Design, synthesis, and characterization of prototypical multistate counters in three distinct architectures

The storage of multiple bits of information in distinct molecular oxidation states is anticipated to afford extraordinarily high memory densities. Among redox-active molecules, lanthanide porphyrinic triple-decker complexes are attractive candidates for such molecular information storage elements because they provide at least four cationic states over a modest potential range. Our approach toward a molecular multistate counter involves covalently linking two triple deckers with interleaving oxidation potentials to achieve a commensurate increase in the number of oxidation states within a single dyad. We report the design and synthesis of five dyads comprised of triple-decker complexes of the form (Pc) Ln( Pc) Ln( Por) or (Por(1))Ln( Pc) Ln( Por(2)), where Pc = phthalocyaninato, Por = porphyrinato, and Ln = Ce or Eu. The dyads were prepared in a modular building-block fashion by Pd-mediated coupling of an iodophenyl-triple decker and an ethynylphenyl-triple decker. The different dyad architectures examined include a vertical architecture with one linker (V1), a horizontal architecture with one linker (H1), and a horizontal architecture with two linkers (H2). In each dyad, one or two S-acetylthiomethyl groups incorporated on the porphyrinic moiety of the triple decker enables attachment to an electroactive surface via in situ cleavage of the protected thiol linker( s). Three dyads (Dyad1-3) have the V1 architecture but different compositions of triple deckers; three dyads (Dyad3-5) have identical composition but different architectures (V1, H1, H2) for comparison of the properties in self-assembled monolayers (SAMs) on gold. The SAM of each dyad exhibits robust reversible electrochemical behavior; the redox waves are essentially the sum of the waves of the component triple deckers. In contrast, mixtures of the component triple decker monomers form poor quality SAMs with inferior electrochemical characteristics. Accordingly, all three dyad architectures are viable constructs for assembling a multistate counter.