Molecular approach toward information storage based on the redox properties of porphyrins in self-assembled monolayers

A molecular approach to information storage is described that uses porphyrins attached to a Au microelectrode as the memory storage element. A set of four zinc porphyrins has been examined, with each porphyrin bearing three mesityl groups and one S-acetylthio-derivatized linker of structure 1-[AcS-(CH₂)_n]-4-phenylene (n=0, 1, 2, or 3). Each porphyrin forms a self-assembled monolayer (SAM) on the Au microelectrode. Information is stored in the multiple oxidation states (neutral, monocation, dication) of the porphyrin. The charge retention time for each of the porphyrin monocations is in the regime of hundreds of seconds and varies with molecular structure (t_1/2=116, 167, 656, and 885 s for n=0–3, respectively). The redox process in the SAM can be cycled thousands of times under ambient conditions without loss of signal, thus the loss in charge does not stem from decomposition. The fact that the system (1) is fabricated by self-assembly, (2) is addressed electrically, (3) operates under ambient conditions, (4) can be cycled multiple times, (5) requires no moving parts for reading and writing, and (6) is scalable to small dimensions make this approach attractive for molecular-based information storage. © 2000 American Vacuum Society.