Finding and tuning electronic "set screws" in molecular magnets and phosphorescent complexes

DIPC Seminars

Dr. Daniel Wegner, Radbout Universiteit Nijmegen, Institute for Molecules and Materias, Nijmegen, The Netherlands
Donostia International Physics Center. Pº Manuel Lardizabal 4, Donostia - San Sebastián
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Finding and tuning electronic "set screws" in molecular magnets and phosphorescent complexes The spatial and electronic distribution of molecular frontier orbitals in functional molecules determine their electronic, optical and magnetic properties as well as their coupling to the local environment. The simultaneous high spatial and energy resolution of combined cryogenic scanning tunneling microscopy and spectroscopy enable the identification and visualization of molecular frontier orbitals in great detail. Embedding this method in a synergetic interplay with chemical synthesis and DFT calculations allows to thoroughly understand intra- and intermolecular coupling as well as molecule-substrate interactions. More specifically, we can identify molecular "set crews" that permit to tune the electronic properties appropriately with a specific applicability in mind. We have employed this strategy in two different cases. In the first example, we have investigated Pt-based phosphorescent molecules ("triplet emitters", used in OLED devices) on metallic and insulating substrates. We identified a peculiar hybridization that may be utilized to tune charge- injection barriers, and we found ways to independently tune the HOMO and LUMO levels that determine the emission color. Through these findings we were able to design and realize a deep-blue emitter. In the second example, we have investigated single-molecule magnets on various surfaces. We have identified electronic "weak links" in the organic ligand, which significantly reduces the spin coupling between transition-metal atoms. Subtle changes of the chemical structure and the active use of molecule-substrate coupling can improve the coupling strength significantly.