Synthesis and Studies of Stable Nonaromatic Dithia Pyribenzihexaphyrins.

We report here one of the rare examples of expanded hexaphyrins named as dithia pyribenzihexaphyrin macrocycles containing six-membered rings such as pyridine and -phenylene along with five-membered heterocycles such as pyrrole and thiophene as a part of a macrocyclic frame. Trifluoroacetic acid catalyzed [3 + 3] condensation of equimolar mixture of [10,10'-(--butyl phenyl)hydroxymethyl]-1,3-(2-thienyl)pyridine diol (2,6-pyri diol) and 1,4-(phenyl(1-pyrrol-2-yl)methyl)benzene (-benzidipyrrane) in CHCl followed by oxidation with DDQ afforded stable nonaromatic dithia 2,6-pyri--benzihexapyrins and in 6-8% yields. The macrocycles were characterized by high-resolution mass spectroscopy and 1D and 2D NMR spectroscopy. NMR studies revealed the nonaromatic nature of dithia 2,6-pyri--benzihexaphyrins and indicated that the -phenylene ring prefers to be in quininoid form rather than in benzenoid form. The macrocycles displayed sharp absorption bands in the region of ∼380-500 nm and a broad band at ∼700 nm, reflecting their nonaromatic nature. Upon protonation, these macrocycles showed NIR absorption properties. The redox studies of macrocycles indicated their electron-deficient nature. The DFT/TD-DFT studies are in line with the experimental observations.