Studies on Cyanine Dyes (XXXIV)

Syntheses and Absorption Spectra of Cyanine Dyes Having Pyrazineor Quinoxaline Nucleus

Abstract

Eight unsymmetrical carbocyanine dyes, eight hexamethine-hemicyanine dyes, containing pyrazine (P) nucleus, and five unsymmetrical carbocyanine dyes, containing quinoxaline (Q) nucleus were snythesized. And their absorption max. were determined. As for the relationship between basicity of P nucleus or Q nucleus and the absorption max. of their dyes, following results were obtained.
(1) As basicity of the amine in the hemicyanines increase, absorption max. of the dyes containing P nucleus shifts to the longer wavelength.
(2) Concerning the relations above mentioned, (P) effects largier influence to their ab. max. than benloxazole or benzothiazole nucleus, the latter had been reported previously.
(3) Basicity of P nucleus is nearly about pKa 7.7.
(4) Basicity of Q nucleus corresponds to benzoxazole nucleus.
(5) Absorption spectra of unsymmetrical carbocyanine dyes containing Q nucleus show a shoulder at long wavelength side.