Studies related to the design and synthesis of a molecular octal counter

An approach to the storage of multiple bits of information at the molecular level employs molecules with a large number of distinct oxidation states. Europium triple-decker sandwich molecules composed of porphyrins and phthal ocyanines afford four cationic states and are very attractive for molecular information-storage applications. A larger number of states can be achieve d by combinations of triple deckers that afford interleaved oxidation poten tials. In order to identify suitable candidates for effective interleaving of oxidation potentials, a library of 19 new triple-decker complexes was pr epared. Electron-donating groups have been attached to the porphyrin and/or phthalocyanine moieties in order to achieve oxidation states in the low po tential regime. The triple deckers are of three different types: (Pc)Eu(Pc) Eu(Por), (Pc)Eu(Por)Eu(Pc), and (Por)Eu(Pc)Eu(Por). The solution electroche mistry of each member of the library was examined. These studies revealed s uitable pairs of triple deckers that provide effective interleaving of oxid ation potentials. Six triple deckers of type (Pc)Eu(Pc)Eu(Por) were derivat ized with a thioacetyl or thiocyanate group on the porphyrin unit for attac hment to an electroactive surface. Each of the S-(acetylthio)-derivatized t riple deckers forms a self-assembled monolayer (SAM) on Au via in situ clea vage of the thiol protecting group. The SAM of each triple decker is electr ochemically robust and exhibits four, well-resolved reversible oxidation wa ves. Upon disconnection from the source of applied potential, the triple-de cker SAMs retain charge for tens to hundreds of seconds. The exact value of the charge-retention time depends on the specific porphyrin/phthalocyanine in the triple decker and the particular oxidation state of the molecules i n the SAM (e.g., mono- vs. di- vs. tri- vs. tetracation). For all of the tr iple-decker SAMs, the charge-retention time monotonically increases as the oxidation state of the molecules in the SAM increases. Collectively, the st udies suggest that the triple-decker complexes are excellent candidates for multibit molecular information storage elements.