Cyclometalated rhodium and iridium complexes with imidazole containing Schiff bases: Synthesis, structure and cellular imaging

Abstract

Cyclometalated rhodium(III) and iridium(III) complexes (1–4) of two Schiff base ligands L1 and L2 with the general formula [M(ppy)2(Ln)]Cl {M = Rh, Ir; ppy = 2-phenylpyridine; n = 1, 2; L = Schiff base ligand} have been synthesized. The new ligands and the complexes have been characterized with spectroscopic techniques. Electrochemistry of the complexes revealed anodic behavior, corresponding to an M(III) to M(IV) oxidation. The X-ray crystal structures of complexes 2 and 4 have also been determined to interpret the coordination behavior of the complexes. Photophysical study shows that all the complexes display fluorescence at room temperature with quantum yield of about 3 × 10–2 to 5 × 10−2. The electronic absorption spectra of all the complexes fit well with the computational studies. Cellular imaging studies were done with the newly synthesized complexes. To the best of our knowledge, this is the first report of organometallic complexes of rhodium(III) and iridium(III) with Schiff base ligands explored for cellular imaging. Emphasis of this work lies on the structural features, photophysical behavior, cellular uptake and imaging of the fluorescent transition metal complexes.

Self-assembled supramolecular structures of O,N,N′ tridentate imidazole–phenol Schiff base compounds

“…1 This ease of synthesis coupled with the ubiquitous nature of imidazole moieties in enzymes, proteins and pharmaceuticals render it a favourable choice in biological studies. 1,2 Additionally, Schiff base ligands are able to coordinate and stabilise metals in a wide range of oxidation states. [2][3][4][5][6][7][8] Metal complexes of imidazole-based Schiff base ligands have therefore found application in a wide variety of elds including medicinal and biological chemistry as well as catalysis.…”

“…1,2 Additionally, Schiff base ligands are able to coordinate and stabilise metals in a wide range of oxidation states. [2][3][4][5][6][7][8] Metal complexes of imidazole-based Schiff base ligands have therefore found application in a wide variety of elds including medicinal and biological chemistry as well as catalysis. 1 In recent years, derivatives of the 1-methyl-imidazol-2-yl methylidine Schiff Base ligand have been co-ordinated to various metals for a wide variety of applications.…”

“…18 In biological applications, the N,N 0 ,N 00 tridentate ligand (f) has been coordinated to Cu(II) for purposes of creating novel anticancer chemotherapeutic agents, 19 while Ir(III) and Rh(III) uorescent complexes of ligand (g) can be used as bioimaging probes. 2 Imidazole Schiff bases have also been used in enzyme modelling, such as the use of a trinuclear manganese complex containing ligand (h). 20 A few N-H imidazole derivatives of ligand (h) have also been reported as free ligands and coordinated to various metal ions including, but not limited to, Fe(III), Ni(II) and Cd(II).…”

Spectroscopic and theoretical characterization of 2-(4-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-oxide

“…Soft systems are large and highly polarisable, while hard systems are relatively small and much less polarisable. Mandal et al[75] reported the cyclometalated rhodium and iridium complexes with imidazole containing Schiff bases and the HOMO, LUMO values are 48.73 and 16.21 eV for iridium complexes and 49.02 and 16.78 eV, rhodium complexes with imidazoles.…”

Phosphorescence “Turn‐On” Sensing of Anions by Rhenium(I) Schiff‐Base Complexes

“…Guo and Velmathi developed a fluorescent turn‐on recognition of anions by the intermolecular hydrogen bond inhibited C=N isomerization mechanism. Although these Schiff‐base compounds are widely used because of their facile synthesis, remarkable versatility, strong coordination abilities and good solubility in common solvents, their short fluorescence wavelength, short lifetime and low quantum yield make them more complicated especially in live cell imaging where these chromophores result from photobleaching and loss of signal …”