Robert J. Alvarado

Electroactive films incorporating 4,4′-Bipyridinium building blocks

Abstract The salts of 4,4′-bipyridinium dications are becoming the basic building blocks of an increasing number of electroactive materials and devices. These compounds (1) can be prepared in good yields starting from 4,4′-bipyridine, (2) undergo two consecutive and reversible reduction processes and (3) associate with electron rich substrates as a result of electrostatic and charge-transfer interactions. The unique combination of these attractive features has stimulated the identification of experimental protocols to assemble organized films of 4,4′-bipyridinium building blocks on electrode surfaces. Relying either on the Langmuir-Blodgett technique or on self-assembly processes, monolayers of 4,4′-bipyridinium derivatives and composite multilayers of these organic compounds and inorganic nanoparticles can be prepared on a variety of solid supports. The electroactive character of the 4,4′-bipyridinium dications facilitates the characterization of the resulting materials. In general, simple voltammetric measurements provide invaluable information on the structure and properties of the electroactive films. Furthermore, the electron accepting character of the organic building blocks and their recognition properties can be exploited to design simple devices able to execute specific functions. Indeed, displays, logic gates, photodiodes, rectifiers, sensors and switches have been implemented already relying on the careful design of 4,4′-bipyridinium building blocks and their ingenious integration in nanoscaled configurations.

Chemical retro-cyclopropanation reactions in methanofullerenes: effect of the 18-crown-6 moiety

Abstract Bulk electrolytic reduction efficiently removes certain methano addends from cyclopropanefullerenes. This retro-cyclopropanation reaction also takes place under chemical conditions by reaction with amalgamated magnesium in dry THF. The introduction of 18-crown-6 (18C6) results in considerably improved yields and in more reproducible results. For the cyclophane-type trans-1 fullerene-dibenzo [18] crown-6 conjugate (7) the retro-cyclopropanation reaction occurs efficiently when performed electrochemically and not at all when performed chemically. The electrochemical reaction is influenced by the presence of binding metal ions, which tend to stabilize the original compound after multiple electron reductions. These chemical reactions could be scaled-up to avoid the use of highly toxic HgBr2 to activate the magnesium.

First tether-directed regioselectivebis-functionalisation of C70: effects of cation complexation onthe redox properties of diastereoisomeric fullerene crown etherconjugates

The covalently templated bis-functionalisation of C70, employing a dibenzo-18-crown-6 tether, proceeds with complete regiospecificity and provides a bis-addition pattern which is disfavoured in sequential transformations.

Sandwiching C70 between two crown ether-bound cations: regioselective synthesis, electrochemistry and cation binding properties of C70 bis-crown ether conjugates

Tetrakis-adducts of C70, featuring two covalently attached crown ethers, form stable 1 ∶ 1 and 1 ∶ 2 host–guest complexes with alkali metal cations. A large influence of cation complexation on the first reduction potential of the fullerene was observed.