A facile method for the synthesis of 1- and 2-pyridylazulenes, and of 1,3-dipyridylazulenes, is described.Color and spectral changes of these pyridylazulenes upon the addition of either acid or metal ions wereinvestigated in detail. The color changed from blue to red upon the addition of trifluoroacetic acid or softmetal ions, depending on the substitution patterns of the pyridyl group on the azulene skeleton. Thestructures of the protonated or coordinated products were examined on the basis of the spectral data. Itwas found that the protonation or coordination of metal ions occurred on the nitrogen atom of the pyridinering, but not on the carbon atom of azulene ring. The transition intervals of several pyridylazulenes foruse as pH indicators were also determined.
