Octulene: A Hyperbolic Molecular Belt that Binds Chloride Anions

Abstract

Octulene, the higher homologue of kekulene and septulene, was synthesized using the fold-in method. This new hydrocarbon macrocycle contains a large 24-membered inner circuit, which is peripherally fused to 24 benzene rings. Such an arrangement produces considerable hyperbolic distortion of the π-conjugated surface. The consequences of distortion in octulene were explored using photophysical methods, which revealed a reduced electronic band gap and greater flexibility of the π system. Octulene contains a functional cavity with a diameter larger than 5.5 Å that is capable of efficiently binding the chloride anion in a nonpolar solvent (K_a = 2.2(4)×10⁴ m^-1 , 1 % dichloromethane (DCM) in benzene). The octulene-chloride interaction is stabilized by eight weak C(sp² )H⋅⋅⋅Cl bonds, providing the first example of a hydrocarbon-based anion receptor.

Keywords: anion binding; aromaticity; hydrocarbons; organic synthesis; photophysics.