N···CO n → π Interaction: Gas-Phase Electronic and Vibrational Spectroscopy Combined with Quantum Chemistry Calculations

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 128; no. 23; pp. 4685 - 4693
• Main Authors: Panwaria, Prakash, Das, Aloke
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13-06-2024
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215; 1520-5215
• DOI: 10.1021/acs.jpca.4c02181

Herein, we have used gas-phase electronic and vibrational spectroscopic techniques for the first time to study the N···CO n → π* interaction in ethyl 2-(2-(dimethylamino) phenyl) acetate (NMe2-Ph-EA). We have measured the electronic spectra of NMe2-Ph-EA in the mass channels of its two distinct fragments of m/z = 15 and 192 using a resonant two-photon ionization technique as there was extensive photofragmentation of NMe2-Ph-EA. Identical electronic spectra obtained in the mass channels of both fragments confirm the dissociation of NMe2-Ph-EA in the ionic state, and hence, the electronic spectrum of the fragment represents that of NMe2-Ph-EA only. UV–UV hole-burning spectroscopy proved the presence of a single conformer of NMe2-Ph-EA in the experiment. Detailed quantum chemistry calculations reveal the existence of a N···CO n → π* interaction in all six low-energy conformers of NMe2-Ph-EA. A comparison of the IR spectrum of NMe2-Ph-EA acquired from the gas-phase experiment with those obtained from theoretical calculations indicates that the experimentally observed conformer has a N···CO n → π* interaction. The present finding might be further valuable in drug design and their recognition based on the N···CO n → π* interaction.