Polybrominated BOPHY Dyes: Synthesis, Reactivity, and Properties

A series of mono- to hexabrominated BOPHY dyes have been regioselectively synthesized in 41-96% yields from bromination of parent bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (BOPHY), bromination of hydrazine-linked bispyrrole intermediate, or brominated 2-formylpyrrole precursors in moderate to excellent yields. The reactivities of these polybrominated BOPHY dyes were further studied via regioselective nucleophilic substitution or Suzuki/Stille cross-coupling reactions from which a series of 5- or 5,5'-substituted BOPHYs with amine, pyrrole, thiophene, and phenyl groups were obtained in moderate to high yields of 37-94%. The regioselectivities of both the bromination and nucleophilic substitution reaction, and these resultant BOPHY dyes, are confirmed by NMR, HRMS, and crystal structures. The spectroscopic properties of these resultant BOPHYs were studied, and most of them showed strong absorbance and bright fluorescence with maximum wavelengths centered at between the range of 430 and 660 nm. Their absorption and emission spectra were red-shifted for each bromine atom incorporated. The positions in which bromines or substituents are attached modulate the photophysical properties of the resulting BOPHY dyes.