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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.
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.
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.
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.
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.
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.
Lee, Hong-Woo,Sengottuvelan, Nallathambi,Seo, Hoe-Joo,Choi, Jae-Soo,Kang, Sung-Kwon,Kim, Young-Inn Korean Chemical Society 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 $\mu$ -chloro bridged dimeric [Cu(ppmma)$Cl_2$]$_2$ complex, whereas a reaction of copper(II) bromide with ppmma affords a monomeric Cu(ppmma)$Br_2$ complex. Both complexes have been characterized by X-ray crystallography and electronic absorption spectroscopy. The crystal structural analysis of [Cu(ppmma)$Cl_2$]$_2$ 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 ($\tau$ = 0.2). The dimer units are held through a strong intermolecular $\pi-\pi$ 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)$Cl_2$]$_2$ in frozen glas s at 77 K revealed an equilibrium between the mononuclear and binuclear species. The magnetic susceptibilities data of [Cu(ppmma)$Cl_2$]$_2$ and Cu(ppmma)$Br_2$ 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.
강성권,Hong Woo Lee,Nallathambi Sengottuvelan,김영인 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.1
Two novel copper(II) complexes, [Cu(dmamhp)(H2O)2(SO4)]n (1) and [Cu(dmamhp)(NO3)2(H2O)]·H2O (2)[dmamhp = 2-dimethylaminomethyl-3-hydroxypyridine] have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 displays a double one-dimensional chains structure,in which each chain is constituted with the distorted octahedral copper(II) complex bridged through bidentate sulfate ligands resulting in a coordination polymer. The bifurcated hydrogen bonds and π-π interactions play important roles in the formation of the double chains structure. On the other hand, compound 2 adopts a distorted square pyramidal geometry around copper(II) ion and exists as a discrete monomer. There are intermolecular bifurcated hydrogen bonds and π-π stacking interactions between the monomeric units. The magnetic properties revealed that the paramagnetic behaviors are dominantly manifested and there are no intermolecular magnetic interactions in both compound 1 and 2.