Carbon nanotube (CNT) fragments are exciting materials for the fields of supramolecular chemistry and nanotechnology. This is due to their tunable optical and physical properties, as well as their potential for host-guest chemical interactions. The authors from Boston and Drexel Universities and co-workers, report here for the first time, the synthesis of the radical cation of -cycloparaphenylene, prepared by reaction of -cycloparaphenylene with the oxidant triethyloxonium hexachloroantimonate (Et3O+SbCl6-). A vivid colour change, from yellow to orange to deep purple, accompanied the oxidation. The product remained stable when dry for several days, and was readily reduced back to -cycloparaphenylene on reaction with zinc dust.
Surprisingly, electron paramagnetic resonance (EPR) experiments on solutions of the radical cation, did not give detailed information, other than a characteristic signal for one unpaired electron. The material also proved difficult to crystallise in a pure form. Therefore, the focus shifted to photophysical, electrochemical and theoretical properties. As seen in the figure above, on the right, the radical cation of -cycloparaphenylene has two major absorptions at at 535 and 1115nm, which follow closely the values determined by density functional calculations (DFT), and are characteristically different to the parent neutral material.
Theoretical calculations also suggest a change to a highly delocalised structure in the radical cation and its dimer with the neutral compound, compared to benzene like character in -cycloparaphenylene. This should prove useful for potential applications in electronic and photovoltaic devices. Detailed results from computational studies on the electronic structures of the radical cation of -cycloparaphenylene (-CPP) and its resonance dimer, as well as the 6, 10 and 12 ring-containing ‘hoops’ are given. This article sheds valuable new light on the properties of intra- and inter-molecularly delocalised systems based on cycloparaphenylenes.
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Photophysical and theoretical investigations of the cycloparaphenylene radical cation and its charge-resonance dimer
Matthew R. Golder, Bryan M. Wong and Ramesh Jasti
Chem. Sci., 2013, Advance Article
Kevin Murnaghan is a guest web-writer for Chemical Science. He is currently a Research Chemist in the Adhesive Technologies Business Sector of Henkel AG & Co. KGaA, based in Düsseldorf, Germany. His research interests focus primarily on enabling chemistries and technologies for next generation adhesives and surface treatments. Any views expressed here are his personal ones and not those of Henkel AG & Co. KGaA.