Phosphorescence of BODIPY dyes

The phosphorescence of BODIPY dyes was observed directly in glassy solvent matrix at 78 K. The phosphorescence occurred when Br substituents are present on the BODIPY core and the solvent temperature is lower than the freezing point. The phosphorescence quantum yield (Φp) and lifetime (τp) were measured. The substitution effect of Br atoms on the phosphorescence properties of 8-phenyl-BODIPY dyes is also studied. Upon the increase in the number of Br atoms on the BODIPY core, the phosphorescence emission maximum is varied from 720 to 780 nm, the corresponding excited triplet state energy changes from 1.71 to 1.62 eV, the lifetime τp is shortened from 5.8 to 3.7 ms, while the quantum yield Φp is decreased from 3.0 × 10−3 to 1.4 × 10−3. The mechanism for the effect of Br substitution on the phosphorescence properties is revealed by calculating the rate constants of related photophysical processes. The Br substitution at position 1 or 7 showed a dramatic difference from that at positions 2, 6, 3, and 5. The steric hindrance to the rotation of the phenyl leads to the deformation of BODIPY π-core such that the phosphorescence properties change toward a different direction.