Synthesis and studies of meso-3-pyrrolyl BODIPYnyl porphyrins†

Abstract

New meso-substituted porphyrins containing one to four 3-pyrrolyl BODIPY units at the meso-positions named meso-3-pyrrolyl BODIPYnyl porphyrins were synthesized in 15–20% yields by condensing meso-4-formyl phenyl-3-pyrrolyl BODIPY, benzaldehyde, and pyrrole in different molar ratios under acid catalyzed conditions. The identities of meso-3-pyrrolyl BODIPYnyl porphyrins were confirmed by HR-MS and detailed 1D & 2D NMR spectroscopy. meso-3-Pyrrolyl BODIPYnyl porphyrins showed a strong Soret band at 427 nm and weak Q-bands in the 500–650 nm region corresponding to the porphyrin unit whereas the 3-pyrrolyl BODIPY unit absorbs strongly in the 500–600 nm region. Thus, the absorption bands of the meso-3-pyrrolyl BODIPYnyl porphyrins in the Q-band region were significantly enhanced as the number of 3-pyrrolyl BODIPY units increases from one to four at meso-positions. The meso-3-pyrrolyl BODIPYnyl porphyrins were stable under both acidic and basic conditions. The steady-state and time-resolved fluorescence studies indicated a possibility of singlet–singlet energy transfer from 3-pyrrolyl BODIPY units to the porphyrin unit and a maximum energy transfer efficiency of 81% was observed for the meso-tetra 3-pyrrolyl BODIPYnyl porphyrin. DFT and TD-DFT studies were in agreement with the experimental observations.