Abstract
A series of different substituted terpyridine (tpy)-based ligands have been synthesized by Kröhnke method. Their binding behaviour was evaluated by complexing them with Co(II), Fe(II) and Zn(II) ions, which resulted in interesting coordination compounds with formulae, [Zn(tpy)2]PF6, [Co(tpy)2](PF6)2, [Fe(tpy)2](PF6)2 and interesting spectroscopic properties. Their absorption and emission behaviours in dilute solutions were investigated in order to explain structure–property associations and demonstrate the impact of different aryl substituents on the terpyridine scaffold as well as the role of the metal on the complexes. Photo-luminescence analysis of the complexes in acetonitrile solution revealed a transition from hypsochromic to bathochromic shift. All the compounds displayed remarkable photo-luminescent properties and various maximum emission peaks owing to the different nature of the functional groups. Furthermore, the anti-microbial potential of ligands and complexes was evaluated with docking analyses carried out to investigate the binding affinity of terpyridine-based ligands along with corresponding proteins (shikimate dehydrogenase and penicillin-binding protein) binding sites. To obtain further insight into molecular orbital distributions and spectroscopic properties, density functional theory calculations were performed for representative complexes. The photophysical activity and interactions between chromophore structure and properties were both investigated experimentally as well as theoretically.
Highlights
2,20:60,200-Terpyridine is a tridentate ligand which contains three coordination sites belonging to N-heteroaromatic rings and constitutes a significant class of aromatic heterocyclic compounds
Our preliminary study focused on the synthesis of different 6,600 symmetrically substituted 40-aryl-2,20:60,200-terpyridine substrates
The chemical structures of all the ligands were corroborated by UV-Vis, FTIR and NMR spectroscopies. These ligands were coordinated with the transition metal cations Fe2+, Co2+, Zn2+ to produce the desired complexes (C1–C27) in very good yields. These complexes were prepared by the reaction of the terpyridine ligands with the metal salts in a 2 : 1 molar ratio in dichloromethane (DCM) and purified by washing with ethanol
Summary
2,20:60,200-Terpyridine is a tridentate ligand which contains three coordination sites belonging to N-heteroaromatic rings (figure 1) and constitutes a significant class of aromatic heterocyclic compounds. Terpyridine motifs and their complexes have attracted the increasing attention of materials chemists due to their applications in several fields, for instance photovoltaic devices, DNA binders, sensors, photosensitizers, molecular chemistry, medicinal chemistry and metal-organic framework (MOF) construction [1–3] Their complexes with transition metals, in particular, can lead to unique photo-luminescence, catalysis, sensor properties and quite promising tumour-inhibiting activities [4–19]. Constable’s group has thoroughly studied the synthesis of terpyridine derivatives, and a wide variety of substituted terpyridine ligands were prepared in high yields through the Kröhnke reaction by condensation of 2-acetylpyridine with various substituted aryl aldehydes followed by oxidation in simple and effective processes [20–25] These ligands show unique coordinative capabilities towards transition elements and have received much attention recently because of their varied/extensive uses in diverse research fields extending from therapeutic uses (such as anti-cancer and DNA intercalation) to material sciences ( photovoltaics, sensitizers) and catalysis [26]. We have established a detailed structure–activity relationship (SAR) between these architectures and their biological and spectrophotometric properties
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