SIMPLE MECHANICAL MOLECULAR AND SUPRAMOLECULAR MACHINES - PHOTOCHEMICAL AND ELECTROCHEMICAL CONTROL OF SWITCHING PROCESSES

Photochemical control of a self-assembled supramolecular 1:1 pseudorot axane (formed between a tetracationic cyclophane, namely the tetrachlo ride salt of cyclobis(paraquat-p-phenylene), and 1,5-bis[2-(2-(2-hydro xy)ethoxy)ethoxy]naphthalene) has been achieved in aqueous solution, T he photochemical one-electron reduction of the cyclophane to the radic al trication weakens the noncovalent bonding interactions between the cyclophane and the naphthalene guest-pi-pi interactions between the pi -electron-rich and pi-electron-poor aromatic systems, and hydrogen-bon ding interactions between the acidic alpha-bipyridinium hydrogen atoms of the cyclophane and the polyether oxygen atoms of the naphthalene d erivative-sufficiently to allow the guest to dethread from the cavity; the process can be monitored by the appearance of naphthalene fluores cence. The radical tricationic cyclophane can be oxidized back to the tetracation in the dark by allowing oxygen gas into the system. This r eversible process is marked by the disappearance of naphthalene fluore scence as the molecule is recomplexed by the tetracationic cyclophane. This supramolecular system can be chemically modified such that the p i-electron-rich unit, either a naphthalene derivative or a hydroquinon e ring, and the tetracationic cyclophane are covalently linked, We hav e demonstrated that the pi-electron-rich residue in this system is tot ally ''self-complexed'' by the cyclophane to which it is covalently at tached. Additionally, the self-complexation can be switched ''off'' an d ''ion'' by electrochemical two-electron reductions and oxidations, r espectively, of the tetracationic cyclophane component, Thus, we have achieved the construction of two switches at the nanoscale level, one driven by photons and the other by electrons.