Self-Assembled Monolayers of Cobalt(II)− (4-tert-Butylphenyl)-Porphyrins:  The Influence of the Electronic Dipole on Scanning Tunneling Microscopy Images

Abstract

Self-assembled monolayers (SAMs) of cobalt(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrin, a promising material for optical, photoelectrochemical, and chemical sensor applications, were prepared on Au(111) via axial ligation to 4-aminothiophenol, and studied by several surface science techniques. Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements showed the apparent topology of the Au(111) herringbone structure reconstruction, but with bias-dependent contrast images and asymmetric I/V characteristics. Photoelectron spectroscopy confirmed the presence of metalloporphyrins on the surface, whereas near-edge X-ray absorption (NEXAFS) measurements revealed that the porphyrin ring was tilted by about 70 degrees with respect to the surface plane. The above effects are ascribed to the presence of oriented molecular dipole layers between the metal and the organic material as confirmed by a comparison with first-principles density-functional theory calculations. The measured bias-dependent STM profiles have been reproduced by a simple monodimensional tunneling model.

Rectification in Supramolecular Zinc Porphyrin/Fulleropyrrolidine Dyads Self‐Organized on Gold(111)

“…The 4-ATP/ZnTPP self-assembled monolayer (ZnTPP SAM) was produced by incubating bare AuA C H T U N G T R E N N U N G (111) in a solution of 4-ATP in ethanol followed by a solution of ZnTPP in chloroform. [52,62] Subsequently, the PyC 2 C 60 molecules were anchored to form dyads by dipping the ZnTPP SAM into a 10 À7 m solution of PyC 2 C 60 in toluene for approximately 20 s. Then, the sample was rinsed in warm toluene to remove excess PyC 2 C 60 . During this process, the MTPP ring is assumed to weaken the interaction with the 4-ATP amino group and create a stable axial link with the pyridyl moiety of PyC 2 C 60 .…”

Does the Surface Matter? Hydrogen‐Bonded Chain Formation of an Oxalic Amide Derivative in a Two‐ and Three‐Dimensional Environment

“…[3,8,10,[13][14][15] The restriction to a substrate not only modifies existing chiral properties, but novel and interesting chiral effects that are not possible for bulk materials also arise. [7,14,[16][17][18] Moreover, the interaction with the metal substrate can dictate a new conformation that differs remarkably from the geometry exhibited in the crystal phase and changes the functionality, as often experienced for porphyrins [19] and adaptive peptide or amino acid species. [7,20,21] Herein we report a multi-technique study of an oxalic amide derivative featuring the functional amide group that potentially forms hydrogen-bond motifs pivotal for the tertiary structures of a large number of biomolecules, in particular peptides.…”

Molecular Tips for Scanning Tunneling Microscopy: Intermolecular Electron Tunneling for Single-molecule Recognition and Electronics

“…The Au(111) substrate was initially modified with 4ATP via S-Au chemisorption; this 4ATP-modified substrate was then immersed in the CoTPP solution. These processes allow the immobilization of CoTPP on the Au surface through 4ATP by axial ligation, [58][59][60] with the consequent formation of the molecular assembly ( Fig. 10(a), right).…”