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 (H
2
L) and its metal complexes with Zn
2+
, Cu
2+
and Ag
+
ions. This study aims to investigate the behavior of H
2
L and the binuclear Zn
2+
complex (
1
) as fluorescent 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 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 (Zn
2+
, Cu
2+
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 Cu
2+
ions through the mechanism of intermolecular charge transfer (ICT) and as a molecular switch “On–Off-On” via the replacement of Cu
2+
by Ag
+
ions, as proved experimentally.