Spectroscopic characterization of UV-induced efficient CO2 binding via non-covalent N···C interactions in N-containing PAH molecules

Abstract

This study investigates the molecular-level CO₂ binding of nitrogen-containing aromatic hydrocarbons, specifically 7-azaindole (7AI) and 2,7-diazaindole (27DAI). Using resonant two-photon ionization (R2PI), UV-UV hole-burning, and ion-dip infrared (IDIR) spectroscopy, we identified non-covalently bound molecular complexes, 7AI·CO₂ and 27DAI·(1,2)CO₂, formed in a supersonic molecular beam. The experimental results, supported by quantum chemical calculations, revealed that CO₂ binding in a 1 : 1 complex is facilitated by N⋯C non-covalent interactions and a weak N–H⋯O hydrogen bond interaction. The 27DAI·2CO₂ complex showed simultaneous binding of CO₂ at two different binding sites, while the mode of each CO₂ binding is aided by N⋯C and N–H⋯O interactions. The study highlights how nitrogen insertion into the aromatic framework and UV excitation significantly enhance CO₂ binding interactions, providing insights for designing next-generation CO₂ capture materials.