A theoretical and electrochemical impedance spectroscopy study of the adsorption and sensing of selected metal ions by 4-morpholino-7-nitrobenzofuran.

The selectivity of a novel chemosensor, based on a modified nitrobenzofurazan referred to as NBD-Morph, has been investigated for the detection of heavy metal cations (Co2+, Pb2+, Mg2+, Ag+, Cu2+, Hg2+, Ni2+, and Zn2+). The ligand, 4-morpholino-7-nitrobenzofurazan (NBD-Morph), was characterized using spectroscopic techniques including FT-IR and 1H NMR. Vibrational frequencies obtained from FT-IR and proton NMR (1H) chemical shifts were accurately predicted employing the density functional theory (DFT) at the B3LYP level of theory. Furthermore, an examination of the structural, electronic, and quantum chemical properties was conducted and discussed. DFT calculations were employed to explore the complex formation ability of the NBD-Morph ligand with Co2+, Pb2+, Mg2+, Ag+, Cu2+, Hg2+, Ni2+, and Zn2+ metal cations. The comparison of adsorption energies for all possible conformations reveals that NBD-Morph exhibits sensitivity and selectivity towards metal ions, including Pb2+, Cu2+, Ag+, and Ni2+. However, an assessment of their reactivity using QTAIM topological parameters demonstrated the ligand's greater complexation ability toward Cu2+ or Ni2+ than those formed by Pb2+ or Ag+. Additionally, molecular electrostatic potential (MEP), Hirshfeld surfaces, and their associated 2D-fingerprint plots were applied to a detailed study of the inter-molecular interactions in NBD-Morph-X (X = Pb2+, Cu2+, Ag+, Ni2+) complexes. The electron localization function (ELF) and the localized-orbital locator (LOL) were generated to investigate the charge transfer and donor-acceptor interactions within the complexes. Electrochemical analysis further corroborates the theoretical findings, supporting the prediction of NBD-Morph's sensory ability towards Ni2+ metal cations. In conclusion, NBD-Morph stands out as a promising sensor for Ni2+.

Exploration of intramolecular charge transfer in para-substituted nitrobenzofurazan: Experimental and theoretical analyses.

The present work aims at exploring the high electrophilic character of 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) toward the morpholine group by an SNAr reaction in acetonitrile or water (thereafter referred to as NBD-Morph). The electron-donating ability of the morpholine causes intra-molecular charge transfer (ICT). In this report, we present a comprehensive study on the optical characteristics using UV-Vis, photoluminescence (cw-PL) and its time-resolved (TR-PL) to determine the properties of the emissive intramolecular charge transfer (ICT) in the NBD-Morph donor-acceptor system. An exhaustive theoretical investigation utilizing the density functional theory (DFT) and its extension TD-DFT methods is an essential complement of experiments to rationalize and understand the molecular structure and related properties. The findings from QTAIM, ELF, and RDG analyses establish that the bonding between morpholine and NBD moieties is of the electrostatic or hydrogen bond type. In addition, the Hirshfeld surfaces have been established to explore the types of interactions. Further, the non-linear optical (NLO) responses of the compound have been examined. The structure-property relationships obtained through the combined experimental and theoretical offer valuable insights for designing efficient NLO material.

Sensor based on redox conjugated poly(para-phenylene) for the simultaneous detection of dopamine, ascorbic acid, and uric acid in human serum sample.

An electrochemical sensor for the individual and the simultaneous detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA) based on redox conjugated "poly(para-phenylene)" (Fc-ac-PPP) bearing ferrocene and carboxylic acid in lateral position has been developed. The electrochemical characterization of the sensor has been studied with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry (CA). We highlighted that the catalytic activity of the Fc-ac-PPP polymer provided by its redox electrochemical properties and chemical structure allows the electrochemical detection of DA, AA, and UA. We demonstrated that the sensor provides high sensitivity and selective signal in the coexistence of DA, AA, and UA within a short time. Low detection limits and wide linear ranges of detection have been demonstrated respectively for DA 3 × 10-10 M (1 nM-10 µM), AA 1.6 × 10-8 M (0.1 µM-1 mM), and UA 1 × 10-8 M (0.1 µM-1 mM). In addition, the sensor has been successfully applied to determine DA in urine and human serum samples even in the presence of high concentrations of AA and UA. This sensor could be a powerful device for the detection of other electroactive compounds thanks to its high catalytic properties and chemical structure. Graphical abstract.