Calixpyrrole-based molecular self-assembly
Over the last two decades, calixpyrroles – teterapyrrolic macrocycle linked through α or meso-like positions by sp³-hybridized carbon atoms – have been exploited as strong and selective receptors and as extractants for both anions and ion pairs. In particular, complexation of an anion to calixpyrrole via four hydrogen bonds drives conformational changes from the 1,3- alternate to the cone conformation. This conversion provides a concave, bowl-like cavity that permits recognition of charge diffuse cations, such as cesium and imidazolium, through cation–𝜋 interactions. This structural flexibility is a characteristic of calixpyrrole chemistry. The work described in this dissertation takes advantage of molecular switching phenomena. In particular, it details efforts to realize self-assembly using functionalized calixpyrroles. In the context of theses efforts, a variety of secondary forces, such as hydrogen bonding interaction, 𝜋 - 𝜋 (CH-𝜋) interactions, and charge transfer (CT) interactions are exploited and studied in detail. Also included in this dissertation is a summary of studies of stimulus-responsive behavior, wherein systems constructed from calixpyrroles are exposed to external stimuli that includes anions, acid/base, and electrochemical triggers. Chapter 1 gives a brief overview of the use of calixpyrroles as molecular carriers stressing the transport of ion pairs. Chapter 2 details a multi-stage molecular equilibrium system that exploits two kinds of calipyrroles as well as appropriately chosen chemical inputs, and the conseqyent construction of a NAND logic gate. Chapter 3 describes factors that affect the self-assembly process under condition where the interactions are relatively weak. Chapter 4 focuses on orthogonal self-assembly from calixpyrrole and a functionalized fullerene. Chapter 5 details formation of metal-containing 1D arrays and molecular capsules. Lastly, chapter 6 demonstrates the syntheses and the characterization data of all compounds used in these studies.