Hexaethylsubporphyrins: β-alkyl analogues in the subporphyrin family

Abstract

Two new subporphyrins were synthesized for the first time from a β-substituted pyrrole i.e. 3,4-diethylpyrrole via pyridine-tri-N-(3,4-diethylpyrrolyl)borane as building blocks. These β-hexaethylsubporphyrins are true contracted congeners of β-octaethylporphyrin (OEP). While the meso-triphenyl derivative of hexaethylsubporphyrin could be synthesized by following the reported method, the meso-free analogue could only be synthesized by condensation with trioxane, in the presence of catalytic methanesulfonic acid. These contracted macrocycles display interesting absorption, and emission behaviour including substituent dependent S₂ fluorescence owing to the presence of flexible electron donating ethyl groups at their β-positions. The optical response and ultrafast S₂ state dynamics of these systems suggest that it may be possible to tune the properties of the subporphyrin to develop efficient systems for solar energy capture and conversion processes.