Expanded Fused Trithiaporphyrins‐Synthesis, Structure, and Properties

Abstract Expanded fused trithiaporphyrins with S 3 N inner core were synthesized by treating the appropriate new tetrapyrrane mono‐ol with BF 3 ∙OEt 2 under inert atmosphere followed by DDQ oxidation. The condensation was expected to form expanded trithiaporphyrin but during condensation, one of the thiophene rings was inverted and β ‐carbon of inverted thiophene ring was involved in bonding with pyrrole N to generate the fused tripentacyclic moiety inside the porphyrinoid. The condensation also resulted in the formation of calix trithiaporphyrin with one sp 3 meso ‐carbon which gets converted to expanded fused trithiaporphyrin upon treatment with trifluoroacetic acid. Two expanded fused trithiaporphyrins and one expanded calix trithiaporphyrin were synthesized, characterized, and studied by 1D & 2D NMR spectroscopy, X‐ray crystallography for one expanded fused trithiaporphyrins, absorption spectroscopy, cyclic voltammetry, and DFT/TD‐DFT techniques. The X‐ray structure of expanded fused trithiaporphyrin revealed that the macrocycle adopts angular shape and fused tripentacyclic ring deviates by 27.85° from mean plane to reduce the steric congestion inside the macrocyclic core. The expanded fused trithiaporphyrin and calix trithiaporphyrin showed different absorption features and absorbs in the region of 250–700 nm. The electrochemical studies revealed that the expanded fused trithiaporphyrins were electron‐rich and undergo easier oxidations. DFT/TD‐DFT studies were in agreement with experimental observations.