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Abstract
The present article presents a comprehensive laser spectroscopic characterization of 2-(2′-Pyridyl)-Benzimidazole (PBI)-S1,2 complexes (S = H2O, CH3OH, and NH3) isolated in the gas phase. The study aimed to understand docking preference of small molecules on N-bearing bio-relavent multifunctional molecules. Based on the LIF and R2PI spectroscopy, we have identified two distinct isomers of 1:1 (PBI-H2O) and 1:2 (PBI-(H2O)2) complexes. In the cases of PBI-CH3OH and PBI-NH3 systems, a single 1:1 and 1:2 complex was identified in each case. Computational analyses predicted the most stable structure, labelled as PBI-S-a with NIH···S and SH···NP (NIH = imidazolyl NH and NP: Pyridyl-N) hydrogen bonds at site-a. The structures were associated with significantly higher stability of the S1 state (D0(S1)>D0(S0)) compared to that in the corresponding ground states. The structure of PBI-H2O-b isomer, with CPH···S and SH···NI hydrogen bonds, was characterized by a blue-shifted band origin transition, validating computational predictions. The PBI-(S)2-aa (S=H2O, CH3OH, and NH3) isomers exhibited large red-shifted S0→S1 band origins, as predicted computationally. A unique PBI-(H2O)2-ab isomer was detected with a significantly lowered redshifted band origin transition compared to the aa-isomer, in which a solvent molecule is bound to the sites a and b PBI molecule. Notably, PBI-H2O complexes exhibit solvent-to-chromophore proton transfer reactions, with varying energy barriers depending on the isomeric configuration. The energy barriers for proton transfer reactions in PBI-H2O-b isomers demonstrated significantly elevated barriers (> 800 cm-1). In PBI-(H2O)-aa, the energy barrier (>436 cm-1) is marginally elevated from 420±10 cm-1 in PBI-H2O-a isomer. This study enhances the understanding of complex molecular interactions and provides insights into the excited-state processes, laying the groundwork for further investigations.
Supplementary materials
Title
Spectroscopic Characterization of the Complexes of 2-(2′-Pyridyl)-Benzimidazole and (H2O)1,2, (CH3OH)1,2, and (NH3)1,2 Isolated in the Gas Phase
Description
The present article presents a comprehensive laser spectroscopic characterization of 2-(2′-Pyridyl)-Benzimidazole (PBI)-S1,2 complexes (S = H2O, CH3OH, and NH3) isolated in the gas phase. The study aimed to understand docking preference of small molecules on N-bearing bio-relavent multifunctional molecules. Based on the LIF and R2PI spectroscopy, we have identified two distinct isomers of 1:1 (PBI-H2O) and 1:2 (PBI-(H2O)2) complexes. In the cases of PBI-CH3OH and PBI-NH3 systems, a single 1:1 and 1:2 complex was identified in each case. Computational analyses predicted the most stable structure, labelled as PBI-S-a with NIH···S and SH···NP (NIH = imidazolyl NH and NP: Pyridyl-N) hydrogen bonds at site-a. The structures were associated with significantly higher stability of the S1 state (D0(S1)>D0(S0)) compared to that in the corresponding ground states. The structure of PBI-H2O-b isomer, with CPH···S and SH···NI hydrogen bonds, was characterized by a blue-shifted band origin transition, validating computational predictions.
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