Zn2+-Schiff’s Base Complex as an “On–Off-On” Molecular Switch and a Fluorescence Probe for Cu2+ and Ag+ Ions

Abstract

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of the Schiff's base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H 2 L) and its metal complexes with Zn 2+ , Cu 2+ and Ag + ions. The study aims to investigate the behavior of H 2 L and the binuclear Zn 2+ complex (1), as uorescent probes for the detection of metal ions (Zn 2+ , Cu 2+ and Ag + ) using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT). The six conformers of the H 2 L ligand were optimized using B3LYP/6-311++G** level of theory, while the L -2 -metal complexes were optimized by applying B3LYP functional with LANL2DZ/6-311++G** mixed basis set. The gas-phase and solvated Enol-cis isomer (E-cis) was found to be the most stable species. The absorption spectra of E-cis isomer and its metal complexes were simulated using B3LYP, CAM-B3LYP, M06-2X and ωB97X functionals with a 6-311++G** basis set for C, O, N and H atoms and LANL2DZ basis set for the metal ions (Zn 2+ , Cu 2+ and Ag + ). The computational results of B3LYP functional were in excellent agreement with the experimental ones. Hence, it has been adopted for performing the emission calculations. The results indicated that, the metal complex (1) can act as a uorescent chemosensor, for the detection of Ag + and Cu 2+ ions through the mechanism of the Intermolecular Charge Transfer (ICT) and as a molecular switch "On-Off-On" via the replacement of Cu 2+ by Ag + ions, as proved experimentally.

A multi-cation responsive Ni(ii)-supramolecular metallogel mimics a molecular keypad lockviareversible fluorescence switching

“…A fluorescent Zn(II)-complex comprising a Schiff base ligand showing "On-Off-On" reversible switching with chemical inputs of Ag + and Cu 2+ ions and serving as a sequence dependent molecular keypad lock was reported by Pandey et al 47 The said report was further supported by theoretical studies by other research groups. 48 Likewise, the present Ni(II)-metallogel (MG) exhibits reversible fluorescence 'Turn-OFF' in the presence of Cu 2+ /Hg 2+ and 'Turn-ON' with Zn 2+ , which enables MG also to act as a potential molecular keypad lock system. The reversibility and selectivity of MG toward Cu 2+ /Hg 2+ and Zn 2+ drove us to study the present system as a sequence dependent molecular keypad lock using the Cu 2+ , Hg 2+ and Zn 2+ ions as three different chemical inputs.…”

Mechanism of thermal oxidation into volatile compounds from (E)-4-decenal: A density functional theory study

“…In this study, all the reaction mechanism and related structures were calculated on Gussian16 software package ( Becke, 1992 , Becke, 1993 , Elroby, Banaser, & Aziz, 2022 , Fukui, 1981 , Shabani, Latina, & Li, 2020 , Yang and Lee., 1986 ). The Gibbs free energy was calculated by Shermo 2.0.8 program, and the accurate reaction potential energy surface was obtained ( Albaugh, Boateng, & Bradshaw, 2016 , Mahmoud, Shiroudi, & Abdel-Rahman, 2020 , Ryu, Park, & KiM, 2018 , Tian & Chen, 2021 ).…”

Density functional theory studies on the oleic acid thermal oxidation into volatile compounds

“…All calculations in this study were done on the Gussian16 software package ( Müller, Shabani, Wagenpfeil, & Vogt, 2021 , Shabani et al, 2020 ). Geometry optimizations for the molecular ions, intermediates, and fragments were carried out at the unrestricted B3LYP (UB3LYP) density functional levels of theory using the 6-311G (d, p) basis set ( Elroby et al, 2022 , Pedersen and Mikkelsen, 2022 ). Transition state (TS) geometries connecting the stable structures were searched at the same level.…”