Functional molecular machines

The development of supramolecular chemistry based on a particular cyclophane, namely, the cyclobis (paraquat-p-phenylene) (CBPQT 4+) is outlined in Chapter 1. From its emergence in 1988, the CBPQT4+ cyclophane and its variants have been widely incorporated in constructing mechanically interlocked molecules, such as catenanes and rotaxanes. In particular, the tetracationic cyclophane serves as the central movable part in numerous switchable molecular machines. It has also been harnessed in molecular memories. The future direction of these cyclophane-based molecular machines will involve real mechanical work.; Chapter 2 describes a range of covalently linked donor-acceptor compounds which contain (i) a hydroquinone (HQ) unit, (ii) a 1,5-dioxynaphthalene (DNP) ring system, and (iii) a tetrathiafulvalene (TTF) unit as the pi-donating arm component attached to (iv) cyclobis(paraquat- p-phenylene) (CBPQT4+) as the pi-accepting tetracationic cyclophane. These compounds were prepared and shown to operate as simple molecular machines. The pi-donating arm components can be included inside the cyclophane in an intramolecular fashion by virtue of stabilizing noncovalent bonding interactions. Such self-complexing equilibria were shown to be highly thermally or electrochemically controllable, observations which lead to applications of these self-complexing compounds as thermo- and electroswitches, as well as in sensing and imaging materials.; Chapter 3 describes the creation of a palindromic [3]rotaxane reminiscent of a molecular muscle. It was shown to generate internal contraction and extension movements under redox conditions. Disulfide tethers have been covalently attached to both of the ring components in the [3]rotaxane. An array of microcantilever beams, coated with a self-assembled monolayer of the [3]rotaxane molecules, undergoes controllable and reversible bending when it is exposed to chemical oxidants and reductants. This observation supports the hypothesis that the cumulative nanoscale movements within surface-bound "molecular muscles" can be harnessed to perform larger-scale mechanical work.; The design and synthesis of a family of conjugated polymers, which are essentially poly{lcub}(5-alkoxy-m-phenylenevinylene)- co-[(2,5-dioctyloxy-p-phenylene)vinylene]{rcub} (PAmPV) derivatives, is outlined in Chapter 4 . PAmPV Polymers solubilize SWNT bundles in organic solvents by wrapping themselves around the nanotube bundles. PA mPV Derivatives which bear tethers or rings form pseudorotaxanes with rings and threads, respectively. Wrapping of these functionalized PA mPV polymers around SWNTs results in the grafting of pseudorotaxanes along the walls of the nanotubes in a periodic fashion. The results hold out the prospect of being able to construct arrays of molecular switches and actuators.