Synthesis and Properties of Nonaromatic meso‐fused Heterobenzihomoporphyrin(2.1.1.1)s

Abstract

Fluorene‐based tripyrrane has been used as a fused precursor to synthesize three novel examples of nonaromatic meso‐fused thia and selenabenzihomoporphyrin(2.1.1.1)s by condensing it with appropriate 2,5‐bis(hydroxymethyl)aryl thiophene or selenophene under acid catalyzed conditions. The meso‐fused heterobenzihomoporphyrins contain one fluorene unit, two pyrrole rings and one thiophene/selenophene ring connected via five meso‐carbons in the macrocyclic framework. The macrocycles were thoroughly characterized by HR‐MS, 1D and 2D NMR, absorption, cyclic voltammetry and DFT/TD‐DFT studies. NMR, absorption, and DFT studies indicated the nonaromatic nature of meso‐fused heterobenzihomoporphyrins. The macrocycles displayed one intense band at ∼380 nm along with a shoulder band at 450 nm and a broad band in the region of 590–850 nm which were bathochromically shifted in the monoprotonated derivatives and absorbed prominently in the NIR region with the peak maxima at ∼1035 nm. The electrochemical studies revealed that the macrocycles showed three well‐defined oxidations and reductions, and TD‐DFT studies corroborated experimental observations.

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“…Later, in 2023, the same group 50 reported the synthesis of nonaromatic meso -fused heterobenzihomoporphyrin(2.1.1.1)s 110a–c (Scheme 20). Fluorene-based tripyrranes 114a–b were condensed with appropriate 2,5-bis(hydroxymethyl)aryl thiophenes/selenophene 39b / 39c / 40 under acid-catalyzed conditions to afford meso -fused heterobenzihomoporphyrin(2.1.1.1)s 110a–c in 3–4% yields.…”