HETEROCYCLIC HALIDE MOIETIES IN THE SYNTHESIS AND STUDY OF SOME CONJUGATED OXAZINE METHINE CYANINE DYES

New asymmetrical/symmetrical styryl cyanines (<(3a)under bar>-(d) unde r bar,<(4a)under bar>-(d) under bar), monomethine cyanine dyes (<(5a)u nder bar>-(d) under bar,<(6a)under bar>-(d) under bar) and trimethine cyanine dyes (<(11a)under bar>-(g) under bar,<(12a)under bar>-(g) unde r bar) incorporating bis pyrazolo-[2,3-b;2',3'-b'] oxazine and/or pyra zolo [2,3-b]-oxazolo [2',3'-b] oxazine were prepared. The new synthesi sed cyanines were identified by elemental and spectral analyses. The u v-visible absorption spectra of some selected dyes were investigated i n pure and mixed solvents as well as in aqueous buffer solutions. Mole cular complex formation with ethanol was verified by mixed solvent stu dies. Electronic transitions were attributed to either locally excited or predominantly charge transfer states. The spectral shifts were dis cussed in relation to molecular structure and in terms of medium effec ts. The variation of absorbance with pH was utilized for the determina tion of the pKa values for some selected compounds.