Note Synthesis, crystal structure, and conjugation properties of phenanthroline copper phosphine complexes Hyungsock Suh a,⇑ , Dominick J. Casadonte Jr. b , Louisa Hope-Weeks b , Han-Je Kim c , Beomsik Kim a , Taesun Chang a,⇑ a Green Chemistry Research Division, KRICT (Korea Research Institute of Chemical Technology), Yuseong, Daejeon 305-600, Republic of Korea b Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA c Department of Science Education, Kongju National University of Education, Bongwhang Dong, Gongju 314-711, Republic of Korea article info Article history: Received 27 June 2012 Received in revised form 6 August 2012 Accepted 11 September 2012 Available online 8 October 2012 Keywords: Phenanthroline Mixed ligand diimine complex Copper complex MLCT Luminescence abstract Facial synthetic method of 4,7-position conjugation extended phenanthrolines and X-ray structure of copper phosphine phenanthroline complexe were reported. The crystal structures showed p-stacking and hydrogen bonding, and a small torsional angle between phen and phenylacetylene. These complexes exhibited strong conjugation dependant MLCT luminescence. The electronic and fluorescence spectra dis- played a gradual red shift of the MLCT band as the conjugation increased. The presence of the phenyl groups reduced the energy of the p / state in the d–p / MLCT transition, allowing for the red shift. The elec- tron-donating tri-isopropylsilyl (TIPS) groups on the ethynyl moiety increased the energy of the MLCT charge vector, allowing for the blue shift at the luminescence. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The mixed-ligand metal complexes with diimines were of cur- rent interest for a wide variety of potential chemical and material applications, including electroluminescence for organic light emit- ting diode (OLED) [1], water splitting catalyst [2], luminescence quenching material [3], strong solid luminescence material [4], functional metal complexes [5], catalyst for organic synthesis [6], magnetic materials [7], electron transfer regent [8], and light in- duced hydrogen production [9]. Among these complexes, copper-based complexes are draw attention due to the low cost advantage [4]. However the emission signals from charge-transfer (CT) excited states of copper(I) com- plexes are typically weak and short-lived due to the lowest energy CT state of a d 10 system involves excitation from a metal–ligand d orbital [3]. The mixed-ligand copper systems including phosphine, however, looks promising because they exhibit strong lumines- cence with long lifetimes in the solid or frozen solution state [4]. This stimulated us to prepare phen ligands with unique substitu- tion patterns. The literatures revealed mostly the 2,9-position substituted phen, but the 4 or 7 position substituted phen were scarcely reported. Previously, one group made 4,4 0 -diethynylbipyridine, but the analogous substituted phen using the same reaction conditions could not give any desired products [10]. Another group success- fully made 4,7-diphenylethynyl-3,8-dihexylphen [11]. The hexyl groups were added to the phen to enhance the solubility, but this method could not make the simple 4,7-diacetylide phen. Very recently, one group synthesized 4,7-diethynyl phen using 4,7- dicarbaldehydehyde phen [12]. But this precursor 4,7-dicarbalde- hydehyde phen is too expensive to become a largely applicable materials. We devised the facial synthetic method of conjugated 4.7 posi- tion for phen ligands by simple modified Sonogashira reaction, and we prepared copper phosphine phenanthroline complexes to study the conjugation varible luminescnece properties followed by struc- tural confirmation with exact X-ray crystallography. 2. Experimental and results Trial with 10 mol% of copper iodide co-catalyst and check the Pd coupling reaction resulted in less than 30% yield. We found that the reaction yield dramatically enhanced when we used a copper com- plexed phen as a reactant. We envisaged that the copper (I) iodide was first chelated to the nitrogen atoms on the phen, resulting in a bis Cu(I) structure with changing the color immediately dark red. The synthetic procedure was shown in Scheme 1. The chemicals 4,7-dichloro phen [13], triisopropylsilyl acetylene, palladium 0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2012.09.028 ⇑ Corresponding author. Fax: +82 42 860 7042. E-mail addresses: hyungsuh@krict.re.kr (H. Suh), bskim@krict.re.kr (B. Kim), tschang@krict.re.kr (T. Chang). Inorganica Chimica Acta 394 (2013) 710–714 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica