In Situ Discrimination between Axially Complexed and Ligand-Free Co Porphyrin on Au(111) with Tip-Enhanced Raman Spectroscopy

• Published in: Chemphyschem Vol. 10; no. 11; pp. 1794 - 1798
• Main Authors: Domke, Katrin F., Pettinger, Bruno
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 03.08.2009; WILEY‐VCH Verlag; Wiley
• Subjects: Adsorption; Chemistry; Cobalt - analysis; Cobalt - chemistry; Exact sciences and technology; General and physical chemistry; Gold - chemistry; Ligands; organometallic compounds; porphyrinoids; Porphyrins - analysis; Porphyrins - chemistry; scanning probe microscopy; Spectrum Analysis, Raman - methods; surface analysis; Surface physical chemistry; Surface Properties; tip-enhanced Raman spectroscopy (TERS); Complexation; Gold; Transition element complexes; Scanning probe microscopy; Nitrogen heterocycle; In situ; scanning probe microscopy ·surface analysis; Organometallic compound; Transition metal; Crystal face; Surface analysis; Cobalt complex; Cobalt; Complexes; Single crystal; Scanning tunneling microscopy; Scanning microscope; Metalloporphyrin; Raman spectrometry; tip-enhanced Raman spectroscopy (TERS); Structure; organometallic compound ·porphyrinoids
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200900182

Simultaneous chemical and topographic information about cobalt tetraphenyl‐porphyrin (CoTPP) adlayers formed on a Au(111) single crystal is obtained with tip‐enhanced Raman (TER) spectroscopy. We distinguish in situ between sample areas covered with an ordered adlayer of CoTPP and areas covered with a spontaneously formed disordered phase. The Raman vibrational fingerprints collected from the nanometer‐sized near‐field region just below a scanning tunnelling microscope (STM) tip are correlated with the adsorbate structures seen in the STM images. We assign the TER spectral features of the disordered phase to CoTPP complexes with CO and/or NO axial ligands, whereas the TER spectrum obtained from the ordered phase does not show any indication of additional axial complexation of CoTPP. Hot‐spotting CoTPP: Tip‐enhanced Raman spectra reveal binding events of CO and/or NO axial ligands to cobalt tetraphenyl porphyrin (CoTPP). Corresponding STM images show that while ligand‐free CoTPP forms well‐ordered adlayers on Au(111), the axially complexed molecules are adsorbed randomly at the surface (see figure).