Synthesis of thiol-derivatized ferrocene-porphyrins for studies of multibit information storage

One approach toward storage Df multiple bits of information at the molecula r level requires the construction of molecular architectures comprised of m ultiple redox-active units. Four new ferrocene-porphyrins have been synthes ized to investigate questions concerning (i) the scope of redox-active mole cules that can be employed in molecular information-storage schemes and (2) writing/reading rates as well as retention of charge in redox-active units located at different sites in a molecular architecture. Three of the ferro cene-porphyrins have linkers of different lengths between the ferrocene and porphyrin. The fourth ferrocene- porphyrin has two ferrocenes positioned a t the lateral sites on the porphyrin. The latter architecture is designed t o provide a shorter distance between the electroactive surface and the ferr ocene while maintaining an upright; orientation of the porphyrin. Each ferr ocene-porphyrin affords three cationic oxidation states (ferrocene monocati on, porphyrin monocation, porphyrin dication) in addition to the neutral st ate, thereby affording the capability of storing two bits of information. E ach ferrocene-porphyrin bears an S-acetyl or S-(N-ethyl)carbamoyl-protected thiol moiety, thereby avoiding handling of free thiols. Each ferrocene-por phyrin forms a self-assembled monolayer (SAM) on gold via in situ cleavage of the thiol protecting group. The SAM of each array is electrochemically r obust and exhibits three well-resolved, reversible oxidation waves.