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( Sunesh C D ),최영선 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.0
Light-emitting electrochemical cells (LECs) is an emerging concept for lighting; it involves an organic semiconductor material sandwiched between two metal electrodes. The use of cyclometalated Ir(III) complexes in lighting devices offers remarkably improved device performance compared to the use of other metal complexes. We report highly luminescent yellow and orange light-emitting electrochemical cells using cationic iridium complexes, i.e., [Ir(ppy)2(mpbi)]PF6 (Complex 1) and [Ir(bpbt)2(mpbi)]PF6 (Complex 2), which contain 2-phenylpyridine (ppy) and 2-(4-bromophenyl)benzothiazole (bpbt) as the cyclometalating ligands. The emissions of Complex 1 and Complex 2 are yellow and yellowish-green in acetonitrile solution. LECs incorporating Complexes 1 and 2 emit yellow (553 nm) and orange (600 nm) electroluminescence. Upon the meticulous selection of organic ligands, a significant increase in luminescence was achieved for Complex 1 (3636 cd/㎡) over that of Complex 2 (2315 cd/㎡).
Sunesh, Chozhidakath Damodharan,Mathai, George,Choe, Youngson American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.20
<P>A series of cationic iridium complexes (<B>1</B>–<B>6</B>) were synthesized using alkylated imidazole-based ancillary ligands, and the photophysical and electrochemical properties of these complexes were subsequently evaluated. Light-emitting electrochemical cells (LECs) were fabricated from these complexes, and the effects of the alkyl chain length on the electroluminescent properties of the devices were investigated. The LECs based on these complexes resulted in yellow emission (complexes <B>1</B>, <B>3</B>, and <B>5</B>) and green emission (complexes <B>2</B>, <B>4</B>, and <B>6</B>) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.49, 0.50) and (0.33, 0.59), respectively. Our results indicate that the luminance and efficiency of the LECs can consistently be enhanced by increasing the alkyl chain length of the iridium complexes as a result of suppressed intermolecular interaction and self-quenching. Subsequently, a high luminance of 7309 cd m<SUP>–2</SUP> and current efficiency of 3.85 cd A<SUP>–1</SUP> were achieved for the LECs based on complex <B>5</B>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-20/am5058426/production/images/medium/am-2014-058426_0009.gif'></P>
Sunesh, C.D.,Mathai, G.,Cho, Y.R.,Choe, Y. Pergamon Press 2013 Polyhedron Vol.57 No.-
Green and yellow light emitting phosphorescent iridium complexes with 5-methyl-1,10-phenanthroline as an ancillary ligand were synthesized and characterized for the fabrication of light-emitting electrochemical cells (LECs). The photophysical and electrochemical properties of the resulting complexes, [Ir(dfppy)<SUB>2</SUB>(Me-phen)]PF<SUB>6</SUB> (1) and [Ir(ppz)<SUB>2</SUB>(Me-phen)]PF<SUB>6</SUB> (2) (where dfppy=2-(2,4-difluorophenyl)pyridine; ppz=1-phenylpyrazole, Me-phen=5-methyl-1,10-phenanthroline) were investigated by means of UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry. Density functional theory (DFT) calculations were performed to gain insight into the photophysical and electrochemical behaviors and to determine the electronic energy levels for the complexes. LECs were fabricated based on these complexes and their electroluminescent properties were investigated, which resulted in a maximum luminance of 2430 and 1549cdm<SUP>-2</SUP> for complexes 1 and 2 respectively. LECs incorporating these heteroleptic complexes effectively tuned the emission color through the meticulous selection of the cyclometallated ligands and they displayed highly luminescent green and yellow electroluminescence with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.25, 0.58) and (0.42, 0.54) for complexes 1 and 2 respectively.
( Sunesh C D ),최영선 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1
We report the synthesis and characterization of the cationic iridium complexes [Ir(ppy)2(mpoxd)]PF6 (1), [Ir(dfppy)2(mpoxd)]PF6 (2), [Ir(piq)2 (mpoxd)]PF6 (3), and [Ir(pq)2(mpoxd)]PF6 (4). UV-visible absorption spectra, photoluminescence (PL) emission spectra, and cyclic voltammetric measurements were obtained to explore the photophysical and electrochemical properties. The significant blue shift in the emission spectrum of 2 is due to the presence of electron-withdrawing fluorine atoms on Hdfppy, which stabilizes the highest occupied molecular orbital (HOMO) to a greater extent than in the other complexes. The electrochemical and photophysical properties of the complexes were also calculated using density functional theory. The results indicate that the optical properties of the complexes can be effectively tuned by selective design of the cyclometalating and ancillary ligands.
Sunesh, C.D.,Chitumalla, R.K.,Subeesh, M.S.,Shanmugasundaram, K.,Jang, J.,Choe, Y. Elsevier S.A 2016 Journal of Electroanalytical Chemistry Vol.780 No.-
<P>We report the synthesis and characterization of the cationic iridium complexes [Ir(ppy)(2)(mPoxd)]PF6 (1), [Ir(dfppy)(2)(mpoxd)]PF6 (2), [Ir(piq)(2)(mpoxd)]PF6 (3), and [Ir(pq)(2)(mpoxd)]PF6 (4) bearing 2-phenylpyridine (Hppy), 2-(2,4-difluorophenyl)pyridine (Hdfppy), 1-phenylisoquinoline (Hpiq), and 2-phenylquinoline (Hpq) as cyclometalating ligands and 5-methyl-3-(2-pyridyl)-1,2,4-oxadiazole (mpoxd) as an ancillary ligand. UV-visible absorption spectra, photoluminescence (PL) emission spectra, and cyclic voltammetric measurements were obtained to explore the photophysical and electrochemical properties of 1-4. Depending on the nature of the cyclometalating ligands, the complexes emit yellow-orange to blue light in acetonitrile solution at room temperature. The significant blue shift in the emission spectrum of 2 is due to the presence of electron-withdrawing fluorine atoms on Hdfppy, which stabilizes the highest occupied molecular orbital (HOMO) to a greater extent than in the other complexes. The electrochemical and photophysical properties of the complexes were also calculated using density functional theory (DFT) and time-dependent DFT simulations. The results indicate that the optical properties of the complexes can be effectively tuned by selective design of the cyclometalating and ancillary ligands. (C) 2016 Elsevier B.V. All rights reserved.</P>