Palladium catalyzed homocoupling reactions of gem-dibromo BODIPYs: Formation of dimer and trimer products

We report on the synthesis and spectral properties of BODIPY 1,3-diyne dimers and 1,1-diynyl-1-alkene trimers, prepared via the Pd-catalyzed homocoupling reaction of a series of gem-dibromovinyl BODIPY (1,1-dibromo-1-alkene 4,4-difluoro-5-aryl-4-bora-3a,4a-diaza-s-indacene) dyes. The dimer and trimer moieties are connected through the ethynyl bond, attached at p-meso-phenyl or β-positions of the pyrrole ring, directly or through the phenyl spacer ring at the β-position. The assigned molecular structures of the products were confirmed using MS, ¹H, ¹³C, ⁹F NMR and ¹¹B NMR spectroscopic techniques. The absorption, fluorescence and solvatochromic properties were investigated in different solvents. The absorption maxima of unsubstituted pyrrole derivatives are bathochromic shifted as compared to the tetramethyl pyrrole substituted analogs. The highest absorption maxima were obtained when unsubstituted pyrrole 1,1-diynyl-1-alkene trimers featured a phenyl ring at the β-position. Dimers do fluoresce while trimers are void of fluorescence properties.