State Dynamics of an Arduengo-Type Carbene and its Imidazolone Oxidation Product.
abstract: We describe an investigation of the excited-state dynamics of isolated 1,3-di-tert-butyl-imidazoline-2-ylidene (tBu2Im, C11H20N2, m/z=180), an Arduengo-type carbene, by time- and frequency-resolved photoionization using a picosecond laser system. The energies of several singlet and triplet excited states were calculated by time-dependent density functional theory (TD-DFT). The S1state of the carbene deactivates on a 100 ps time scale possibly by intersystem crossing. In the experiments we observed an additional signal at m/z=196, that was assigned to the oxidation product 1,3-di-tert-butyl-imidazolone, tBu2ImO. It shows a well-resolved resonance-enhanced multiphoton ionization (REMPI) spectrum with an origin located at 36951 cm-1. Several low-lying vibrational bands could be assigned, with a lifetime that depends strongly on the excitation energy. At the origin the lifetime is longer than 3 ns, but drops to 49 ps at higher excess energies. To confirm formation of the imidazolone we also performed experiments on benzimidazolone (BzImO) for comparison. Apart from a redshift for BzImO the spectra of the two compounds are very similar. The TD-DFT values display a very good agreement with the experimental data.
authors.affiliation: Institute of Physical und Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Schmitt
authors.affiliation: Institute of Physical und Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Flock
authors.affiliation: Institute of Physical und Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Eileen
authors.initials: E
authors.lastname: Welz
authors.affiliation: Institute of Physical und Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Bernd
authors.identifier: http://orcid.org/0000-0003-3057-389X
authors.initials: B
authors.lastname: Engels
authors.affiliation: Institute of Inorganic Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Heidi
authors.initials: H
authors.lastname: Schneider
authors.affiliation: Institute of Inorganic Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Udo
authors.initials: U
authors.lastname: Radius
authors.affiliation: Institute of Physical und Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Ingo
authors.identifier: http://orcid.org/0000-0001-8978-4013
authors.initials: I
authors.lastname: Fischer
keywords: DFT; carbenes; excited-state dynamics; photophysics; time-resolved spectroscopy