Twists and Loops: Exploring Lemniscular Vinylogous Benzioctaphyrin(2.0.1.0.2.0.1.0)

Octaphyrins, offer unparalleled opportunities for designing complex molecular architectures with distinct physical and chemical properties. However, lemniscate-shaped benzioctaphyrins remain scantily explored, leaving a gap in understanding how this unconventional geometry/shape influences macrocyclic behaviour. In this study, we explore the design, synthesis, and structural properties of benzioctaphyrin by incorporating the bis-E-stilbene unit, where a vinylene π-bridge connects phenylene rings. The benzioctaphyrin(2.0.1.0.2.0.1.0) adopts a lemniscate topology to alleviate steric strain, with protonation inducing conformational desymmetrization. The presence of a meta-phenylene unit thwarts the global π-conjugation, rendering the macrocycle nonaromatic. Notably, this work represents the first exploration of the oligomeric vinylene group in benzioctaphyrin framework. It offers new insights into how structural modifications influence topology, π-electron delocalization, and macrocyclic flexibility, setting the stage for future advancements in topologically unique porphyrinoid systems.

Tailor-made aromatic porphyrinoids with NIR absorption

The highlight of this article is the recent progress in the state-of-the-art synthetic design and isolation of artificial porphyrinoids by swapping pyrrole component(s) with diverse functionalized pyrrolic(heterocyclic)/carbacycle building block(s) to compare the impact on the electronic absorption spectra and aromaticity of the incorporated isomeric/expanded porphyrinoids. Attention has been directed towards five distinct criteria of utilizing functionalized pyrrolic(heterocyclic)/aromatic hydrocarbons as synthons for NIR absorbing aromatic isomeric (N-confusion)/expanded porphyrinoids (with five/six heterocycles): (i) fused or annelated pyrrole (heterocycle), (ii) functionalized bi-pyrrole/bi-thiophene/bi-furan building blocks, (iii) azulene based carbacycle building block, (iv) vinylogous aromatic carbacycle/heterocycle(s) building block and (v) N-confused pyrrole ring(s), and N-confused fused pyrrole ring(s) leading to π-extension. These hybrid porphyrinoids are ideal candidates for basic research into macrocyclic aromaticity and for many potential applications owing to NIR absorption.