Redox-active inorganic cages and pi-conjugation: covalent and non-covalent control of electronic coupling for chemical sensing, molecular switching, charge transport, and electrocatalysis

This thesis describes new design principles, synthetic strategies, and practical applications of redox-active small molecules and conducting polymers (CPs). We have prepared a series of CPs to exploit a tight electronic coupling between an electron-deficient main-group element and carbon-rich pi-conjugation. Cage-type borasiloxane repeating units that constitute such pi-extended structural platform support trivalent boron centers that engage in reversible bond-forming reactions with Lewis basic small molecules and ions. A colorimetric detection of volatile amine vapors by these inorganic-organic hybrid materials is described in Chapter I.;The general applicability of our structure assembly strategy is demonstrated further by the metal-containing CPs described in Chapter II. A metal-templated condensation reaction between dioximes and bithienylboronic acids facilitated access to transition metal clathrochelate complexes. Sequential electropolymerization of isostructural monomers that differ only in the encapsulated metal centers furnished conductive bilayer structures. A detailed investigation of the structural organization and interlayer charge transport properties of these hybrid materials constitutes the main topic of Chapter II.;In metal-containing CPs, both electrons and holes can be delivered to the redox-active metal centers via different pathways and with different rates. Chapter III describes detailed electrochemical, spectroelectrochemical, and cross-section imaging studies of p- and n-doped metal-containing CPs to describe this finding and its implications.;Reducing equivalents injected to such metal-containing CPs can also be utilized further for coupling of protons to produce hydrogen under electrocatalytic conditions, the underlying molecular mechanism of which is discussed in Chapter IV.;In response to injection or removal of electrons, metal-ligand assemblies undergo structural changes. A conceptually similar geometric relaxation was designed into a conformationally semi-rigid pi-conjugation having two tetrathiafulvalene (TTF) groups as "redoxphores". Redox-dependent structural folding and unfolding of this C2-symmetric molecule are influenced strongly by molecule--solvent and molecule--ion interactions, which also regulate charge delocalization through pi--pi contacts. This intriguing concept of conformational control by well-defined redox chemistry is described in Chapter V.