Syntheses and electronic absorption spectra of some new penta- and di-methine cyanine dyes

Abstract

The reaction of a ratio of 1 mole of 5-chloro-3-methyl-1-phenyl pyrazolo-4[2(4)]-dimethine cyanine (1a,b) or (5-chloro-4-formyl-3-methyl-1-phenylpyrazole) 2 with 2 moles of an appropriate 2(4)-heterocyclic quaternary salt afforded the novel pentamethine cyanine dyes (3a–3e). Other reactions of 2 with heterocyclic nitrogen bases, followed by condensation of the newly formed quaternary nitrogen salts (4a–4c) with methoheterocyclic iodide salts provided the corresponding unsymmetrical dimethine cyanine dyes (5a–5g). The new pentamethine and dimethine cyanine dyes were identified by elemental analyses and IR and 1H-NMR spectral data. The visible absorption spectra of some selected dyes were investigated in pure and mixed solvents as well as in universal buffer solutions. The measure of the variation of absorbance with pH was utilized for the determination of the pKa values for compounds 3b, 3d, 3e, 5e, and 5f, and these data are discussed. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 259–266, 1997.