title: Q and Soret Band Photoexcitation of Isolated Palladium Porphyrin Tetraanions Leads to Delayed Emission of Nonthermal Electrons over Microsecond Time Scales.
abstract: We have used both action and photoelectron spectroscopy to study the response of isolated Pd(II) meso-tetra(4-sulfonatophenyl)porphyrin tetraanions ([PdTPPS](4-)) to electronic excitation over the 2.22-2.98 eV photon energy range. The action spectrum obtained by recording the wavelength-dependent intensity of charged decay products closely resembles the absorption spectrum of PdTPPS in aqueous solution (which shows pronounced Q and Soret absorption bands). The two main decay channels observed are sulfonate group loss and, predominantly, electron emission. To better understand the electron emission channel, we have also acquired photoelectron spectra at multiple detachment photon energies covering the range probed in action spectroscopy. Upon both Q and Soret band excitation, we find that electrons are emitted in three characteristic kinetic energy ranges. The corresponding detachment processes are identified as (delayed) tunneling emission from both excited singlet and triplet states (each of which is accessed by/after one-photon absorption) as well as resonant two-photon detachment. The first triplet state lifetime of isolated [PdTPPS](4-) is significantly longer than 10 μs, possibly on the 100 μs time scale. We estimate that more than 50% of the electron emission observed upon photoexcitation occurs by way of this triplet state.
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT) , Postfach 3630, 76021 Karlsruhe, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Jäger
authors.affiliation: Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT) , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
authors.forename: Katrina
authors.initials: K
authors.lastname: Brendle
authors.affiliation: Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT) , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Schwarz
authors.affiliation: Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT) , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Himmelsbach
authors.affiliation: Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT) , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
authors.forename: Markus K
authors.initials: MK
authors.lastname: Armbruster
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT) , Postfach 3630, 76021 Karlsruhe, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Fink
authors.affiliation: Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT) , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Weis
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT) , Postfach 3630, 76021 Karlsruhe, Germany.|Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT) , Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany.
authors.forename: Manfred M
authors.initials: MM
authors.lastname: Kappes