Phenylene-linked cyclotrimer (3T) and cyclotetramer (4T) have been synthesized via Lewis acid-catalyzed selfcondensation of appropriate precursors. Structural and Density Functional Theory (DFT) studies reveal the disruption of annulenic conjugation in both 3T and 4T by linking phenylene rings prevented them from global antiaromaticity. The single crystal X-ray structure of 4T reveals all the nitrogens are pointing toward the macrocyclic core with near-planar and square-shaped geometry, thus in sharp contrast to the ring-strained conformation of 3T.

Acid-catalyzed condensation of a newly prepared di-m-benzipentapyrrane with appropriate mono- and diheterocyclic dialcohols selectively produced stable di-m-benzihexaphyrins and di-m-benziheptaphyrins with only two meso-carbon bridges. Single-crystal X-ray diffraction analyses reveal planar conformation with slight distortion of bridged phenylene rings. Despite the presence of m-phenylene units interrupting the global delocalization, the presence of bithiophene units in di-m-benziheptaphyrins 3a–b exhibits altered optical features covering the entire visible region (ca. 250–720 nm), exhibiting a black dye property as a “metal-free” porphyrinoid.

In this study, we have prepared new tripyrranes embedded with azulene bearing two meso-pentafluorophenyl substituents. They were obtained as diastereomers in high yield which were separated using conventional column chromatography. Their distinct solution structures were unambiguously confirmed by NMR and mass analysis. Our synthetic strategy is simple and straightforward due to the reactivity of 1,3-positions of azulene, which underwent Lewis acid-catalyzed condensation with pyrrole-2-carbinol. These diastereomers were further subjected to acid-catalyzed (CF3COOH) condensation with pyrrole dicarbinol to afford the target N-confused azuliporphyrin (reduced form) in trace amount. However, we obtained the tris-meso-pentafluorophenyl substituted azulicorrole (AzCorA) as major product due to an unprecedented scrambling of the azulitripyrranes. The structural characterization of newly synthesized key precursors and macrocycles was done with the aid of high-resolution mass analyses, and 1H and 2D NMR analyses. The single crystal X-ray structure obtained for AzCorA revealed that the azulene subunit is tilted by 34.03[Formula: see text] due to the steric congestion of inner-NHs.

A simple non-rigid precursor termed as a “triheterole” comprising of 2,2[Formula: see text]-bithiophene linked to [Formula: see text]-pyrrole was prepared using a four-step synthetic strategy. This functionalized triheterole was allowed to undergo acid catalyzed condensation in the presence of Lewis acid (BF3 [Formula: see text] Et2O) to produce the [3 + 3 + 3] cyclotrimer 1 as a major product with trace formation of its higher homologues. Electronic absorption spectrum of 1exhibited a characteristic band (520 nm) and broad band in the visible region. Upon protonation, significant bathochromic shift of the band (608 nm) and the broad band towards near-IR region (ca.1250 nm) indicates its antiaromatic (4[Formula: see text] conjugated circuit. Detailed structural analyses using temperature-dependent 1D and 2D NMR along with DFT level theoretical investigations indicate that the molecule exhibits weak antiaromaticity due to its large fluxional nature.

Two confor matio nal ly di ff er en t [ 26]rubyrin(1.1.0.1.1.0) macrocycles with varying heteroatoms (S/O) and their bis-BODIPYs are reported. The solid-state structure confirms O 2 N 4 with fairly planar pyrrole-inverted conformation, whereas a thiophene-inverted structure for S 2 N 4 is observed. Such conformational differences can also be clearly realized from their spectral and optical features. Upon BF 2 complexation, both rubyrins led to their respective bis-BODIPYs where S 2 N 4 -BOD displayed a perfectly planar conformation as evident from its X-ray structure.