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Development of New Electron-rich Organometallic Platforms Featuring Linear Azulenic and 6,6’-Biazulenic π-Linkers Equipped with Isocyanide and Thiolate Junctions
Applegate, Jason Chadwick
Applegate, Jason Chadwick
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Abstract
Azulene is a non-alternant, poly-aromatic hydrocarbon (PAH) that has garnered significant interest in the areas of molecular electronics, organometallics, and organic synthesis. Applications of azulene in these fields include the development of molecular wires, batteries, non- linear optics, dyes, solar cells, and liquid crystal displays. Our focus in the Barybin research lab has been on the design and implementation of organometallic azulenic scaffolds for probing the electron delocalization and charge storage capabilities of various azulenic frameworks. In this work, the synthesis and characterization of asymmetrically functionalized azulene derivatives will be described, and applications of these derivatives to the field of molecular electronics will be discussed.In chapter I, a comprehensive review of azulene in molecular electronic applications is presented. Emphasis is placed on assessing the structure-function relationship of molecular wires containing azulenic cores. Furthermore, literature related to azulene’s use as molecular wire or rectifier is surveyed. New design principles for azulene-based molecular wires or rectifiers are suggested based on the corresponding literature.In chapter II, the synthesis of the first molecule containing both isocyano and mercapto functionalities is presented. This isocyanothiol derivative, with applications in molecular rectification, is comprised of azulene substituted along its dipolar molecular axis at the 2- and 6- positions. Spectroscopic characterization, and hetero-bimetallic (Cr0/Au1+) complexation of the 2-isocyano-6- thiolazulene derivative is achieved. Additionally, a new, sensitive 13C NMR-based method for probing the donor - acceptor ratio of (OC)5Cr(2-isocyano-6-X-1,3-diethoxy-carbonylazulene)] (X = –N C, Br, H, SH, SCH2CH2CO2CH2CH3, SAuPPh3) is established, which highlights the tunability of the 2,6-azulenic framework. Furthermore, self-assembled monolayers (SAMs) on Au(111) of the azulenic isocyanothiol moiety surfaces were formed and characterized. The characterization methods provide support for an upright molecular orientation on the surface, consistent with a hollow-linear sulfur-gold binding mode.In chapter III, the synthesis, characterization, and hetero-bimetallic (Cr0/Au1+) complexation of the second molecule containing both isocyano and mercapto functionalities is presented. This system employs the symmetric 6,6’- biazulenic motif asymmetrically functionalized at the 2- and 2’- termini with isocyanide and thiol, respectively. The scaffold’s tunability is assessed utilizing the redox profiles of a series of biazulenic motifs. Electronic communication from one termini to the other mediated by the 6,6’- biazulenic core was monitored via the 13C NMR method presented in chapter II. SAMs consisting of the biazulenic isocyanothiol were formed on Au(111). Characterization of this monolayer provided a probe for the nature of the self-assembly in comparison to an analogous diisocyano 6,6’- biazulene.Chapter IV introduces the chemistry of a novel homoleptic electrochromic complex that has a ca. 6 nm diameter and features seven Cr(0) centers interlinked with six 2,2’-diisocyano-1,1’,3,3’-tetraethoxycarbonyl-6,6’-biazulene bridges. Electronic absorption and FTIR signatures of the “nanocomplex”, as well as its remarkable redox profile, are discussed in detail. By design, the nanocomplex was expected to show a reduction capacity of up to -12 units, as each biazulenic unit could, in principle, be reduced by 2e-‘s at mild potentials to form the closed-shell structure featuring a heptafulvalene unit fused in between two cyclopentadienide moieties. Additionally, the complex’s multi-electron oxidation capacity is governed by its seven chromium centers.
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2019-01-01
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University of Kansas
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Inorganic chemistry,