Molecular Switches Based on Donor-Acceptor, Radical and Coulombic Interactions - From Solution, to Solid-State to Application

This Thesis outlines in 10 Chapters my PhD research on molecular switches, which includes mechanistic investigations of host-gust complexes and mechanically interlocked molecules (MIMs). The first Chapter is an introduction to the syntheses, making use of Click Chemistry, and mechanisms of operation of some bistable MIMs and host-guest complexes reported in the literature. Chapters 2 and 3 describe an electrochemical methodology and quantitative evaluation for the ground-state distribution constants of a variety of bistable redox-active donor-acceptor MIMs, some of which have found applications in molecular memory devices. This electrochemical methodology is based on slow scan rate cyclic voltammetry and is widely applicable to a broad base of bistable donor-acceptor MIMs. In Chapter 4, I report on the use of electrostatic barriers as a means of slowing down the kinetics of shuttling in degenerate MIMs as well as host-guest complex formation. Electrostatic barriers can lower the rate constants associated with these processes by many orders of magnitude. Chapter 5 describes how these same electrostatic barriers can serve as thermodynamic recognition sites when in their radical cationic forms, while Chapter 6 expands in quantitative detail the mechanism of radical recognition in the context of host-guest chemistry, and Chapter 7, in the context of MIMs. Chapter 7 also elucidates how electrostatic barriers and radical recognition can work together to produce mechanostereoselective motion - a key component in the development of a Brownian ratchet mechanism. Chapter 8 describes how this radical recognition motif can be exploited in the realm of organic electronics, e.g., to make semiconducting materials from organic radical host-guest complexes for field-effect transistors. Chapter 9 presents a review of molecular switches on surfaces and devices reported in the literature. In Chapter 10, I discuss my perspectives on the future of molecular switches including a discussion of the Brownian ratchet mechanism, as well as my take on developing some new materials for the field of organic electronics based on radical host-guest chemistry.