Computational investigation on the molecular and electronic structure of the interaction of thiophene with various toxic gases

Density functional theory calculations were used to examine adsorption of carbonyl fluoride (COF₂), cyanogen chloride (CNCl), and boron trifluoride (BF₃) on thiophene using B3LYP/6-31+G(d) and ωB97XD/6-31+G(d). All complexes exhibit weak exothermic adsorption consistent with physisorption. Counterpoise-corrected interaction energies at B3LYP are −2.259, −3.389, and −4.730 kJ/mol for COF₂, CNCl, and BF₃, respectively; corresponding ωB97XD values are −11.970, −10.042, and −16.736 kJ/mol. Adsorption changes the dipole moment of thiophene from 0.5469 D to 1.2527, 3.4267, and 0.6534 D, respectively. COF₂ reduces the calculated HOMO–LUMO gap from 5.97 to 5.131 eV, whereas CNCl and BF₃ yield gaps of 5.972 and 6.00 eV. Mulliken and natural bond orbital analyses indicate small intermolecular charge transfers, and the calculated desorption times are short under the assumed conditions. BF₃ has the strongest calculated binding, while COF₂ produces the largest orbital-gap response. These molecular-level predictions support further investigation of thiophene-based materials for toxic-gas sensing, although device performance requires experimental validation. KEY WORDS: Thiophene, Toxic gases, Density functional theory, Interaction energy, Charge transfer, Molecular orbitals Bull. Chem. Soc. Ethiop. 2027, 41(1), 219-238. DOI: https://dx.doi.org/10.4314/bcse.v41i1.15