Boradipyrromethenecyanines derived from conformationally restricted nuclei

A series of meso-polymethine-substituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes were synthesized based on the reaction of meso-methyl borondipyrromethene with a number of hemicyanine derivatives. The dyes obtained exhibited a weak short-wavelength absorption, a strong long-wavelength absorption and weak fluorescence. Upon protonation, the long-wavelength band disappeared while the intensity of the short-wavelength band increased markedly. The properties of the dyes were closely related to those merocyanine dyes rather than borondipyrromethenes.