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

A novel homoconjugated propellane comprising three imide groups embedded on a trinaphtho[3.3.3]propellane, has been synthesized and characterized. This rigid propellane triimide is featured with large bathochromic shift, intense luminescence, amplified molar absorptivity, and lower reduction potential relative to the subunits. The propellane triimide readily crystallizes into porous 3D superstructure, which is promising for C₂H₆/C₂H₄ separation.

Abstract

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-D _3h 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.

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