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Sengottuvelan, Nallathambi,Yun, Seong-Jae,Kang, Sung-Kwon,Kim, Young-Inn Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.12
A new series of heteroleptic cyclometalated iridium(III) complexes has been synthesized and characterized by absorption, emission and cyclic voltammetry studies: $(pqx)_2Ir(acac)$ (1), $(dmpqx)_2Ir(acac)$ (2) and $(dfpqx)_2Ir(acac)$ (3) where pqx=2-phenylquinoxalinate, dmpqx=2-(2,4-dimethoxyphenyl)quinoxalinate, dfpqx=2-(2,4-difluorophenyl) quinoxalinate and acac=acetylacetonate anion. The reaction of excess acetylacetone with ${\mu}$-chloride-bridged dimeric iridium complex, $[(C\^N)_2Ir({\mu}-Cl)]_2$, gives a complex 1 and an unusual hydridoiridium(III) complex, $(pqx)IrH(acac)_2$ (4). The complex 1, 2 and 3 show their emissions in an orangered region (${\lambda}_{PL,max}$ = 583-616 nm), and the emission maxima can be tuned by the change of substituent at phenyl ring of 2-phenylquinoxaline ligand. The phosphorescent line shape indicates that the emissions originate predominantly from $^3MLCT$ states with little admixture of ligand-based $^3({\pi}-{\pi}^*)$ excited states. The structures of complex 3 and 4 are additionally characterized by a single crystal X-ray diffraction method. The complex 3 shows a distorted octahedral geometry around iridium(III) metal ion. A strong trans influence of the phenyl ring is examined. In complex 4, there are two discrete molecules which are mirror images each other at the ratio of 1:1 in an unit cell. We propose that the phosphorescent complex 1, 2 and 3 are possible candidates for the phosphors in OLEDs applications.
Sengottuvelan, Nallathambi,Yun, Seong-Jae,Kim, Dae-Young,Hwang, In-Hye,Kang, Sung Kwon,Kim, Young-Inn Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.1
A series of highly efficient red phosphorescent heteroleptic iridium(III) complexes 1-6 containing two cyclometalating 2-(2,4-substitued phenyl)quinoxaline ligands and one chromophoric ancillary ligand were synthesized: (pqx)$_2Ir$(mprz) (1), (dmpqx)$_2Ir$(mprz) (2), (dfpqx)$_2Ir$(mprz) (3), (pqx)$_2Ir$(prz) (4), (dmpqx)$_2Ir$(prz) (5), (dfpqx)$_2Ir$(prz) (6), where pqx = 2-phenylquinoxaline, dfpqx = 2-(2,4-diflourophenyl)quinoxaline, dmpqx = 2-(2,4-dimethoxyphenyl)quinoxaline, prz = 2-pyrazinecarboxylate and mprz = 5-methyl-2-pyrazinecarboxylate. The absorption, emission, electrochemical and thermal properties of the complexes were evaluated for potential applications to organic light-emitting diodes (OLEDs). The structure of complex 2 was also determined by single-crystal X-ray diffraction analysis. Complex 2 exhibited distorted octahedral geometry around the iridium metal ion, for which 2-(2,4-dimethoxyphenyl)quinoxaline N atoms and C atoms of orthometalated phenyl groups are located at the mutual trans and cis-positions, respectively. The emission spectra of the complexes are governed largely by the nature of the cyclometalating ligand, and the phosphorescent peak wavelengths can be tuned from 588 to 630 nm with high quantum efficiencies of 0.64 to 0.86. Cyclic voltammetry revealed irreversible metal-centered oxidation with potentials in the range of 1.16 to 1.89 V as well as two quasi-reversible reduction waves with potentials ranging from -0.94 to -1.54 V due to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C^N ligands.
Sengottuvelan, Nallathambi,Seo, Hoe-Joo,Kang, Sung-Kwon,Kim, Young-Inn Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.8
Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo[b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: [$(pqx)_2$Ir(biim)]Cl (1), [$(dmpqx)_2$Ir(biim)]Cl (2), [$(dfpqx)_2$Ir(biim)]Cl (3), [$(btp)_2$Ir(biim)]Cl (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 - 0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from -1.15 to -1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at -1.80 V.
Nallathambi Sengottuvelan,윤성재,김대영,황인혜,강성권,김영인 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.1
A series of highly efficient red phosphorescent heteroleptic iridium(III) complexes 1-6 containing two cyclometalating 2-(2,4-substitued phenyl)quinoxaline ligands and one chromophoric ancillary ligand were synthesized: (pqx)2Ir(mprz) (1), (dmpqx)2Ir(mprz) (2), (dfpqx)2Ir(mprz) (3), (pqx)2Ir(prz) (4), (dmpqx)2Ir(prz) (5), (dfpqx)2Ir(prz) (6), where pqx = 2-phenylquinoxaline, dfpqx = 2-(2,4-diflourophenyl)quinoxaline, dmpqx = 2-(2,4-dimethoxyphenyl)quinoxaline, prz = 2-pyrazinecarboxylate and mprz = 5-methyl-2-pyrazinecarboxylate. The absorption, emission, electrochemical and thermal properties of the complexes were evaluated for potential applications to organic light-emitting diodes (OLEDs). The structure of complex 2 was also determined by single-crystal X-ray diffraction analysis. Complex 2 exhibited distorted octahedral geometry around the iridium metal ion, for which 2-(2,4-dimethoxyphenyl)quinoxaline N atoms and C atoms of orthometalated phenyl groups are located at the mutual trans and cis-positions, respectively. The emission spectra of the complexes are governed largely by the nature of the cyclometalating ligand, and the phosphorescent peak wavelengths can be tuned from 588 to 630 nm with high quantum efficiencies of 0.64 to 0.86. Cyclic voltammetry revealed irreversible metal-centered oxidation with potentials in the range of 1.16 to 1.89 V as well as two quasi-reversible reduction waves with potentials ranging from −0.94 to −1.54 V due to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C^N ligands.
Nallathambi Sengottuvelan,Hoe-Joo Seo,강성권,김영인 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.8
Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo[b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: [(pqx)2Ir(biim)]Cl (1), [(dmpqx)2Ir(biim)]Cl (2), [(dfpqx)2Ir(biim)]Cl (3),[(btp)2Ir(biim)]Cl (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 - 0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from ‒1.15 to ‒1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at ‒1.80 V.
Jayamani, A.,Sengottuvelan, N.,Kang, S.K.,Kim, Y.I. Pergamon Press 2015 Polyhedron Vol.98 No.-
The copper(II) complexes [Cu(bpy)<SUB>2</SUB>(ClO<SUB>4</SUB>)](ClO<SUB>4</SUB>) (1), [Cu(bpy)<SUB>2</SUB>(Cl)](ClO<SUB>4</SUB>) (2), [Cu(bpy)<SUB>2</SUB>(CH<SUB>3</SUB>COO)](ClO<SUB>4</SUB>) (3), [Cu<SUB>2</SUB>(bpy)<SUB>2</SUB>(μ-OH)<SUB>2</SUB>(μ-ClO<SUB>4</SUB>)<SUB>2</SUB>] (4) and [Cu<SUB>2</SUB>(bpy)<SUB>2</SUB>(μ-OH)(μ-H<SUB>2</SUB>O)(μ-CH<SUB>3</SUB>COO)](ClO<SUB>4</SUB>)<SUB>2</SUB> (5) (where bpy=2,2'-bipyridine) have been synthesized and characterized by single crystal analysis, elemental analysis and spectroscopic methods. Complexes 2 and 4 crystallize in the monoclinic P2<SUB>1</SUB>/n and C2/m space groups respectively, and the other complexes crystallize in the triclinic P1@? space group. The molecular Hirshfeld surfaces and fingerprint plots of the complexes were investigated. Complexes 1-3 exhibit one quasi-reversible and complexes 4 and 5 exhibit two quasi-reversible redox cyclic voltammetric responses near the cathodic region in DMF. Binding studies of the complexes with BSA and ctDNA showed good binding affinity. Cleavage of pBR322 DNA by the complexes shows efficient oxidative cleavage in the presence of MPA through the formation of singlet oxygen. The complexes were also screened for their antimicrobial activities, which indicated that the complexes exhibit a zone of inhibition like that of standard drugs.
김영인,Nallathambi Sengottuvelan,Hong Woo Lee,Hoe-Joo Seo,Jae Soo Choi,강성권 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.9
The reaction of copper(II) chloride with phenyl-N-[(pyridine-2-yl)methylene]methaneamide (ppmma) leads to a new μ -chloro bridged dimeric [Cu(ppmma)Cl2]2 complex, whereas a reaction of copper(II) bromide with ppmma affords a monomeric Cu(ppmma)Br2 complex. Both complexes have been characterized by X-ray crystallography and electronic absorption spectroscopy. The crystal structural analysis of [Cu(ppmma)Cl2]2 shows that the two Cu(II) atoms are bridged by two chloride ligands, forming a dimeric copper(II) complex and the copper ion has a distorted square-pyramidal geometry (τ = 0.2). The dimer units are held through a strong intermolecular π -π interactions between the nearest benzyl rings. On the other hand, Cu(ppmma)Br2 displayed a distorted square planar geometry with two types of strong intermolecular π-π interaction. EPR spectrum of [Cu(ppmma)Cl2]2 in frozen glass at 77 K revealed an equilibrium between the mononuclear and binuclear species. The magnetic susceptibilities data of [Cu(ppmma)Cl2]2 and Cu(ppmma)Br2 follow the Curie-Weiss law. No significant intermolecular magnetic interactions were examined in both complexes, and magnetic exchange interactions are discussed on the basis of the structural features.
Jayamani, A.,Sengottuvelan, N.,Kang, S.K.,Kim, Y.I. Elsevier 2014 INORGANIC CHEMISTRY COMMUNICATIONS Vol.48 No.-
The mononuclear nickel(II) complexes (1-3) of ligands bappz [1,4-bis(3-aminomethyl)piperazine] and its Schiff bases L<SUP>1</SUP> with 5-methyl salicylaldehyde; and L<SUP>2</SUP> with 5-bromosalicylaldehyde have been synthesized and characterized. The single crystal X-ray study showed that the complex 1 crystallized in the orthorhombic Pbca space group with distorted square planar geometry. The ligands and their nickel(II) complexes presented good binding propensity to bovine serum albumin protein (BSA). The strong binding interaction of the prepared complexes with calf thymus DNA (CT-DNA) was confirmed by absorption, fluorescence, circular dichroism spectral analysis and molecular docking studies in the order as follows: 3>2>1. The Schiff bases and their Ni(II) complexes were also screened for antimicrobial activity. All the complexes exhibited higher antimicrobial activity than free ligands.