Synthesis and electronic properties of meso-furyl boron dipyrromethenes

Four meso-furyl boron-dipyrromethenes (BODIPYs) were synthesized and characterized. The X-ray structures solved for three meso-furyl BODIPYs indicated the presence of an intramolecular hydrogen bond between meso-furyl ‘O’ and ‘H’ of boron-dipyrromethene core resulting in decrease of dihedral angle between the meso-furyl group and boron-dipyrromethene core leading to better electronic interaction. However, the hydrogen bonding is absent in solution as confirmed by NMR studies in different solvents. The presence of meso-furyl group alters the electronic properties of BODIPY which reflected in the downfield shifts in 1H NMR, bathochromic shifts in absorption and emission bands compared to the meso-tolyl BODIPY. The electrochemical studies indicated that the meso-furyl BODIPYs are easier to reduce compared to meso-tolyl BODIPYs. DFT studies showed that the HOMO-LUMO energy gap is decreased in meso-furyl BODIPYs compared to meso-tolyl BODIPY which is in agreement with the experimental observations.