Theoretical study of the reactivity of oligo-pyrrole derivatives linked at their ends to the Magnesol, Ferrol, and Zinkol fragments: NBO, DFT, and TD-DFT calculations

Context

This study compares the electronic and structural properties of oligopyrroles (OPn) grafted with metal rings (Magnesol OPnMg, Ferrol OPnFe, and Zinkol OPnZn) with those of standard oligopyrroles (OPn). In the context of the polymerization of oligomers from n = 1 to n = 15, the parameters of global reactivity and excited states obey exponential equations (ƒ(x) = A + B Exp^−R(x)), allowing values to be predicted to infinity. The corresponding infinity results reveal that energy gaps (ΔE_H-L) vary between 3.14 and 5.20 eV, while chemical hardnesses (η) oscillate between 1.507 and 2.60 eV, with overall electrophilicity (ω) and nucleophilicity (Nu) of 0.74–1.40 eV and 5.47–5.53 eV, respectively. The new oligopyrrole derivatives show increases in intramolecular charge transfer (ICT) and UV–Vis absorptions in the violet (λ_max between 407 and 431 nm). NBO analysis shows a reduction in hydrogen charges in the –NH groups of oligopyrroles based on metal derivatives, enhancing their nucleophilicity. In addition, these molecules display better solubility, with favorable solvation energies (ΔG_solv) (24–35 kcal-mol⁻¹) compared to OPn. Finally, metal-based derivatives show stronger interactions with formaldehyde (HCHO) in aqueous media than OPn, demonstrating interaction energy differences (E_int) ranging from 0.7 to 1.40 kcal-mol⁻¹.

Methods

All calculations were performed using the Gaussian 16 program. The selected functionals are: B3LYP, CAM–BLYP, B3LYP–D3, CAM–BLYP–D3, and TD–CAM–BLYP. The basis–sets used are: 6–31 +  + G(d,p) and LanL2DZ. Finally, the natural bond orbital (NBO) method was used in this study.