Synthesis, Structure, Spectral and Electrochemical Properties of 5,6,7,9,10,11-Hexaaryl Substituted Meso-(p-Tolyl) 3-Pyrrolyl BODIPYs

Hexabrominated meso-(p-tolyl) 3-pyrrolyl BODIPY was regioselectively synthesized by treating meso-(p-tolyl) 3-pyrrolyl BODIPY with eight equivalents of Br₂ in CH₂Cl₂ under inert atmosphere at room temperature. Five different 5,6,7,9,10,11-hexaarylated meso-(p-tolyl) 3-pyrrolyl BODIPYs were synthesized by treating 5,6,7,9,10,11-hexabromo meso-(p-tolyl) 3-pyrrolyl BODIPY with various boronic acids under Suzuki coupling conditions. The X-ray structure obtained for hexabromo and hexaarylated 3-pyrrolyl BODIPYs showed slightly distorted structures. Absorption spectral studies revealed that the absorption bands in hexabromo and hexaarylated 3-pyrrolyl BODIPYs were bathochromically shifted compared to 3-pyrrolyl BODIPY. The hexabromo 3-pyrrolyl BODIPY was less fluorescent due to presence of heavy halogens whereas the hexaarylated 3-pyrrolyl BODIPYs emits moderately in the region of 687–736 nm with quantum yields in the range of 0.18–0.30 and singlet state lifetimes in 2.99–4.50 ns range. The electrochemical studies revealed that hexabrominated 3-pyrrolyl BODIPY undergo easier reduction compared to 3-pyrrolyl BODIPY. The hexaarylated 3-pyrrolyl BODIPYs showed one reversible/quasi-reversible oxidation and one reversible reduction and their redox behaviour depends on the type of electron donating or electron withdrawing substituents present at the pyrrole carbons. DFT/TD-DFT studies were in agreement with the experimental results. Group webpage: https://ravikanthlab.wixsite.com/mysite/