Synthesis and structural studies of an 11,12-dihydroindolo[2,3-a]-carbazole embedded macrocycle with inverted furan exhibiting NIR-I absorption upon protonation

An acid-catalyzed condensation of a functionalized indolo[2,3a]carbazole with furan dicarbinol resulted in the formation of donor-acceptor-based polyaromatic embedded porphyrinoid InCF. The NMR, along with UV-visible spectral studies, confirms the formation of InCF and redox properties are investigated by electrochemical studies. The InCF exhibits panchromatic absorption, and upon protonation, it showed absorption reaching up to the near-IR region. Intriguingly, the crystal structure revealed the presence of an inverted furan, which is inclined outward from the macrocyclic plane. Further, TD-DFT calculations at level of B3LYP/6-31G(d,p) were performed to determine the HOMO and LUMO levels, revealing the HOMO is localized on the indolocarbazole unit, while that of LUMO is primarily distributed over the remaining part of the macrocycle, including the azafulvene and furan moieties. The NICS(0) values show the non-aromaticity of InCF.