title: Direct observation of intersystem crossing in a thermally activated delayed fluorescence copper complex in the solid state.
abstract: Intersystem crossing in thermally activated delayed fluorescence (TADF) materials is an important process that controls the rate at which singlet states convert to triplets; however, measuring this directly in TADF materials is difficult. TADF is a significant emerging technology that enables the harvesting of triplets as well as singlet excited states for emission in organic light emitting diodes. We have observed the picosecond time-resolved photoluminescence of a highly luminescent, neutral copper(I) complex in the solid state that shows TADF. The time constant of intersystem crossing is measured to be 27 picoseconds. Subsequent overall reverse intersystem crossing is slow, leading to population equilibration and TADF with an average lifetime of 11.5 microseconds. These first measurements of intersystem crossing in the solid state in this class of mononuclear copper(I) complexes give a better understanding of the excited-state processes and mechanisms that ensure efficient TADF.
authors.affiliation: Institute of Organic Chemistry, Karlsruhe Institute of Technology, Kaiserstraße 12, 76131 Karlsruhe, Germany.; CYNORA GmbH, Werner-von-Siemensstraße 2-6, Building 5110, 76646 Bruchsal, Germany.
authors.forename: Larissa
authors.initials: L
authors.lastname: Bergmann
authors.affiliation: Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK.
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Hedley
authors.affiliation: CYNORA GmbH, Werner-von-Siemensstraße 2-6, Building 5110, 76646 Bruchsal, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Baumann
authors.affiliation: Institute of Organic Chemistry, Karlsruhe Institute of Technology, Kaiserstraße 12, 76131 Karlsruhe, Germany.; Karlsruhe Institute of Technology (KIT), Institute of Toxicology and Genetics, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bräse
authors.affiliation: Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK.
authors.forename: Ifor D W
authors.initials: ID
authors.lastname: Samuel
mesh_terms: D003300:Copper / Q000737:chemistry*; D005453:Fluorescence; D006358:Hot Temperature; D049449:Luminescence; D013050:Spectrometry, Fluorescence / Q000379:methods; D013696:Temperature
chemical_list: D003300:Copper
keywords: Thermally activated delayed fluorescence; copper complex; intersystem crossing; organic light-emitting diode; time-resolved photoluminescence