Counterpoise-corrected energies, NBO, HOMO–LUMO and interaction energies of poly(o-aminophenol) for ammonia sensing by DFT methods

• DFT and TD-DFT were employed for sensing properties of POAP and POAP+ toward NH3.
• Split valence basis set (6-31G*) is used for the simulation of all geometric and electronic properties.
• Greater interaction with NH3 was observed for the NH site of POAP as compared to O site.
• The study suggests better sensing properties of POAP for NH3 gas as compared to polyaniline.

The response of poly(o-aminophenol) (POAP) both in doped and undoped forms toward NH3 gas was investigated on the basis of density functional theory (DFT) at B3LYP and UB3LYP/6-31G* level of theory. POAP is unique due to the presence of two potential interactive sites, i.e., NH and O. The sensing ability of both of these interactive sites was investigated. Change in geometric parameters, and interaction energy analysis provide an effective evidence for the sensing ability of POAP for NH3 gas. Further support to the sensing response was obtained by natural bond orbital (NBO) and Mulliken charge analysis. Density of state spectra also show the interaction of NH3 with POAP and provide an understanding of the response mechanism of POAP toward NH3. Greater interaction was observed for the NH site of POAP as compared to O site, illustrating that NH site is the actual interactive site of POAP in both doped/undoped forms. The response became more sophisticated in the doped form of POAP.

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