Revisiting the intense NIR active bronzaphyrin, a 26-π aromatic expanded porphyrin: synthesis and structural analysis.

Dithiabronzaphyrin, with intense absorption and fluorescence in the NIR region, was synthesized as its ß-octaethyl analogue via a thiophene bridged terpyrrole. Solid state structural characterization obtained for the first time revealed inversion of the thiophene rings. Studies showed that there is no effect from protonation or temperature on the structural rigidity of the macrocycle. Crystal packing revealed four open dimeric trifluoroacetate [(CF3COO)2H]- moieties binding to the macrocycle in the protonated form via H bonding.