A Novel Homoconjugated Propellane Triimide: Synthesis, Structural Analyses, and Gas Separation

Rigid three-dimensional (3D) polycyclic propellanes have garnered interest due to their unique conformational spaces, which display great potential use in selectivity, separation and as models to study through-space electronic interactions. Herein we report the synthesis of a novel rigid propellane, trinaphtho[3.3.3]propellane triimide, which comprises three imide groups embedded on a trinaphtho[3.3.3]propellane. This propellane triimide exhibits large bathochromic shift, amplified molar absorptivity, enhanced fluorescence, and lower reduction potential when compared to the subunits. Computational and experimental studies reveal that the effective through-space π-orbitals interacting (homoconjugation) occurs between the subunits. Single-crystal XRD analysis reveals that the propellane triimide has a highly quasi-D3h symmetric skeleton and readily crystallizes into different superstructures by changing alkyl chains at the imide positions. In particular, the porous 3D superstructure with S-shaped channels is promising for taking up ethane (C2H6) with very good selectivity over ethylene (C2H4), which can purify C2H4 from C2H6/C2H4 in a single separation step. This work showcases a new class of rare 3D polycyclic propellane with intriguing electronic and supramolecular properties.