American Chemical Society, Journal of the American Chemical Society, 2(137), p. 876-885, 2015
DOI: 10.1021/ja5111305
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We report the synthesis of a series of homologous oligoviologens in which different numbers of 4,4'-bipyridinium (BIPY2+) subunits are linked by p-xylylene bridges, as a prelude to investigating how their radical cationic forms self-assemble both in solution and in the solid state. The strong radical-radical interactions, which exist between the radical cationic forms of the BIPY2+ units ? namely, BIPY?+ ? in these oligoviologens, induces intra- or intermolecular folding of these homologues. UV/Vis/NIR Spectroscopic studies and DFT quantum mechanics indicate that the folding of the shorter oligoviologens is dominated by intermolecular radical-radical interactions. In addition to intermolecular interactions, strong intramolecular radical-radical interactions, which give rise to an NIR absorption band at 900 nm, tend to play a crucial role in governing the folding of the longer oligoviologens. The solid-state superstructure of the oligoviologen with three BIPY2+ units reveals that two intertwining chains fold together to form a dimer, stabilized by intermolecular radical-radical interactions. These dimers continue to stack in an infinite column through intermolecular radical-radical interactions between them. This research features an artificial biomimetic system which sustains delicate secondary and tertiary structures, reminiscent of those present in nucleic acids and proteins.