Effect of fluorination on the adsorption properties of aromatic heterocycles toward methyl halides: A quantum chemical study

Despite the numerous publications describing the synthesis and electronic properties of fluorinated furan, thiophene and pyrrole, the systematic overview of their adsorption applications is still lacking. In this study, the effect of fluorination on the adsorption properties of furan (C₄H₄O), thiophene (C₄H₄S), pyrrole (C₄H₄NH) and benzene (C₆H₆) are investigated with the help of density functional theory (DFT) calculations. Herein, the adsorption energies of CH₃X (X = F, Cl & Br) on C₄H₄O, C₄H₄S, C₄H₄NH and C₆H₆ and their fluorinated analogues are calculated using ωB97XD/6-31+G(d, p) level of theory. The results of the adsorption energies and symmetry adapted perturbation theory (SAPT0) reveal that the adsorption affinity of adsorbent is enhanced upon fluorination due to the increasing dispersion forces. To comprehensively investigate the variation in the electronic properties of nonfluorinated and fluorinated systems, the HOMO, LUMO orbitals and NBO charges are analyzed. The isosurfaces of orbitals show that the electron density is more localized onto the fluorinated adsorbents which are probably due to the presence of multiple electronegative fluorine atoms. Owing to the electron-withdrawing nature of fluorine, the electronic charges are transferred from CH₃X to fluorinated adsorbents while the charges are shifted from nonfluorinated adsorbents to CH₃X. Furthermore, the TD-DFT calculations reveal that the electronic transition energies are significantly decreased in most of the fluorinated complexes especially, CH₃X@C₄F₄S and CH₃X@C₄F₄NH. With these findings, it can be postulated that fluorine substitution can significantly surge the electronic and adsorption properties of sensor materials.