Zn2+-Schiff's Base Complex as an "On-Off-On" Molecular Switch and a Fluorescence Probe for Cu2+ and Ag+ Ions

Shaaban A Elroby; Bashair Abdullah Banaser; Saadullah G Aziz; Abdesslem Jedidi; Walid I Hassan; Osman I Osman

doi:10.1007/s10895-021-02864-4

Zn²⁺-Schiff's Base Complex as an "On-Off-On" Molecular Switch and a Fluorescence Probe for Cu²⁺ and Ag⁺ Ions

J Fluoresc. 2022 Mar;32(2):691-705. doi: 10.1007/s10895-021-02864-4. Epub 2022 Jan 18.

Authors

Shaaban A Elroby^{1

2}, Bashair Abdullah Banaser³, Saadullah G Aziz⁴, Abdesslem Jedidi⁴, Walid I Hassan⁴, Osman I Osman^{4

5}

Affiliations

¹ Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia. skamel@kau.edu.sa.
² Chemistry Department, Faculty of Science, Beni-Suef University, Beni-Suef, 62511, Egypt. skamel@kau.edu.sa.
³ Chemistry Department, Faculty of Science, Taif University, Turabah, 29731, Saudi Arabia. bbanasr@stu.kau.edu.sa.
⁴ Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia.
⁵ Chemistry Department, Faculty of Science, University of Khartoum, P.O. Box 321, Khartoum, 11111, Sudan.

PMID: 35040031
DOI: 10.1007/s10895-021-02864-4

Abstract

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of Schiff's base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H₂L) and its metal complexes with Zn²⁺, Cu²⁺ and Ag⁺ ions. This study aims to investigate the behavior of H₂L and the binuclear Zn²⁺ complex (1) as fluorescent probes for the detection of metal ions (Zn²⁺, Cu²⁺ and Ag⁺) using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The six conformers of the H₂L ligand were optimized using the B3LYP/6-311 + + G** level of theory, while the L^-2-metal complexes were optimized by applying the B3LYP functional with the 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 the 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 a LANL2DZ basis set for the metal ions (Zn²⁺, Cu²⁺ and Ag⁺). The computational results of the B3LYP functional were in excellent agreement with the experimental results. Hence, it was adopted for performing the emission calculations. The results indicated that metal complex (1) can act as a fluorescent chemosensor for the detection of Ag⁺ and Cu²⁺ ions through the mechanism of intermolecular charge transfer (ICT) and as a molecular switch "On-Off-On" via the replacement of Cu²⁺ by Ag⁺ ions, as proved experimentally.

Keywords: Density functional theory (DFT) and time-dependent density functional theory (TDDFT); Fluorescence probe molecular switch; Photoinduced electron transfer (PET); Schiff base.