Viologen–Cycloparaphenylene Hybrids: Luminescent Molecular Nanocarbons for Anion Binding and Specific Vapor Sorption†

Two viologen-like macrocyclic receptors, [1]2+ and [2]2+, merging a bent oligophenylene loop with a (para-xylylene)bispyridinium moiety were designed and synthesized. Both dications were derived from the same precursor: the more strained cycloparaphenylene analogue [1]2+ was obtained using a reductive aromatization, whereas the less curved, meta-phenylene-containing [2]2+ was generated using a double eliminative rearrangement. [1]2+ is active as a receptor toward pyrene-1,3,6,8-tetrasulfonate, displaying a 2:1 binding interaction, with K11 = 7.4(3) × 103 M–1. In the solid state, [1][TFA]2 shows differential sorption of C6 hydrocarbons and shows reversible sorption of water. [1]2+ displays yellow emission in solution (λmaxem = 544 nm in DMF), which is considerably red shifted in the solid state (λmaxem = 644 nm for dry samples). Both [1]2+ and [2]2+ undergo electrochemical reduction, yielding transient viologen-like radical cations and diradicals.