Electrically driven fluorescence of single-molecule junctions

CIC nanoGUNE Seminars

Michael Chong (Univ. Strasbourg)
Donostia International Physics Center
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Electrically driven fluorescence of single-molecule junctions A study of the optoelectronic properties of molecular junctions performed by scanning tunneling microscopy (STM) is presented. First, the molecular structures are synthesized on a Au(111) surface : an emitting unit (fused-porphyrin) is embedded in a molecular wire (oligothiophene) by means of on-surface polymerization. Then, by manipulation we lift and suspend the emitter between the tip of the STM and the gold surface, creating a single molecule junction. The molecular wire acts as an organic linker that allows the flow of electrons and decouples the fused-porphyrin from the metallic leads. By applying a voltage bias between the tip and the sample, a current is generated, which leads to the excitation of the molecule. This process is mediated by the localized surface plasmon modes of the tip. Eventually, the molecule de-excites in a radiative way, generating a fluorescence signal. This type of junction generates a narrow-line emission of light whose color is controlled by selecting the chemical structure of the emitting unit. Moreover, control over the linewidth is obtained by progressively detaching the emitting unit from the surface. Also, we observe red-shifted vibronic features that provide a chemical fingerprint of the emitter, and blue-shifted vibronic features that are a sign of hot-luminescence. (host: Nacho Pascual at nanoGUNE)