Self-Assembly of Azulenic Monolayer Films on Metallic Gold Surfaces

Abstract

Derivatives of azulene, an unusual nonbenzenoid aromatic hydrocarbon featuring fused five- and seven-membered sp2 carbon rings, are of substantial current interest in the design of advanced functional materials such as organic electronics. The overarching theme of this dissertation is the chemistry of new hybrid metal/azulene platforms featuring azulenic monolayer films anchored to the atomically flat metallic gold via isocyanide or thiolate junctions. One of the key aspects of this work addresses the influence of the junction group's nature on the formation, stability, reactivity, and physicochemical characteristics of azulenic self-assembled monolayer (SAM) films on the Au(111) surface. Both isocyanide and thiolate "alligator clips" in these SAMs were shown to induce approximately upright orientation of the azulenic framework with respect to the gold surface. The films' properties were evaluated by various means including surface-enhanced infrared spectroscopy and optical ellipsometry. Of particular significance are the initial examples of molecular films involving all three possible linear biazulenic scaffolds. These SAMs feature isocyanide junction groups and exhibit good stability toward ambient lighting and, in some cases, air atmosphere. Characterization of certain isocyano- and mercaptoazulenic molecular films reported herein was greatly facilitated by incorporation of ancillary nitrile infrared spectroscopic reporters into the azulenic scaffold. Such an approach constitutes a novel strategy in the surface chemistry of organic thiols, to the best of the author's knowledge. In addition, the thesis describes, among other isocyanide/thiol competitive binding investigations, the first monolayer film displacement studies involving the RSH and RNC species with identical substituents R that underscore the higher affinity of the thiolate versus isocyanide junctions for metallic gold. Accessibility of the new monolayer films reported in this dissertation paves the way for future experimental validation of the theoretically predicted low resistivity of the linear 2,6-azulenic framework.