Synthesis of nonaromatic [16]thiatriphyrin(2.2.1)s

Abstract

[16]Thiatriphyrin(2.2.1)s containing one thiophene and two pyrroles connected via five meso-carbons were synthesized by condensing a new precursor, meso-fused thiatripyrrane, with an appropriate aryl aldehyde in CH₂Cl₂ under acid-catalyzed inert conditions followed by open air oxidation with DDQ. These are the first examples in a new series of stable triphyrin(2.2.1)s and both experimental and theoretical studies indicated the nonaromatic nature of the macrocycles. The macrocycles showed strong absorptions in the UV-visible region and exhibited easier oxidations and difficult reductions. The protonated derivatives generated by the addition of TFA to the macrocycles in CHCl₃ showed distinct colour changes with significant bathochromic shifts in absorption bands. DFT optimized structures of one of the [16]thiatriphyrins and its protonated derivative revealed that the thiophene ring was almost perpendicular whereas the two pyrrole rings were almost in plane with the mean plane defined by the five meso-carbons and TD-DFT studies were in agreement with the experimental observations.