Synthesis, spectral and crystal structures of gem-dibromovinyl boron dipyrrins

Abstract

A series of BODIPYs (boron-dipyrromethene dyes; 4,4-difluoro-5-aryl-4-bora-3a,4a-diaza-s-indacene) derivatives, bearing an aldehyde group at different pyrrole positions, were transformed into gem-dibromovinyl analogs using the Corey-Fuchs or Lautens olefination method. The gem-dibromovinyl moieties (one or two) are symmetric/asymmetric and attached at α- or β-positions of the pyrrole ring, directly or through the extension of a β-position substituted phenyl spacer ring. The molecular structures of the resultant dyes were assigned using MS, 1H, 13C, 19F NMR, X-ray diffraction and for some compounds 2D HSQC and 11B NMR. The absorption, fluorescence and solvatochromism properties were investigated in different solvents. The highest absorption and emission maxima were obtained for compounds having two gem-dibromovinyl groups attached directly at the α-positions. The best correlation (R-coefficient) of absorption between the solvents and spectral properties of the BODIPYs was obtained using the refractive index of the solvent. The R-coefficient of emission was obtained only for compounds having gem-dibromo vinyl moieties at α-positions. Their solid states clearly reveal distinct patterns of gem-dibromovinyl orientation, torsion angles of the 5-phenyl ring and the indacene plane. Hirshfeld surface analyses were used to visualize various intermolecular interactions.