Noncovalent C···N Interaction to Capture CO₂ on a Neutral Aromatic Molecule in the Gas Phase: Experimental Determination of the UV-Induced Adsorption Energy

This work describes a novel experimental method to determine the adsorption energy of a molecular complex in the ground and excited states. An increased CO₂ capture efficiency was obtained upon electronic excitation of nitrogen-containing heterocycles, due to the formation of strong C···N noncovalent interaction. We performed a combined experimental and computational investigations, to understand the noncovalent interaction between carbon dioxide (CO₂) and 2-(2'-pyridyl)benzimidazole (PBI) in the gas phase. Using R2PI, UV-UV hole burning, and IDIR spectroscopic technique, we characterized the PBI-CO₂ complex. The S₀ → S₁ origin band of the PBI-CO₂ complex was red-shifted by 329 cm^-1 relative to that of the PBI monomer, indicating that the PBI-CO₂ complex become more stable upon UV absorption. Therefore, the adsorption energy of CO₂ on PBI increased by nearly 30% upon electronic excitation due to the higher stability of the complex in the excited state, which was bound to the adsorbent mainly via the C···N interaction.