title: Self-assembly of insoluble porphyrins on Au(111) under aqueous electrochemical control.
abstract: Self-assembled monolayers of a water-insoluble porphyrin, tetraphenyl porphyrin (TPP), in the presence of an aqueous electrolyte were characterized in situ with electrochemical scanning tunneling microscopy (EC-STM) at working electrode potentials of between 0.5 and -0.2 V. Isolated domains of TPP monolayers with differing orientation were observed on Au(111) in 0.1 M HClO(4) over this entire potential window. Individual TPP molecules could be resolved over a range of 700 mV, from open circuit potential (OCP) to near the hydrogen evolution potential. The unit cell is square, and the distance between neighboring molecules is about 1.4 ± 0.1 nm. High-resolution images allow the internal molecular structure to be discerned. No changes in the STM contrast of individual molecules were observed as the potential was changed. In a neutral electrolyte (0.1 M KClO(4), pH ~6), the potential range of stability of ordered structures is reduced. On HOPG, TPP forms ordered hexagonal structures with a lattice constant of about 2.6 nm in the double-layer potential region in 0.1 M HClO(4).
authors: Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
authors: Sedigheh
authors: S
authors: Sadegh Hassani
authors: Youn-Geun
authors: YG
authors: Kim
authors: Eric
authors: E
authors: Borguet
mesh_terms: D000327:Adsorption; D004563:Electrochemistry; D004566:Electrodes; D004573:Electrolytes / Q000737:chemistry; D004581:Electronics / Q000379:methods*; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D016252:Microscopy, Scanning Tunneling; D015394:Molecular Structure; D010472:Perchlorates / Q000737:chemistry; D011166:Porphyrins / Q000032:analysis* / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D010472:Perchlorates; D011166:Porphyrins; C409084:tetraphenylporphyrin; D014867:Water; D006046:Gold