Synthesis of Molecular Electronic Components for Self-Assembly Onto Metal Electrodes

Molecular electronics encompasses the synthesis and study of single-molecule electronic devices. Such devices have the potential to be smaller and more efficient than their silicon-based analogs. Our present goal is to design and synthesize a carbon-based molecular diode. Current work is centered on molecules bearing an electron-rich dimethoxybenzene donor ring and an electron-poor quinone acceptor ring separated by a single bond. We have successfully synthesized a template molecule, dibromohemibiquinone – which can then be converted to aminohemibiquinone – that will allow for the substitution of functional groups at its attachment sites. The purpose of such groups is bonding to metal electrode surfaces. Through deprotonation and acylation at the amino site of aminohemibiquinone, it is possible for attachment groups to be added to the hemibiquinone framework. Some particularly useful groups for bonding to metal surfaces are nitriles and thiols. A benzoyl nitrile moiety has been incorporated via cyanobenzoyl chloride. In order to append a thiol group, we have prepared 4,4’-dithiodibenzoic acid. Transformation of the acid into the acid chloride then allows for acylation of the aminohemibiquinone molecule. Once this substitution is completed, surface studies will be conducted on both the nitrile- and thiol-containing compounds in order to determine the geometry of a monolayer of self-assembled molecules on a gold surface. Monolayer geometry is essential, since the purpose of the diode is to allow unidirectional electron flow between two surfaces via attachment to each. Ideal surface geometry would be near perpendicular. In addition, derivatives of the hemibiquinone backbone have been synthesized for electrochemical and spectral comparison with the hemibiquinones.