Oligomeric Metallocenes for Molecular Electronics
Final Report Abstract
This project investigated different metallocenes for their application in the formation of thin films on varying substrates. Finding reliable methods for depositing metallocenes and other organometalic substances on surfaces, that are compatible with their often limited stability, is an important step in making their application as building blocks in molecular electronics possible. Triferrocene and diiodotriferrocene were initially chosen for organic molecular beam deposition but it was found that their limited thermal stability prevents them from subliming and forming thin films with this technique. Spin coating and drop casting were next explored using triferrocene but due to the comparatively low solubility of this compound those experiments did not yield promising thin films either. As a consequence, the focus of the project shifted slightly to explore alternative methods for depositing organometalic compounds. Two related ferrocene species, 8 and 9, bearing cyclopentadiene substituents were identified as suitable candidates that can be deposited electrochemically onto glassy carbon and gold electrodes. Both can be used to achieve films on glassy carbon electrodes, gold electrodes and Si substrates with a convenient electrochemical set up within a short time frame. It was found that the optimal conditions include the application of 0.4 V vs. the sample’s E1/2 and that the maximum coverage was reached after about 1000 s for the monosubstituted species 8 and after 600 s for the disubstituted species 9. This deposition probably occurs via the cyclopentadiene-substituent and involves loss of the C- H-proton upon oxidation. This hypothesis is supported by experiments using related ferrocenes, in which that C-H position is blocked or entirely absent. None of these species could be deposited electrochemically. Deposition experiments in acidic solutions resulted in significantly lower coverage, providing further evidence that the electrochemical deposition is linked to proton loss. This electrochemical deposition is a fast and reliable method of immobilising metallocenes on various surfaces that is compatible with the thermal instability of metallocenes. Since this technique could also be used under inert conditions, it might enable the deposition of moisture- and air sensitive organometalic compounds and could contribute to the development of molecular electronic devices using a variety of metallocenes or related electrochemically active species. Finally, based on previous work of other members of the Long group, a ferrocyanine was successfully synthesized as proven by mass spectrometry and visible absorption spectroscopy.
