sp-Hybridized carbon as a building block in the synthesis of molecules and materials

点击翻译按钮获取中文摘要

Introduction. This proposal outlines synthetic routes to carbon-rich molecules with defined structure using sp-hybridized carbon as a key building block. These molecules are designed to give answers to both fundamental and applied questions in chemistry, as well as physics and materials science. This program follows a “physical organic chemistry” approach: We examine detailed relationships between chemical structure and molecular reactivity/properties, commonly via thermal analyses, electrochemical methods, X-ray crystallography, as well as NMR, emission, and absorption spectroscopies (EPR, vibrational, and transient absorption spectroscopies are used via collaboration). Often, our molecules are designed to answer specific questions posed by collaborators in, for example, molecular electronics and solar energy capture. The proposed research program relies on four interrelated themes. ***1. Acetylene based structures. We will develop new strategies for the synthesis of conjugated polyynes to serve as functional materials and to model the properties of carbyne (the carbon allotrope constructed of sp-hybridized carbon). As high-energy molecules, polyynes are particularly challenging targets, and we will explore new stabilization schemes to meet these challenges. Supramolecular strategies are a specific focus, through synthesis of rotaxanes. Rotaxination is a key design motif, since it allows functionalization at the ends of a polyyne, e.g., for attaching molecular wires to electrodes or forming donor-acceptor polyynes. ***2. Cumulene based structures. [n]Cumulenes (n is the number of cumulated double bonds) provide an alternative structure toward understanding the properties of carbyne. Many chemical, electronic, and optical properties for [n]cumulenes are currently unknown, and we intend to answer seminal questions concerning bonding in cumulenes, such as rotational barriers and bond length alternation. Cumulenes will also be used as reactive precursors to form carbon-rich architectures and polymers via a new topochemical polymerization reaction. ***3. Molecular wires. We will explore and optimize cumulenes and polyynes to function as molecular wires. Endgroups are chosen to facilitate binding to electrodes such as gold and graphene. This project benefits distinctly from stabilization of polyynes and cumulenes as rotaxanes (Parts 1 and 2), which mimic insulated molecular wires. ***4. Synthetic carbon allotropes: Graph(di)yne structures. The solution-state synthesis carbon allotropes composed of sp- and sp2-hybridized carbon (graphyne and graphdiyne), is difficult due to a lack of selectivity during polymerization. We will use a templated approach based on new building blocks derived from triethynylmethanol (TEtM). TEtMs can be easily varied at the termini of the alkynes and the alcohol “leaving group” toward optimizing binding and reactivity on metals.