Reports: GB3
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.
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 close 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 Inorganic
Chemistry. The results from these
experiments have resulted in four poster presentations (two student, one PI) at
national
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. We are also looking to expand into new ligand systems using our expertise with Mannich Condensations to build a series of four six-coordinate (as opposed to the mono- coordinating pyridine ligands) thiophene/aminophenol complexes.