Design of Ru(II) Complexes Based on Anthraimidazoledione-Functionalized Terpyridine Ligand for Improvement of Room-Temperature Luminescence Characteristics and Recognition of Selective Anions: Experimental and DFT/TD-DFT Study

Abstract

In this work we report synthesis and characterization of three rigid and linear rodlike monometallic Ru(II) complexes based on a terpyridine ligand tightly connected to 9,10-anthraquinone electron-acceptor unit through phenyl-imidazole spacer. The motivation of designing these complexes is to enhance their excited-state lifetimes at room temperature. Interestingly it is found that all three complexes exhibit luminescence at room temperature with excited-state lifetimes in the range of 1.6-52.8 ns, depending upon the coligand as well as the solvent. Temperature-dependent luminescence investigations indicate that the energy gap between the emitting MLCT state and nonemitting metal-centered stateMC in the complexes increased enormously compared with parent [Ru(tpy)]. In addition, by taking advantage of the imidazole NH proton(s), which became appreciably acidic upon combined effect of electron accepting anthraquinone moiety as well as metal ion coordination, we also examined anion recognition and sensing behaviors of the complexes in organic, mixed aqueous-organic as well as in solid medium through different optical channels such as absorption, steady-state and time-resolved emission, and H NMR spectroscopic techniques. In conjunction with the experiment, computational investigation was also employed to examine the electronic structures of the complexes and accurate assignment of experimentally observed spectral and redox behaviors.

Ruthenium(II) Complexes with (3-Polyamino)phenanthrolines: Synthesis and Application in Sensing of Cu(II) Ions

“…In this work, we report on the synthesis of chemosensors bearing mixed ligand ([Ru(bpy)2(phen)] 2+ -type complexes as signaling groups. The stable and biocompatible ruthenium(II) tris(diimine) complexes (diimine = bpy, phen, terpyridine) have attracted considerable attention as luminophores and been explored in labeling, sensing, and imaging of various gases (dioxygen [5], nitric oxide [6], and carbon monoxide [7]), biological analytes (DNA, sugars, methylglyoxal, thiols, and amino acids) [8][9][10], and anions [11][12][13][14][15][16][17][18][19]. In contrast to most organic dyes, these complexes can exhibit a high brightness [20] in aqueous media, in part due to the electrostatic repulsive interactions that prevent the aggregation of these charged species in aqueous media.…”

Exploitation of the Second Coordination Sphere to Promote Significant Increase of Room-Temperature Luminescence Lifetime and Anion Sensing in Ruthenium–Terpyridine Complexes

“…As already mentioned, anion sensing behavior of several Ru(II) complexes based on polypyridyl−imidazole ligands were reported by different research groups. [45][46][47][48][58][59][60][61][62][63][64][65][66][67]69,70 Selected results are summarized in Table 5 for the sake of comparison in the context of the present study. It may be noted that among various Ru(II)-based chemosensors, only a few have the abilities to recognize CN − in water, and most of them can detect CN − either in nonaqueous solvent or in aqueous-organic medium with a low detection limit.…”

“…Most of these approaches were involved in modulating the energy of metal-to-ligand charge transfer ( 3 MLCT) and metal-centered ( 3 MC) states. Cyclometalated ligands have the ability to increase the energy of 3 MC state. − Change of the pyridine moiety by other heterocyclic rings sometimes produce less distorted octahedral geometry. − Important point is to extend electron delocalization in the excited state to minimize nonradiative deactivation channels. − During last few years, our group also designed a variety of Ru­(II)–terpyridine complexes by incorporating different aromatic and heteroaromatic moieties at the 4′-position of the terpyridine motif which are capable of displaying RT luminescence with reasonably long lifetimes. − …”

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors

“…This is mainly because the hydrogen bonding, electrostatic and Lewis acid-base interactions are significantly inhibited by the water molecules and other anions in the buffer solution [ 89 ]. This sub-section will discuss some examples of Ru(II) complex chemosensors for determination of anions in aqueous solution [ 90 – 92 ].…”