Title

Synthesis and electrochemistry of films incorporating bipyridinium and tetrathiafulvalene building blocks

Date of Award

2004

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Francisco M. Raymo, Committee Chair

Abstract

This dissertation tackles the synthesis and electrochemistry of self-assembled films incorporating two building blocks, namely bipyridinium and tetrathiafulvalene. We have identified a simple experimental protocol to assemble electroactive films of these building blocks. The building block incorporating bipyridinium bisthiols adsorbs spontaneously on the electrode surface forming multiple electroactive layers. The resulting interfacial assemblies mediate the transfer of electrons from the electrode to the redox probes in the electrolytes solution, but prevent electron transfer in the opposite direction. The redox probe Ru(NH2)63+ showed a reversible reduction in the absence of a film of bipyridinium bisthiol on the electrode surface. However, when the electrode surface is coated with a film the bipyridinium bisthiol, the response of the redox probe Ru(NH2)6 3+ changes dramatically. Its reduction wave shifts in the negative direction overlapping with the bipyridinium reduction wave, and its oxidation is hindered. After the insertion of electroactive anionic dopant, Fe(CN) 64-, in the polycationic bipyridinium matrix, the transfer of electrons form the redox probes to the electrode becomes possible. Under these conditions, the probe reduction accompanies that of the surface-confined bipyridinium dications, while the probe re-oxidation follows the oxidation of the anionic dopants. This intriguing behavior imposes a large potential difference between the voltammetric reduction and oxidation peaks of the probe, which parallels the difference between the bipyridinium reduction and the dopant oxidation potentials. Thus, the careful selection of the electroactive dopant can be exploited to tune the electronic properties of the composite film. This chemical approach to interfacial assemblies with controlled dimensions and engineered properties can lead to electrode/organic film/electrode junctions with pre-defined current/voltage signatures.The building blocks incorporating tetrathiafulvalene (TTF) units self-assemble on gold to form electroactive monolayers that exhibit interesting blocking capabilities in the presence of electron acceptors acting as redox probes in the electrolyte solution, namely benzyl viologen (BV), tetracyanoquinodimethane (TCNQ), and teracyanoethylene (TCNE). Presumably, the TTF units in the monolayers form charge-transfer complexes with the electron acceptors present in solution. The presence of TTF SAMs on the electrode surface completely blocks the reduction of BV in solution, and causes the redox response of TCNQ and TCNE to be irreversible. (Abstract shortened by UMI.)

Keywords

Chemistry, Organic; Engineering, Materials Science

Link to Full Text

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