Cycloparaphenylenes as Building Blocks for Self-Assembled Nanotube-like Structures

Abstract

Since its first synthesis in 2008, the cycloparaphenylene (CPP), or “carbon nanohoop”, has quickly evolved from a synthetic novelty to a readily accessible and highly tunable molecular scaffold. With accessibility no longer an issue, many researchers have begun exploring how the unique properties of CPPs can be practically utilized. Chapter I provides an overview of the emerging applications of CPPs in a variety of fields, ranging from chemical biology to organic electronics.

Inspired by the long-standing challenge of synthesizing carbon nanotubes (CNTs) in a precise, size-selective fashion, we aimed to develop methods to use CPPs (which themselves represent fragments of CNTs) as supramolecular synthons to produce highly tunable CNT mimics. Chapter II discloses our initial effort toward this, showing how fluorination of the [12]CPP backbone results in CNT-like nanohoop self-assembly via organofluorine interactions. In Chapter III, we present the synthesis of two additional fluorinated nanohoops, one of lesser diameter and one bearing a lower degree of fluorination, and show that both molecules exhibit tubular self-assembly in the solid-state. These materials were found capable of a variety of functions, such as linear solid-state guest alignment and appreciable N2 uptake. Additionally, in Chapter IV, we show that fluorination of the nanohoop backbone may provide a means of improving π-π interactions between nanohoops in order to improve solid-state charge transfer. Preliminary data is provided showing that thin-films of a fluorinated [10]CPP analog exhibit an average conductivity ten-times higher than those of the non-fluorinated analog.

Having established a reliable strategy for constructing CPP-based non-covalent CNT mimics, we began pursuing a perhaps loftier goal of producing fully covalent CNT-like systems using nanohoops. In Chapter V, we present our initial foray towards this goal via the synthesis of a catechol containing nanohoop that, via proton NMR experiments, is shown to be readily capable of undergoing condensation reactions with boronic acids to form structures with boronic ester linkages. These results suggest that more complex boronic ester-linked nanohoop systems such as nanotubes and cages are indeed accessible.

This dissertation includes previously published and unpublished co-authored material.