Synthesis and photophysics of a new deep red soluble phosphorescent iridium(III) complex based on chlorine-methyl-substituted 2,4 diphenyl quinoline H.K. Dahule a , S.J. Dhoble b , J.-S. Ahn c , Ramchandra Pode c,n a Department of Physics, Shivaji Science College, Congress Nagar, Nagpur 440012, India b Department of Physics, Rashatrasant Tukadoji Maharaj Nagpur University, Nagpur 440033, India c Department of Physics, Kyung Hee University, 1-Hoegi-dong, Dongdaemun-gu, Seoul 130-701, Republic of Korea article info Article history: Received 13 December 2010 Received in revised form 28 May 2011 Accepted 10 September 2011 Available online 17 September 2011 Keywords: A. Iridium complex A. Chlorinated quinoline B. X-ray diffraction B. Thermogravimetric analysis (TGA) B. Photoluminescence C. Deep red emitter abstract A new iridium complex with a chlorine-methyl-substituted 2,4 diphenyl quinoline, (Cl-MDPQ) ligand has been synthesized. The synthesized iridium metal complex, Ir(Cl-MDPQ) 2 (acac) where Cl-MDPQ¼chlorine- methyl substituted, 2,4 diphenyl quinoline, acac ¼acetyl acetone is characterized by employing different techniques such as mass spectrometry, 1 H NMR, DTA/TGA, XRD, and FTIR. The molecular structures of Cl-MDPQ and Ir(Cl-MDPQ) 2 (acac) complexes are confirmed by the FTIR spectra. Strong singlet metal-to- ligand charge-transfer ( 1 MLCT) and triplet metal-to-ligand charge-transfer ( 3 MLCT) absorption peaks at 353 and 437 nm in tetrahydrofuran (THF) are reported in the synthesized complex, respectively. A deep red emitting Ir(Cl-MDPQ) 2 (acac) complex at 662 nm is promising for flexible organic devices. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Solution-processed organic light-emitting-diode devices (OLEDs) are acquiring the mainstream position as potential candidates for flat-panel displays and solid state lighting owing to their simple processing route and low manufacturing cost [1–3]. OLEDs fabri- cated employing the solution processes such as spin coating and inkjet printing are promising for large flexible devices. Mostly, the soluble iridium organic complexes are used in the fabrication of solution-processed red-emitting OLEDs [4–10]. Indispensable requirements for such solution process devices are good solubility and film forming property of the constituting materials. Although several Ir(III)-based phosphorescent complexes have been devel- oped, the synthesis of good soluble Ir(III) complex having high quantum yields is still an open issue. Various red emitting soluble Ir(III) phosphorescent complexes are summarized in Table 1 [7,9,11–20]. Amongst these, the Ir(piq) 3 [12] and Ir(btp) 2 (acac) [11] are well known red phosphorescent emitters (where piq and btp are 1-phenylisoquinolinato-N,C 2 0 and 2-(2 0 -benzo[b]thienyl)pyri- dinato-N,C 3 0 ligands, respectively). However, their photolumines- cence quantum yields in solution are not sufficient. In fact, it was found that the Ir(piq) 3 is insoluble in many common solvents such as p-xylene, chlorobenzene, and toluene [12]. In order to use the cost competitive solution process for the device fabrication with a high performance, the highly emissive soluble Ir(III) red phosphorescent materials are required. Furthermore, the synthesis of efficient red emitters is intrinsi- cally more difficult since their luminescence quantum yields tend to decrease as the emission wavelength increases in accordance with the energy gap law [21]. The cyclometalated iridium com- plexes used in electroluminescent (EL) devices are octahedral, with a 3 þ oxidation state, and exhibit a strong phosphorescence primarily from the triplet metal-to-ligand charge-transfer ( 3 MLCT) or a ligand-centered 3 p–p* transition [11]. To date, the deep red phosphorescent iridium complex from the quinoline ligand has not been reported. In this paper, we synthesized a chlorine-methyl substituted, 2,4 diphenyl quinoline and used as a ligand to synthesize the red iridium complex, Ir(Cl-MDPQ) 2 (acac) where Cl-MDPQ¼ chlorine- methyl substituted, 2,4 diphenyl quinoline and acac ¼ acetyl acet- one, instead of common isoquinoline. The absorption of the complex was measured in the visible region in different organic solvents such as acetic acid, formic acid, and tetrahydrofuran (THF). The complex was found to emit a deep red phosphorescence emission peaking at 662 nm. The easy synthesis process, thermal stability, good solubi- lity in common organic solvents of deep red emitting Ir(Cl-MDPQ) 2 (acac) phosphorescent complex are reported. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jpcs Journal of Physics and Chemistry of Solids 0022-3697/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2011.09.011 n Corresponding author. Tel.: þ82 10 5169 3510. E-mail address: rbpode@khu.ac.kr (R. Pode). Journal of Physics and Chemistry of Solids 72 (2011) 1524–1528