Synthesis of 5-alkoxymethyl- and 5-aminomethyl-substituted 8-hydroxyquinoline derivatives and their luminescent Al(III) complexes for OLED applications Amaresh Mishra, * Pabitra K. Nayak and N. Periasamy Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India Received 6 May 2004; revised 16 June 2004; accepted 22 June 2004 Abstract—Several 5-alkoxymethyl- and 5-aminomethyl-substituted 8-hydroxyquinolines were synthesised. Their coordination com- plexes with Al(III) were also synthesised. These complexes are soluble and stable in common organic solvents and show green lumi- nescence with high quantum yields. Ó 2004 Elsevier Ltd. All rights reserved. The synthesis and implementation of new charge-trans- porting and emissive materials in organic light emitting devices (OLEDs) has afforded much fundamental infor- mation and has resulted in greatly enhanced quantum efficiency, brightness and stability. Tris-(8-hydroxyquino- line) aluminium (AlQ 3 ), an efficient green electrolumi- nescent material, was first used as an electron transporter and photon emitter in organic light emitting devices by Tang and VanSlyke. 1 Since then it has been a workhorse material for use in OLED applications. 2 AlQ 3 is a spherically shaped molecule with distorted octahedral geometry, where the 8-hydroxyquinoline lig- ands surround the Al(III) ion. The molecule has low photoluminescence (PL) quenching in the solid state, good electron mobility and good stability against recrys- tallisation as an amorphous thin film. Many researchers have attempted the discovery of new and improved or- ganic materials based on 8-hydroxyquinoline for OL- EDs. 3 The use of AlQ 3 with various dyes as dopants shows substantial promise in the development of new light sources of different colour. Though AlQ 3 is used as a good electron transporter in single and bi-layer de- vices, it has to be vapour deposited for thin film forma- tion. Our aim here was to synthesise materials, which could be easily spin-castable from organic solution. This could be a gentler process and might also retain the molecular features of the material. Keeping this in mind, we have synthesised a family of 8- hydroxyquinoline derivatives by substituting at the 5- position. These molecules were designed to have high solubility in many organic solvents and to serve the pur- pose of spin-coating. Their photoluminescence proper- ties in solution have been investigated. The ligands were designed in order to achieve better sol- ubility without affecting the beneficial spectroscopic and luminescence properties. The solubility was enhanced by attaching a functional group to the ligand. The ligands reported here have aromatic groups attached at the 5- position through an –OCH 2 – or –NCH 2 – as the link. The –CH 2 – group ensures minimal effects on the aro- matic properties of the ligand, irrespective of the group substituted. 5-Chloromethyl-8-hydroxyquinoline hydrochloride 1 was synthesised as reported earlier by the reaction of 8-hydroxyquinoline with formaldehyde and concen- trated HCl. 4 Condensation of 1 with an excess of appro- priate alcohols or amines in the presence of NaHCO 3 gave the corresponding 5-substituted products (Scheme 1). These ligands were purified by crystallisation from appropriate solvents to give 50–60% yields. The com- pounds were characterised by 1 H NMR, 13 C NMR, ESI-MS and elemental analysis. 5 The mass spectra of 2, and 3 exhibited intense peaks at 301.8 and 302.07 0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2004.06.089 Keywords: 8-Hydroxyquinoline derivatives; Al(III) complexes; Absorp- tion and photoluminescence spectra. * Corresponding author. Tel.: +91-22-2280-4545; fax: +91-22-2280- 4610; e-mail: amishra@tifr.res.in Tetrahedron Letters 45 (2004) 6265–6268 Tetrahedron Letters