Grant: Discovery Grants Program - Individual

Introduction. This proposal outlines synthetic routes to carbon-rich molecules with defined structures using alkynes as the key building block. These molecules are designed to answer to both fundamental and applied questions in chemistry, as well as physics and materials science. My program follows a physical organic chemistry approach: We examine detailed relationships between chemical structure and molecular properties, commonly via thermal analyses, electrochemical methods, X-ray crystallography, as well as NMR, vibrational, emission, and absorption spectroscopies. Often, our molecules are designed to answer specific questions posed by collaborators in, for example, molecular electronics and solar energy capture. This program relies on four interrelated research goals. 1. Polyyne structures. Our goal is to develop new synthesis of conjugated polyynes, which serve as functional materials and models of carbyne (the allotrope constructed of sp-hybridized carbon). As high-energy molecules, polyynes are particularly challenging, and we will exploit new stabilization schemes to meet these challenges. Supramolecular strategies are specifically useful (e.g., rotaxanes) and also allow functionalization at the ends of a polyyne for attaching insulated molecular wires to electrodes. The mechanism of a new reaction we have discovered featuring Cu-catalyzed C-C bond activation in polyyne will also be explored. 2. Cumulene structures. [n]Cumulenes (n is the number of cumulated double bonds) provide an alternative structure toward understanding the properties of carbyne. We propose designs for stabilization and synthesis of unprecedented structures to shed light on the chemical, electronic, and optical properties of [n]cumulenes, many of which are currently unknown. Cumulenes will also be used as reactive precursors to form carbon-rich architectures and molecular wires through appropriate functionalization. The concept of electrohelicity will be explored as a fundamentally new way to describe orbitals in conjugated molecules and a potentially new means form to chiral molecules. 3. Acene-based structures. We hypothesize that the stepwise substitution of acenes will allow incorporation of groups to provide stability, solubility, and function. We target molecules that will facilitate solar energy conversion through the processes of singlet fission and triple-triplet annihilation upconversion. Careful molecular design is combined with world-leading theoretical and photophysical characterization to enhance the efficiency of organic molecules for next generation solar cells. 4. Graphyne structures. We predict that large molecular segments of new carbon allotropes composed of sp- and sp2-hybridized carbon (graphynes) can be formed by solution-state synthesis. With the appropriate design, we will use these molecules to approximate the properties of the unknown materials 6,6,12- and 30,30,30-graphyne, especially in comparison to the 'wonder material' graphene.