title: A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence.
abstract: Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)3]3+(where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d5complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Pavel
authors.initials: P
authors.lastname: Chábera
authors.affiliation: Center for Analysis and Synthesis (CAS), Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Yizhu
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Center for Analysis and Synthesis (CAS), Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Om
authors.initials: O
authors.lastname: Prakash
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Erling
authors.initials: E
authors.lastname: Thyrhaug
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Amal El
authors.initials: AE
authors.lastname: Nahhas
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Alireza
authors.initials: A
authors.lastname: Honarfar
authors.affiliation: Center for Analysis and Synthesis (CAS), Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Sofia
authors.initials: S
authors.lastname: Essén
authors.affiliation: Division of Theoretical Chemistry, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Fredin
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.|Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Tobias C B
authors.initials: TC
authors.lastname: Harlang
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.|Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Kasper S
authors.initials: KS
authors.lastname: Kjær
authors.affiliation: Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
authors.forename: Karsten
authors.initials: K
authors.lastname: Handrup
authors.affiliation: Division of Theoretical Chemistry, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Fredric
authors.initials: F
authors.lastname: Ericson
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Tatsuno
authors.affiliation: National Institute of Standards and Technology, Boulder, Colorado 80305, USA.
authors.forename: Kelsey
authors.initials: K
authors.lastname: Morgan
authors.affiliation: Division of Synchrotron Radiation Research, Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
authors.forename: Joachim
authors.initials: J
authors.lastname: Schnadt
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Lennart
authors.initials: L
authors.lastname: Häggström
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Tore
authors.initials: T
authors.lastname: Ericsson
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala, Sweden.
authors.forename: Adam
authors.initials: A
authors.lastname: Sobkowiak
authors.affiliation: Center for Analysis and Synthesis (CAS), Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Sven
authors.initials: S
authors.lastname: Lidin
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden.
authors.forename: Ping
authors.initials: P
authors.lastname: Huang
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden.
authors.forename: Stenbjörn
authors.initials: S
authors.lastname: Styring
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Jens
authors.initials: J
authors.lastname: Uhlig
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark.
authors.forename: Jesper
authors.initials: J
authors.lastname: Bendix
authors.affiliation: Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden.
authors.forename: Reiner
authors.initials: R
authors.lastname: Lomoth
authors.affiliation: Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Villy
authors.initials: V
authors.lastname: Sundström
authors.affiliation: Division of Theoretical Chemistry, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Petter
authors.initials: P
authors.lastname: Persson
authors.affiliation: Center for Analysis and Synthesis (CAS), Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Wärnmark