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

Who: Dr. Daniel Wegner, Radbout Universiteit Nijmegen, Institute for Molecules and Materias, Nijmegen, The Netherlands

Place: Donostia International Physics Center. Pº Manuel Lardizabal 4, Donostia - San Sebastián

Date: Thursday, 19 May 2016, 12:00

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.

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