Viologen–cycloparaphenylene hybrids: luminescent molecular nanocarbons for anion binding and specific vapor sorption

Abstract

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 (λ^em_max = 544 nm in DMF), which is considerably red shifted in the solid state (λ^em_max = 644 nm for dry samples). Both [1]²⁺ and [2]²⁺ undergo electrochemical reduction, yielding transient viologen-like radical cations and diradicals.