Taking a snapshot of the triplet excited state of an OLED organometallic luminophore using X-rays
Grigory Smolentsev, Christopher J. Milne, Alexander A. Guda, Kristoffer Haldrup, Jakub Szlachetko, Nicolò Azzaroli, Claudio Cirelli, Gregor Knopp, R. Bohinc, Samuel Menzi, Georgios Pamfilidis, Dardan Gashi, Martin Beck, A. Mozzanica, Daniel James, Camila Bacellar, Giulia F. Mancini, Andrei A. Tereshchenko, В. В. Шаповалов, Wojciech M. Kwiatek, Joanna Czapla–Masztafiak, Andrea Cannizzo, Michela Gazzetto, Mathias Sander, Matteo Levantino, Victoria Kabanova, Elena Rychagova, Sergey Yu. Ketkov, Marian Olaru, Jens Beckmann, Matthias Vogt
Abstract
OLED technology beyond small or expensive devices requires light-emitters, luminophores, based on earth-abundant elements. Understanding and experimental verification of charge transfer in luminophores are needed for this development. An organometallic multicore Cu complex comprising Cu-C and Cu-P bonds represents an underexplored type of luminophore. To investigate the charge transfer and structural rearrangements in this material, we apply complementary pump-probe X-ray techniques: absorption, emission, and scattering including pump-probe measurements at the X-ray free-electron laser SwissFEL. We find that the excitation leads to charge movement from C- and P- coordinated Cu sites and from the phosphorus atoms to phenyl rings; the Cu core slightly rearranges with 0.05 Å increase of the shortest Cu-Cu distance. The use of a Cu cluster bonded to the ligands through C and P atoms is an efficient way to keep structural rigidity of luminophores. Obtained data can be used to verify computational methods for the development of luminophores.