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43402-GB3
A Ligand-Based Approach to the Control of Supramolecular Topology and Preparation of Electrochromic Materials
We are using hybrid pyridine/thiophene compounds as ligands for Re(I) and Pt(II) to investigate, prepare and characterize a series of electrochromic (a substance whose color changes upon varying the applied voltage) materials. The systems we have looked at thus far hold potential for future use as sensors for small molecules whose output is either a change in color or conductivity. Concurrently, as we adjust the solubility and oxidation potential of our ligand systems, we are working on developing a new ligand-based synthetic methodology for the preparation of inorganic macrocycles, which we believe will allow us to prepare more topologically varied and complex macrocycles then current metal-based strategies allow.
Towards both of these goals we have prepared a series of pyridine/thiophene hybrid ligands where either thiophene, bithiophene, or ethylenedioxythiophene are bound to the 4-position of the pyridine. The pyridine portions of these ligands bind strongly to late transition metals such as Re(I) and Pt(II). The thiophene derivative portion of these molecules couple under oxidative conditions linking two ligands together through the formation of a new carbon-carbon bond. By preparing metal complexes that contain at least two equivalents of the hybrid ligands, one can prepare materials that are mixtures of macrocycles and oligomers of the starting monomers.
We have prepared films of the hybrid ligands, as well as Re(I) and Pt(II) metal complexes on a variety of surfaces such as Pt button electrodes, ITO covered glass plates, and stainless steel plates. We have compared these results to model systems, by either replacing pyridine on the hybrid ligands with a phenyl group, or by removing the thiophene portion of the ligand when it is attached to a metal center. This has given us the ability to isolate the electrochemistry of the metals, pyridines, and thiophene derivatives from each other. The materials are electrochromic as demonstrated by spectroelectrochemistry and vary in color from purple to orange to green depending on the ligand, metal, and oxidation state. The Pt(II) complexes we have characterized exhibit electrochemistry very similar to the ligands themselves, indicating that the Pt(II) molecular orbitals are not a very good energy match for allowing conductivity to occur across the systems. The Re(I) systems exhibit a richer variety of electrochemical responses where metal center and thiophene electrochemistry overlap resulting in polyelectrochromic systems. Our work has resulted in two publications, one in the Journal of Organometallic Chemistry and one in the journal Inoranic Chemistry. The results from these experiments have resulted in three poster presentations (two student, one PI) at national ACS meetings, one presentation at the Boston Regional Inorganic Conference (BRIC), one presentation at an Inorganic Gordon Conference, and several presentations at colleges in New England. We are now trying to expand these systems to examine their ability to act as sensors for small molecules, or for building more complex topological architectures.
