m-Benziporphyrin(1.1.0.0)s as a Rare Example of Ring-Contracted Carbaporphyrins with Metal-Coordination Ability: Distorted Coordination Structures and Small HOMO-LUMO Gaps

A Janus carbaporphyrin pseudo-dimer

Carbaporphyrin dimers, investigated for their distinctive electronic structures and exceptional properties, have predominantly consisted of systems containing identical subunits. This study addresses the associated knowledge gap by focusing on asymmetric carbaporphyrin dimers with Janus-like characteristics. The synthesis of a Janus-type carbaporphyrin pseudo-dimer 5 is presented. It displays antiaromatic characteristics on the fused side and nonaromatic behavior on the unfused side. A newly synthesized tetraphenylene (TPE) linked bis-dibenzihomoporphyrin 8 and a previously reported dibenzo[g,p]chrysene (DBC) linked bis-dicarbacorrole 9 were prepared as controls. Comprehensive analyses, including 1H NMR spectral studies, single crystal X-ray diffraction analyses, and DFT calculations, validate the mixed character of 5. A further feature of the Janus pseudo-dimer 5 is that it may be transformed into a heterometallic complex, with one side coordinating a Cu(III) center and the other stabilizing a BODIPY complex. This disparate regiochemical reactivity underscores the potential of carbaporphyrin dimers as versatile frameworks, with electronic features and site-specific coordination chemistry controlled through asymmetry. These findings position carbaporphyrin dimers as promising candidates for advances in electronic structure studies, coordination chemistry, materials science, and beyond.

Nanographene-Fused Expanded Carbaporphyrin Tweezers

A nanographene-fused expanded carbaporphyrin (5) and its BF2 complex (6) were synthesized. Single-crystal X-ray structures revealed that 5 and 6 are connected by two hexa-peri-hexabenzocoronene (HBC) units and two dipyrromethene or BODIPY units, respectively. As prepared, 5 and 6 both show nonaromatic character with figure-of-eight carbaoctaphyrin (1.1.1.0.1.1.1.0) cores and adopt tweezers-like conformations characterized by a partially confined space between the two constituent HBC units. The distance between the HBC centers is >10 Å, while the dihedral angles between the two HBC planes are 30.5 and 35.2° for 5 and 6, respectively. The interactions between 5 and 6 and fullerene C60 were studied both in organic media and in the solid state. Proton NMR spectral titrations of 5 and 6 with C60 revealed a 1:1 binding mode for both macrocycles. In toluene-d8, the corresponding binding constants were determined to be 1141 ± 17 and 994 ± 10 M-1 for 5 and 6, respectively. Single-crystal X-ray diffraction structural analyses confirmed the formation of 1:1 fullerene inclusion complexes in the solid state. The C60 guests in both complexes are found within triangular pockets composed of two HBC units from the tweezers-like receptor most closely associated with the bound fullerene, as well as an HBC unit from an adjacent host. Femtosecond transient absorption measurements revealed subpicosecond ultrafast charge separation between 5 (and 6) and C60 in the complexes. To the best of our knowledge, the present report provides the first example wherein a nanographene building block is incorporated into the core of a porphyrinic framework.

Structural isomers of di-p-benzidithiaoctaphyrins

The cis and trans structural isomers of di-p-benzidithiaoctaphyrins were synthesized by adopting two different synthetic routes using readily available precursors under acid-catalyzed conditions, and the isomers were separated using basic alumina column chromatography. 1D and 2D NMR spectroscopy were used to deduce the molecular structures of the macrocycles, which also helps to differentiate the cis isomer from the trans isomer. DFT studies revealed that both the cis and trans isomers adopt figure of eight conformations but exhibit clear differences in their structural features, and the trans isomer is more distorted than the cis isomer. Experimental and theoretical studies revealed that both the cis and trans isomers are nonaromatic stable macrocycles and show subtle differences in their structure, spectral and redox properties. The cis and trans isomers of di-p-benzidithiaoctaphyrin exhibit nonaromatic absorption features in the visible-NIR region, and electrochemical studies revealed their electron-rich nature. TD-DFT studies are in agreement with the experimental observations.

Doubly N-confused and ring-contracted [24]hexaphyrin Pd-complexes as stable antiaromatic N-confused expanded porphyrins

As isomers of the regular porphyrins, N-confused porphyrins have attracted extensive attention of chemists because of their unique chemical structures, chemical reactivities, and physical properties, which result in their promising applications in the fields of catalytic chemistry, biochemistry and material science. Typically, N-confused porphyrins are synthesized via acid catalyzed condensation and following oxidation during which lactams are often formed as the byproducts. Here we report doubly N-confused and ring-contracted [24]hexaphyrin(1.1.0.1.1.0) mono- and bis-Pd-complexes as stable antiaromatic N-confused expanded porphyrins, which are synthesized through Pd-catalyzed Suzuki-Miyaura coupling of 1,14-dibromotripyrrin. These macrocycles show a paratropic ring currents, an ill-defined Soret band, a red-shifted weak absorption tail, and a small HOMO-LUMO gap. NBS bromination of the bis Pd-complex give its mono- and dibromides regioselectively, which are effectively used to synthesize a [24]hexaphyrin dimer and a NiII porphyrin-[24]hexaphyrin-NiII porphyrin triad, respectively.