Bridged Bis-BODIPYs: synthesis, structures and properties

Abstract

A series of bis-BODIPYs 1-6 bridged via thiophene, furan, N-alkylcarbazole, triphenyl amine, para- and meta-phenylene groups have been synthesized and characterized by various spectroscopic techniques. The change in spectroscopic properties of bis-BODIPYs upon varying the size of spacer was studied. X-ray crystal structures of three bis-BODIPYs containing triphenylamine, para- and meta-phenylene bridges were solved. Intermolecular C(H)----andstacking interactions were observed in solid state structures of three bis-BODIPYs. The dihedral angles between the spacer unit and two borondipyrrin units were lower in all three compounds as compared to their corresponding monomers. This suggests increased interactions between the two boron-dipyrrin units in molecules which in turn reflected in the anodic shifts in their reduction potentials. DFT studies indicated effective electronic interactions between spacers and two boron dipyrrins units in all the bis-BODIPYs. The calculated HOMO-LUMO gap was found to be lower for bis-BODIPY having bulky carbazole spacer and higher for bis-BODIPY having smaller furan spacer. The change in spacer size clearly affected the spectroscopic properties of the bis-BODIPYs and red shifted absorption and emission maxima were observed for bis-BODIPYs with furan and thiophene spacers as compared to bis-BODIPYs with phenylene or bulky aromatic spacers.