228 © Color. Technol., 121 (2005) Web ref: 20050409 Coloration Technology Society of Dyers and Colourists Synthesis and characterisation of monomethine cyanine dyes based on N-bridgehead heterocycles R M Abd El-Aal,* A I M Koraiem and N M Salah El-Deen Chemistry Department, Aswan Faculty of Science, South Valley University, Aswan, Egypt Email: abdelal2001@yahoo.com Received: 8 March 2005; Accepted: 31 May 2005 In this paper, the synthesis and spectral properties of novel asymmetrical and symmetrical monomethine cyanine dyes are described. Reaction of phenylpyrazolones and oxazolones with acetyl thiourea and/or thiosemicarbazide afforded acetyl intermediate compounds which were then reacted with metal divalent chlorides, followed by reaction with N-methyl hetetrocyclic quaternary salts, to give asymmetrical monomethine cyanine dyes. Reaction of the 5-amino derivative of the intermediate compounds with acetaldehyde followed by reaction with N-methyl hetetrocyclic quaternary salts produced the symmetrical monomethine cyanine dyes. These new compounds were characterised with elemental analyses, visible absorption and infrared spectrometry, and 1 H/ 13 C NMR and mass spectroscopy. The correlation between the colour and structure of these dyes was also investigated. Introduction Methine cyanine dyes have attracted much attention over the years because of their applications in various fields, such as near-infrared laser dyes [1] and in optical data recording [2]. These dyes interact with nucleic acids and photo-damage DNA [3]. They have also been used in dye- sensitised photopolymers [4], CD-R [5] and dye-sensitised porous semi-conductor electrodes [6]. The majority of methine cyanine dyes reported for use in optical recording materials belong to the class of symmetrical methine cyanine; whereas asymmetrical methine cyanines have superior optical properties [7,8]. Addition of transient metal chelate compounds as quenchers to cyanine dyes increases their photostability and inhibits their decolorisation by light [9], as well as increasing their resistance to heat and moisture [10]. In this paper, the synthesis and spectral properties of novel asymmetrical and symmetrical monomethine cyanine dyes, which might be used in different optical applications, are described. Experimental Materials and methods All melting points are uncorrected. Elemental analyses were carried out at the Microanalytical Center (Cairo University). Infrared (IR) spectra were determined with a Perkin Elmer Infrared 127β spectrophotometer (Cairo University) using a KBr disc. Nuclear magnetic resonance ( 1 H NMR) spectra were recorded with a Bruker AMX-250 spectrometer. Two- dimensional 1 H and 13 C NMR (CDCl 3 , 250 MHz) spectra measured with a Bruker AMX-400 spectrometer, with tri- methylsilane as an internal standard. COSY spectra were recorded to confirm 1 H– 1 H and 1 H– 13 C connectivities based on vicinal and geminal couplings, along with HMBC spectra to measure the location and intensity of correlations in the contour plots. Mass spectra were recorded on an HpMs 6988 spectrometer (Cairo University). The electronic absorption spectra were recorded within the wavelength range (λ max 350–700 nm) with a 6405 UV/Visible recording spectrophotometer (Faculty of Science, Aswan). Solvents, chemicals and reagents were purchased from Merck unless stated otherwise and purified and dried according to standard procedures. Synthetic studies For each of the compounds synthesised in this study, satis- factory analytical data was obtained; only the data for key compounds are given in this paper (see Tables 1 and 2). 4-Benzylidenopyra-/oxa-zolones 1a–f 4-Arylideno-3-methyl-1-phenylpyrazolones (1a– c,f ), and the 4-arylideno-2-methyloxazolone derivatives (1d,e), were synthesised according to literature procedures [11–13]. O R 1a 1b 1c 1f R = H R = OCH 3 R = NO 2 R = OH N O H 3 C O R 1d 1e R = H R = NO 2 N N CH 3 Ph 5-Acetyl- and 5-amino-pyrazolo/oxazolo[4,5-d]pyrimidino- thiones 2a–k Cyclocondensation of compounds 1a–f with acetylthiourea and/or thiosemicarbazide in absolute ethanol (containing concentrated hydrochloric acid) afforded the corresponding pyrimidine-6-thiones 2a – k, according to literature procedures (Scheme 1) [11–13].