The synthesis of highly fluorescent heterocyclic compounds: Pyrido[2 0 ,1 0 :2,3] imidazo[4,5-b]quinoline-12-yl cyanides Mohammad Rahimizadeh * , Mehdi Pordel, Mehdi Bakavoli, Hossein Eshghi Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, Mashhad 91775-1436, Iran article info Article history: Received 27 September 2009 Received in revised form 11 January 2010 Accepted 13 January 2010 Available online 1 February 2010 Keywords: Quinolines Imidazo[1,2-a]pyridine Dye Absorption Emission Fluorescence abstract The syntheses and fluorescence properties of novel derivatives of pyrido[2 0 ,1 0 :2,3]imidazo[4,5-b]quino- line are described. The key intermediates (4-substituted)(3-hydroxyimino-2,3-dihydroimidazo[1,2-a] pyridin-2-yliden)methyl cyanides were synthesized by reacting the imidazo[1,2-a]pyridine with aryla- cetonitriles via nucleophilic substitution of hydrogen. The compounds were deep violet in colour. Acylation of hydroxyl group led to heterocyclization and gave highly fluorescent pyrido[2 0 ,1 0 :2,3]imidazo [4,5-b]quinoline. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Fluorescent heterocyclic compounds are of interest in many disciplines such as emitters for electroluminescence devices [1], molecular probes for biochemical research [2], in traditional textile and polymer fields [3], fluorescent whitening agents [4] and photo conducting materials [5]. Quinolines are well-known fluorescent compounds of high quantum yield and have attracted much attention owing to their potential high technology applications [6e9] including fluorescence probes in chemosensors [10,11]. Quinolines are, in general, comparatively easy to prepare, and numerous derivatives have been described for potential use as biologically active materials [12,13]. Several classical synthetic methods can be used to prepare quinolines, including the Skraup synthesis that involves heating aniline with glycerol and nitro- benzene in the presence of sulfuric acid [14], the Combes quinoline synthesis [15], Friedländer synthesis [16] and other methods [17e19]. Imidazo[1,2-a]pyridine derivatives are also well-known fluorescent compounds, as exemplified by imidazo[1,2-a]pyr- idinium salts, which are used to prepare styryl dyes [20] and imi- dazopyridine-7-nitrofurazan conjugates which have been utilized as fluorescent probes for the localization and function of the peripheral benzodiazepine receptor (PBR) [21]. Based on these aspects, it was decided to synthesize a heterocyclic system that contained both imidazo[1,2-a]pyridine and quinoline rings and to study their fluorescence properties. Continuing the authors’ study of the nucleophilic substitution reactions of hydrogen [22e25], it was decided to use these reactions in the synthesis of novel derivatives of (3-hydroxyimino-2,3-dihydroimidazo[1,2-a]pyridin- 2-yliden)-2-phenylacetonitrile 3aee as key intermediates. In this paper, a new method for the synthesis of several novel, highly fluorescent derivatives of pyrido[2 0 ,1 0 :2,3]imidazo[4,5-b]quinolines 4aee, is described. 2. Experimental 2.1. Equipment and materials Melting points were recorded on an Electrothermal type 9100 melting point apparatus. The IR spectra were obtained on a 4300 Shimadzu spectrometer and only noteworthy absorptions are listed. The 1 H NMR (500 MHz) and the 13 C NMR (125 MHz) spectra were recorded on a Bruker Avance DRX-500 Fourier transformer spectrometer. Chemical shifts are reported in ppm downfield from TMS as internal standard; coupling constance J are given in Hertz. The mass spectra were scanned on a Varian Mat CH-7 at 70 eV. Elemental analyses were performed on a Thermo Finnigan Flash EA microanalyzer. Absorption spectra were recorded on an Agilent * Corresponding author. Tel.: þ98 511 879 7022; fax: þ98 511 879 6416. E-mail address: rahimizh@yahoo.com (M. Rahimizadeh). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2010.01.013 Dyes and Pigments 86 (2010) 266e270