Carbazole substituted boron dipyrromethenes.

meso-Substituted BODIPY with N-butylcarbazole (1) was prepared and derivatized. Dibromo BODIPY 2, alpha-formyl BODIPY 3 and beta-formyl BODIPY 4 were synthesized. All compounds were characterized by HRMS, NMR, UV-vis absorption, electrochemical and fluorescence techniques. The crystal structures of BODIPY 1 and its dibromo derivative 2 were also solved. In both the X-ray structures, the dihedral angle between the meso-carbazole group and the dipyrrin plane was decreased, suggesting the increased interaction between the two units. meso-Substitution with the N-butylcarbazole group on the BODIPY core rendered huge Stokes shifts (111-168 nm) and higher quantum yields as compared to meso-aryl BODIPY. An efficient energy transfer from the carbazole unit to the BODIPY core was observed by fluorescence spectroscopy for all the compounds 1-4. CV studies of compounds 1-4 showed anodic shifts of the reduction and oxidation potentials, suggesting that the meso-carbazole group is affecting the electronic properties of the BODIPY core and making them easier to reduce.