Perturbation of Charge-Transfer Complexes in Aqueous Solutions of PEG-DNB by Adding N-Ethylcarbazole and Li⁺ Cations

Abstract

Intramolecular charge-transfer (CT) complexation occurring in aqueous solutions of poly(ethylene glycol) monomethyl ether (PEG) capped at one end with a 3,5-dinitrobenzoyl (DNB) group was perturbed by compounds that interact with either the donor PEG chains or the acceptor DNB group. Hydrophobic N-ethylcarbazole (NEK) can be solubilized in aqueous solutions by the PEG-DNB complex surfactant. CT interactions between the NEK solute and the hydrophobic part of the surfactant, the DNB group, favor the solubilization process. The symmetric coplanar sandwich geometry of the NEK/DNB complex does not interfere with the PEG/DNB complex because of the sidewise orientation of the polyether chain. Thus, DNB forms complexes simultaneously with a π-electron donor, NEK, and a p-electron donor, PEG. An interesting consequence of the dual complex is the substantial increase in molecular weight resolution in the NMR spectra. Dissolving LiClO4 in aqueous solutions of PEG-DNB produces decomplexation. Li+ cations form ion−dipole interactions with PEG and remove it from its coiled complex with DNB.