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An approach toward molecular information storage employs redox-active molecules attached to an electroactive surface. The chief advantages of such molecular capacitors include higher charge density and more versatile synthetic design than is afforded by typical semiconductor charge-storage materials. An architecture containing two triple-decker sandwich coordination complexes and an S-acetylthiomethyl-terminated tether has been designed for multibit storage. Each triple decker is composed of two phthalocyanines, one porphyrin, and two europium atoms. The oxidation potentials of each triple decker are tuned through the use of different substituents on the phthalocyanines (t-butyl, methyl, H) and porphyrins (pentyl, p-tolyl). Interleaving of the four cationic oxidation states of each triple decker potentially affords eight distinct oxidation states. Two dyads were examined in solution and in self-assembled monolayers (SAMs) on a Au surface. One dyad exhibited eight distinct states in solution and in the SAM, thus constituting a molecular octal counter. The potentials ranged from −0.1-+1.3 V in solution and +0.1-+1.6 V in the SAM. Taken together, this approach provides a viable means of achieving multibit information storage at relatively low potential.

In the present review, we show how the chemistry of lanthanide macrocyclic complexes, which began almost 50 years ago in Russia, is still very active. Additionally to bisphthalocyanines complexes, triple-decker, but also quadruple- and quintuple-decker complexes have been synthesized via new chemical routes. The driving force for the development of this chemistry arises from the wide range of possible applications. Owing to their very high conductivity, compared to that of monophthalocyanines, LnPc₂ and Ln₂Pc₃ complexes are used as molecular semiconductors in electronic devices. The radical nature of LnPc₂ complexes makes them easily oxidized and reduced. This is the reason why they are particularly promising materials for the development of new chemical sensors, associated with both conductimetric and optical transducers.