Regensburg 2022 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 74: Organic Molecules at Surfaces 5: Molecular Switches
O 74.5: Vortrag
Donnerstag, 8. September 2022, 16:00–16:15, S054
Bipolar single-molecule electrofluorochromism — •Tzu-Chao Hung1, Roberto Robles2, Brian Kiraly1, Julian H. Strik1, Bram A. Rutten1, Alexander A. Khajetoorians1, Nicolas Lorente2, and Daniel Wegner1 — 1Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands — 2Centro de Fisica de Materiales, CFM/MPC (CSIC-UPV/EHU), Paseo de Manuel de Lardizabal 5, 20018 Donostia-San Sebastián, Spain
The interplay between the charge state and the fluorescence of a molecule is not only important for the spectroscopic analysis of chemical reactions, but electrofluorochromic molecules can also be utilized in displays, sensors, and switches. To understand the fundamental mechanisms on the single-molecule level, we studied the transient charged state of zinc phthalocyanine (ZnPc) adsorbed on ultrathin NaCl films on Ag(111) by combining scanning tunneling microscopy (STM) and spectroscopy (STS) with STM-induced luminescence (STML). We found evidence for both cationic ([ZnPc]+) and anionic ([ZnPc]−) fluorescence, depending on the polarity of the tip-sample bias. By carefully mapping the molecular frontier orbitals over a wide energy range, correlating them with onset energies for light emission and comparing with results from DFT calculations, we propose an alternative charging and electroluminescence mechanism. Our study provides new insights into the tunability of molecular optical response, as well as novel aspects toward utilization of bipolar electrofluorochromism in devices.