N‐heterocyclic carbene (NHC) boosted photoluminescence: Synthesis, structures, and photophysical properties of bpy/phen‐Au(III)‐NHC complexes

Abstract

Herein, we first present synthesis, structures, luminescent properties, and electrochemistry of gold(III)‐N‐heterocyclic carbene (NHC) complexes fasten with 2,2′‐bipyridine (bpy) or 1,10′‐phenanthroline (phen). Starting from the proligand 3‐[pyridin‐3‐yl]imidazo[1,5‐a]pyridin‐4‐ylium hexafluorophosphate (1·HPF6), two novel complexes, namely, [Au(1)(bpy)Cl][PF6]2 (2) and [Au(1)2(phen)][PF6]3 (3), have been synthesized and characterized by several spectroscopic techniques. Finally, the solid‐state structures of 2, 3, and precursors [Au(bpy)Cl2][PF6] and [Au(phen)Cl2][PF6] have been determined by single‐crystal X‐ray diffraction studies. The absorption, emission, and lifetime properties of 2 and 3 have been compared with the precursors [Au(bpy)Cl2][PF6] and [Au(phen)Cl2][PF6] to observe the influence of NHC. Though the precursors [Au(bpy)Cl2][PF6] and [Au(phen)Cl2][PF6] are non‐luminescent, yet complexes 2 and 3 are luminescent. A combination of the chromophoric and π‐acid bpy/phen ligand in Au(III) complexes with the strong σ‐donor NHC ligand significantly enhanced the emission properties of the complexes. The blue emission of 2 and 3 in 390–500 nm regions has been tentatively ascribed to arise from intraligand and metal‐to‐ligand charge transfer (MLCT) transitions; also, partial contributions are expected from hydrogen‐bonding interactions. Cyclic voltammetric studies revealed Au(III) → Au(I) and Au(I) → Au(0) reductions at ~ −0.35 to ‐0.29 V and ~ −1.20 to ‐1.15 V, and the potentials are compared with precursors.

[AuIII(N^N)Br2](PF6): A Class of Antibacterial and Antibiofilm Complexes (N^N = 2,2′-Bipyridine and 1,10-Phenanthroline Derivatives)

“…The crystal structures of compounds 1 , 2 , 4 , and 5 ·CH 2 Cl 2 (Table S1), as well as those obtained for compounds 6 and 9 (confirming the previously reported crystallographic data), , show the central gold­(III) ion lying in a slightly distorted square-planar coordination environment. The complex cations [Au­(N^N)­Br 2 ] + are almost planar, with the exception of the phenyl substituents at the 1,10-phenanthroline ligand in 5 ·CH 2 Cl 2 (Figures , S4, and S5).…”

“…The complex cations [Au(N^N)Br 2 ] + are almost planar, with the exception of the phenyl substituents at the 1,10-phenanthroline ligand in 5 ·CH 2 Cl 2 ( Figures 1 , S4 , and S5 ). The average Au–Cl (2.265 and 2.254 Å for 6 and 9 , respectively) and Au–Br distances (2.383, 2.377, 2.383, and 2.377 Å for 1 , 2 , 4 , and 5 ·CH 2 Cl 2 , respectively) are similar to those reported for analogous [Au(N^N)X 2 ] + complexes ( Tables S2 and S3 ) 42 , 48 , 50 − 55 and show the expected increase of d Au–X on passing from X = Cl to X = Br. In all structures, the packing is mainly governed by contacts between complex cations and hexafluorophosphate anions ( Figure S6 for 4 ).…”

“…Antimicrobial tests against Gram-positive (Staphylococcus aureus and Streptococcus intermedius) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria were carried out on compounds 1 – 4 and 6 – 9 and the corresponding N^N free ligands (Table ), while compounds 5 and 10 were not assayed for solubility reasons. It is worth mentioning that a systematic study on the antibacterial activity of these systems has never been carried out, although some studies were conducted on the biological activity of compounds 6 – 10 , ,,,− and the antimicrobial properties of related [Au­(N^N)­Cl 2 ] + systems with different diimine ligands and counteranions were occasionally investigated. ,− …”

“…Compounds 6 and 9 were prepared as previously reported. ,, Compounds 7 , 8 , and 10 were synthesized by adapting previously reported procedures. − …”

Therapeutic potential of Ag(i)–, Au(i)–, and Au(iii)–NHC complexes of 3-pyridyl wingtip N-heterocyclic carbenes (NHCs) against lung cancer

“…The precursor 3-[(pyridin-3-yl)]imidazo[1,5- a ]pyridin-4-ylium hexafluorophosphate, 1 ·HPF 6 , was prepared using the Schiff base 3-pyridyl- N -(2 pyridyl)methylamine, as described by our group. 28…”