Syntheses, Spectroscopic Properties, and Computational Study of ( E, Z)-Ethenyl and Ethynyl-Linked BODIPYs

A series of ( E, Z)-ethenyl- and ethynyl-linked boron dipyrromethene (BODIPY) dimers were synthesized in 23-34% yields by condensation of pyrroles with the corresponding bis-benzaldehydes, followed by oxidation and boron complexation. The BODIPY dimers were characterized by ¹H, ¹³C, and ¹¹B NMR spectroscopy, high-resolution mass spectrometry, and, in the cases of 1b, 2, and 3, by X-ray crystallography. The spectroscopic properties for this series of dimers were investigated in tetrahydrofuran solutions, and very similar absorption and emission profiles were observed for all dimers. Density functional theory calculations show minimal conjugation between the two BODIPY units in the dimers, as a result of the large dihedral angle between the BODIPYs and the linker. The ( E)-ethenyl-linked dimer 1a showed the highest fluorescence quantum yield of all dimers investigated in this study.