Synthesis and Surface Investigations of N-Substituted 2,5-Dithio-7- azabicyclo[2.2.1]heptanes on Gold Surfaces Sharwatie Ramsaywack, † Sanela Martic ́ , ‡ Scott Milton, † Lisa Gates, † Andrew S Grant,* ,† Mahmoud Labib, ‡ Andreas Decken, § and Heinz-Bernhard Kraatz* ,‡ † Department of Chemistry & Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1G8 ‡ Department of Physical and Environmental Sciences, University of Toronto at Scarborough, Toronto, ON, Canada, M1C 1A4 § Department of Chemistry, The University of New Brunswick, Fredericton, NB, Canada, E3B 6E2 * S Supporting Information ABSTRACT: The reaction of various primary amines and 2,5- dihydroxy-1,4-dithiane in the presence of a catalytic amount of Mg(II) in distilled water provided a series of N-substituted 2,5- dithia-7-azabicyclo[2.2.1]heptanes. The adsorption profiles of the sulfur-containing heterocycles on gold surfaces have been explored by time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), and electrochemistry. SIMS data indicated that these novel bicyclic sulfides interact with gold surfaces favorably, independent of the N-substitution, with minimal fragmentation. An XPS study revealed the three component core levels of S 2p with binding energies at 161, 162, and 163 eV, indicating a combination of the bound and unbound sulfur species. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we found the efficient adsorption of heterocycles onto gold and the formation of densely packed films for alkyl and phenyl analogues. However, the adsorption and film packing properties were greatly compromised by an N-pyridyl substitution. The findings indicate that the surface behavior of N-substituted 2,5-dithia-7- azabicyclo[2.2.1]heptanes varies with respect to the N-substitution and the nature of the substituent, suggesting that the adsorption profiles and the film packing of bicyclic sulfides on gold surfaces are highly dependent on the binding interface and the molecular orientation. ■ INTRODUCTION Self-assembling monolayers (SAMs) attract much attention due to their ability to control wetting adhesion, lubrication, and corrosion. 1-5 More recently, they have also been recognized as suitable candidates for use in chemical and biochemical sensors. 1,2 Probably, the most studied and well understood SAMs are those derived from alkanethiols (R-SH), dialkyl disulfides (R-S-S-R), and dialkyl sulfides (R-S-R) on gold surfaces. 3,4 However, the variation in the film formation and properties greatly varies between the ligands. SAMs prepared from thiols or disulfides have similar structures and were found to adsorb on gold surfaces via dissociative adsorption (cleavage of S-H and S-S bonds), which leads to the formation of well- packed and robust films. 4,6 By contrast, the adsorption profiles of dialkyl sulfides on gold surfaces have been previously described to proceed without the cleavage of the S-C bond by using a range of analytical techniques including X-ray photoelectron, infrared, scanning tunneling microscopy and high-resolution electron energy loss spectroscopies, and time- of-flight secondary ion mass spectrometry (TOF-SIMS). 7-12 The interactions of dialkyl sulfides with gold surfaces are based on the dative-type bonding through a lone pair of the sulfur atom in sulfides. While the sulfide films are characterized by a potentially compromised organization, robustness, and stability compared to the thiols or disulfides, the advantages associated with sulfides make this class of compounds of interest. 13-16 The sulfides exhibit greater stability and lower reactivity toward oxidation and nucleophilic attacks. The convenient synthesis and the inherent R-S-R structure of sulfides provide a convenient way toward developing new organosulfur targets through appropriate substitution (symmetrical or unsym- metrical) and for controlling the film composition on metal surfaces. In addition, the monolayers of some dialkyl sulfides have a very low defect density as compared to thiolates. 11 Recent discovery of the two surface-bound enantiomers on gold surfaces, formed by a butyl methyl sulfide, indicates that the gold-sulfur interactions in sulfides may induce a chiral surface environment. 17,18 Consequently, the potential use of dialkyl sulfides is in the area of surface functionalization and preparation of SAMs with interesting properties. Here, we explored a series of a new class of bicyclic sulfides to understand their interactions with gold surfaces and gauge their utility as precursors toward functional SAMs. In an effort to expand the repertoire of ligands available for the Received: January 26, 2012 Revised: March 15, 2012 Published: March 16, 2012 Article pubs.acs.org/JPCC © 2012 American Chemical Society 7886 dx.doi.org/10.1021/jp300866r | J. Phys. Chem. C 2012, 116, 7886-7896