Efficient energy transfer in phenyl-ethynyl-linked asymmetric BODIPY dimers

Abstract

Abstract Three asymmetric boron dipyrromethene (BODIPY) dimers were synthesized via coupling of a BODIPY monomer with a meso-phenyl ethynyl group substituent to the different monomers with an iodine atom at the second position of the BODIPY core. The dimers were characterized by 1H, 13C, and 11B, 19F NMR spectroscopy and high-resolution mass spectrometry. Density functional theory calculations show minimal conjugation between the two BODIPY units in the dimers due to a large dihedral angle between the BODIPYs and the linker. Absorption and fluorescence measurements of monomeric and dimeric compounds in dichloromethane indicated highly efficient singlet-singlet energy transfer between two BODIPY units (in which the meso-phenyl containing BODIPY unit act as the donor while the other BODIPY unit is the acceptor) and large Stokes shifts. In particular, the dimer with the styryl BODIPY unit absorbs light in a wide range of the spectrum (325 nm–690 nm) with emission in the near IR region. The ethynyl thiophene linked dimer showed the highest fluorescence quantum yield (76%) of all three dimers investigated in this study.