Imaging Porphyrin-Based Molecules on a Gold Substrate in Ambient Conditions

Covalently tethering porphyrin-based molecules to an otherwise inert gold substrate allows them to be imaged in an ambient environment using scanning tunneling microscopy. Interpretation of the data is aided by comparing images of mono- and diporphyrin molecules taken with the same tip. At low coverage we obtain a markedly larger average particle size (396 Ų) for diporphyrins than for monoporphyrins (121 Ų). The particle size distributions are very broad, but the images show a characteristic variation of contrast with tip bias, suggesting that the heterogeneity is due to different molecular conformations rather than contamination. We find evidence of ordered structures at high coverage.