Expanded Carbaporphyrinoids

Porphyrinoid framework embedded with polycyclic aromatic hydrocarbons: new synthetic marvels

The highly conjugated tetrapyrrolic porphyrin macrocycle and its contracted and expanded congeners have been extensively used for a wide range of applications across diverse research domains because of their captivating and intriguing features. Over the years, the porphyrin framework and electronic properties of porphyrinoids have been modified and tuned by replacing one or more pyrrole ring(s) with five- and six-membered heterocycles/carbacycles, and their resulting properties have been explored. In recent times, polycyclic aromatic hydrocarbons (PAHs), such as biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, fluorene, pyrene and dibenzo[g,p]chrysene, have been used to replace one or more pyrrole rings of porphyrinoids, and resulting polycyclic-aromatic-embedded porphyrinoids show unique features that differ from those of other modified porphyrinoids. The polycyclic aromatic hydrocarbons in the porphyrinoid macrocyclic framework induce different π-conjugation pathways in macrocycles, exhibit variable degrees of aromaticity from nonaromatic to aromatic and antiaromatic and provide a unique ligand environment to form stable coordination and organometallic complexes in which metals show uncommon oxidation states and unusual reactivity. This review presents an overview of the synthesis, coordination chemistry, structure and properties of various porphyrinoids with an embedded PAH that have been reported to date.

21-Carba-23-selenaporphyrinoid Dyads-An Azepine Unit as a Merging Motif

The oxidation of 10,15-diaryl-21-carba-23-selenaporphyrinoids resulted in the creation of dyads. The dimerization process follows a [5+2] cycloaddition path with the formation of an azepine unit. The arrays display two direct bonds between the peripheral carbocyclic carbon atoms of one carbaselenaporphyrinic subunit and the central carbon and nitrogen atoms of the second subunit. This results in a unique canted arrangement of two carbaporphyrinoid planes resembling an open seashell-like motif.

Dibenzi Heteroheptaphyrin(2.0.1.1.1.1.0)s: Synthesis, Spectral, Redox and Theoretical Studies

Three examples of dibenzi heteroheptaphyrin(2.0.1.1.1.1.0)s were synthesized by condensing bis(phenylene ethene) based hexapyrrane with appropriate diol, 2,5-bis(α-hydroxy-α-arylmethyl) thiophene or selenophene in CH2 Cl2 under BF3  ⋅ OEt2 catalyzed inert atmosphere conditions followed by DDQ oxidation in open air. HR-MS analyses confirmed the identities of dibenzi heteroheptaphyrins. The DFT optimized structures revealed that dibenzi heteroheptaphyrins were highly distorted nonplanar macrocycles with two thiophene rings preferred to be in an inverted conformation. 1D & 2D NMR helped in deducing the molecular structures of dibenzi heteroheptaphyrins and supported their nonaromatic nature. The theoretical NMR calculations were carried which matched closely with the experimental NMR data. NMR studies also revealed that the π-delocaliztion was significantly altered in dibenzi heteroheptaphyrins compared to previously reported dibenzi hexaphyrins. The dibenzi heptaphyrins showed one sharp absorption band in 400-500 nm region and a broad band in the region of 600-800 nm which were bathochromically shifted in their diprotonated derivatives. The theoretical absorption calculations corroborate the slight hypsochromic shift of the broad absorption band in the lower energy region of dibenzi heptaphyrins compared to dibenzi hexaphyrins. The electrochemical studies revealed that the dibenzi heptaphyrins were easier to reduce but difficult to oxidize compared to dibenzi hexaphyrins.

Resolution of Expanded Porphyrinoids: A Path to Persistent Chirality and Appealing Chiroptical Properties

Chirality is a fundamental characteristic of nature. Expanded porphyrinoids and their analogues offer an attractive platform for delving into the intricacies of chirality. Expanded porphyrinoids comprise pyrrolic macrocycles and related heterocyclic systems. As a class, expanded porphyrinoids are widely recognized for their flexible structural features, nontrivial coordination capabilities, and intriguing optical and electronic properties. With limited exceptions, their inherent conformational flexibility coupled with a low racemization barrier allows for the facile interchange between enantiomers. As a result, achieving the effective chiral resolution of individual enantiomers and the subsequent exploration of their chiroptical properties represents a significant challenge. This review summarizes strategies used to realize the chiral resolution of expanded porphyrinoids and the understanding of intrinsic chiroptical properties that has emerged from these separation efforts. It is our hope that this review will serve not only to codify our current understanding of chiral expanded porphyrinoids, but also inspire advances in the generalized area of chiral functional materials.

Tying a knot between crown ethers and porphyrins

Porphyrins and crown ether hybrids have emerged as a promising class of molecules composed of elements of a tetrapyrrole macrocycle and an oligo(ethylene glycol) segment. These hybrid systems constitute a broad group of compounds, including crowned porphyrins, crownphyrins, and calixpyrrole-crown ether systems forming Pacman complexes with transition metals. Their unique nature accustoms them as excellent ligands and hosts capable of binding guest molecules/ions, but also to undergo unusual transformations, such as metal-induced expansion/contraction. Depending on the design of the particular hybrid, they present unique features involving intriguing redox chemistry, interesting optical properties, and reactivity towards transition metals. In this perspective article, the overview of both the early designs of porphyrin-crown ether hybrids, as well as the most recent advances in the synthesis and characterisation of this remarkable group of macrocyclic systems, are addressed. The discussion covers the strategies employed in synthesising these systems, including cyclisation reactions, self-assembly, and their remarkable reactivity. The potential applications of porphyrin-crown ether hybrids are also highlighted. Moreover, the discussion identifies the challenges associated with synthesising and characterising hybrids, outlining the possible future directions.

Advent and features of pyriporphyrinoids: an overview of a pyridine-based porphyrin analogue

Pyriporphyrinoids have recently attracted a significant proliferation of attention due to their versatile characters, which stem from structural motifs in which the pyridine moiety is involved. The evolution of pyriporphyrin chemistry revealed the subtle modifications of the macrocyclic core that tweak the electronic structure as compared to the parental macrocycle. The amendment of π-electronic organization inside the core manifests exceptional photophysical and coordination properties that cover a vast range of seemingly contradictory fields. In fundamental chemistry, the pyridine unit acts as a modulator of π-conjugated porphyrinoid systems, resulting in aromaticity swapping. From the applied chemistry perspective, these macrocycles are primarily utilized as (i) sensors, (ii) NIR absorbing photoacoustic dyes, (iii) electrochemical catalysts, (iv) singlet biradicaloid generation and (v) contributors to generate metal complexes with intriguing binding modes. Surprisingly, despite their prominence, pyriporphyrinoids are inadequately investigated, while pyridine unit-embedded calixphyrin, calixpyridinopyrrole and calixpyridine are barely reported. This review article illustrates the controlled formation of specific porphyrinic scaffolds with pyridine unit(s) and diverse functionalized heterocyclic and/or carbocyclic building block(s), and demonstrates a substantial influence on the macrocyclic properties.

Phenanthrene-Incorporated Isoamethyrin: A Near-Planar Macrocycle That Display Enhanced Aromaticity via Protonation-Triggered Conformation Changes

Controlling the aromaticity in expanded porphyrins is a forefront research topic, and the strategy of using protonation-triggered conformational changes to fine-tune electronic properties and aromaticity has yet to be generalized in rigid and planar expanded porphyrins. Here, we synthesized phenanthrene-incorporated isoamethyrins that possess near-planar conformations and nonaromatic characters. However, when methanesulfonic acid (MSA) was added, geometric deformations occurred to minimize the unfavorable strain, resulting in macrocycles that were weakly aromatic as a whole.

Synthesis, Spectral, Redox and Theoretical Studies of Stable Nonaromatic Dicarba Dithia Hexaphyrin(2.0.1.1.1.0)s with Two Inverted Thiophenes

A series of dicarba dithia hexaphyrin(2.0.1.1.1.0)s containing two p-phenylene rings, two thiophene rings, and two pyrrole rings connected via five meso carbons were synthesized by condensing the key precursor, hexapyrrane, which was prepared over a sequence of steps, with the appropriate aromatic aldehyde under acid catalytic conditions followed by alumina chromatographic purification. Detailed one-dimensional (1D) and two-dimensional (2D) NMR studies revealed that the two thiophene rings were inverted and facing outward from the macrocyclic core. Interestingly, one of the inverted thiophene rings adopts a normal orientation in the protonated derivatives of macrocycles generated by addition of trifluoroacetic acid to the appropriate macrocyclic solution. The spectroscopic studies support the non-aromatic nature of macrocycles, and the macrocycles exhibit a distinct sharp band at ∼425 nm along with a broad band in the range of 550-1000 nm, which experienced a red shift with a clear color change in the protonated derivatives. The redox studies showed lower oxidation potentials, indicating their electron-rich nature. The density functional theoretical (DFT) studies showed that the hexaphyrins adopt oval-shaped structures, and time-dependent-DFT (TD-DFT) studies parallelly matched the experimental observations of macrocycles.

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

The unique environment within the core of carbaporphyrinoid systems provides a platform to explore unusual organometallic chemistry. The ability of these structures to form stable organometallic derivatives was first demonstrated for N-confused porphyrins but many other carbaporphyrin-type systems were subsequently shown to exhibit similar or complementary properties. Metalation commonly occurs with catalytically active transition metal cations and the resulting derivatives exhibit widely different physical, chemical and spectroscopic properties and range from strongly aromatic to nonaromatic and antiaromatic species. Metalation may trigger unusual, highly selective, oxidation reactions. Alkyl group migration has been observed within the cavity of metalated carbaporphyrins, and in some cases ring contraction of the carbocyclic subunit takes place. Over the past thirty years, studies in this area have led to multiple synthetic routes to carbaporphyrinoid ligands and remarkable organometallic chemistry has been reported. An overview of this important area is presented.

Anthracene-Fused Oligo-BODIPYs: A New Class of π-Extended NIR-Absorbing Materials

Large π-conjugated systems are key in the area of molecular materials. Herein, we prepare via Au^I -catalyzed cyclization a series of fully π-conjugated anthracene-fused oligo-BODIPYs. Their structural and optoelectronic properties were studied by several techniques, ranging from X-ray, UV/Vis, and cyclic voltammetry to transient absorption spectroscopy. As a complement, their electronic structures were explored by means of Density Functional Theory (DFT) calculations. Depending on the size and shape of the π-conjugated skeleton, unique features-such as face-to-face supramolecular organization, NIR absorption and fluorescence as well as strong electron accepting character-were noted. All in all, the aforementioned features render them valuable for technological applications.

Di-2,7-pyrenidecaphyrin(1.1.0.0.0.1.1.0.0.0) and Its Bis-Organopalladium Complexes: Synthesis and Chiroptical Properties

A non-aromatic expanded carbaporphyrinoid, incorporating two built-in 2,7-pyrenylene moieties was synthesized. The intrinsically labile structure was demonstrated by proton-triggered conformational changes between the figure-of-eight and quasi-Möbius conformers. Upon treatment with Pd(OAc)₂ , the reaction produces two bis-Pd^II complexes with distinct coordination modes. Metal coordination serves to fix the macrocyclic frameworks with the net result that both bis-Pd^II complexes could be resolved by high performance liquid chromatography (HPLC) on a chiral stationary phase. The isolated enantiomers showed persistent chiroptical properties as evidenced by the intense response in the circular dichroism (CD) spectra and the record high absorption dissymmetry factors (g_abs of up to 0.038) seen in the near-infrared spectral region. Moreover, the mutual interconversion of these two Pd^II complexes was found to be stereospecific and to favor the more stable isomers under weakly acidic conditions.

Rh(I) and Organo-Rh(III) Complexes of meso-Triarylbiphenylcorrole

Rhodium complexes of biphenylcorrole are reported, and the molecular structures of the complexes are unambiguously confirmed by single-crystal X-ray analysis. The adj-CCNN core of the dicarbacorrole efficiently stabilizes a rhodium metal ion in its two different oxidation states. It is pertinent to point out that the Rh(I) metal complex attains square-planar geometry while organo-Rh(III) forms an octahedral complex. Furthermore, density functional theory studies corroborate the experimental findings.

Two-photon absorption of 28-hetero-2,7-naphthiporphyrins: expanded carbaporphyrinoid macrocycles

The one- and two-photon absorption (1PA and 2PA) properties of three expanded aceneporphyrinoids, 28-thia-, 28-selena- and 28-tellura-2,7-naphthiporphyrin, have been studied. The open-aperture Z-scan technique was used to determine two-photon absorption cross-sections in the near infrared range using an amplified femtosecond laser system. The maximum values of the cross sections were found to be 99, 200 and 650 GM at 900 nm and 1, 13 and 31 GM at 1400 nm for the three investigated compounds, respectively. These results demonstrate enhanced 2PA properties compared with well-known porphyrin photosensitizers, such as Foscan®, showing the potential of porphyrin core modification for optimizing infrared nonlinear absorbers.

The one- and two-photon absorption (1PA and 2PA) properties of three expanded aceneporphyrinoids, 28-thia-, 28-selena- and 28-tellura-2,7-naphthiporphyrin, have been studied.

Synthesis and Studies of Structural Isomers of meso-Fused Dicarbahexaphyrins

Two close structurally related isomers of nonaromatic meso -fused dicarbahexaphyrins were synthesized by condensing one equivalent of fluorene based tripyrrane with one equivalent of pentafluorobenzaldehyde in CH 2 Cl 2 under BF 3 .OEt 2 catalyzed conditions. The cis and trans isomers of meso -fused dicarbahexaphyrins were separated by preparative thin-layer chromatography and isolated pure macrocycles as green solids in 6-7% yields. NMR spectra of cis and trans isomers are quite distinct from each other and trans isomer was very symmetric and showed fewer resonances than cis isomer in NMR. The NMR study supported the nonaromatic nature of both cis and trans isomers of meso -fused dicarbahexaphyrins. DFT optimized structures revealed that the cis isomer adopted a singly twisted puckered conformation whereas the trans isomer displayed a saddle like conformation. Both cis and trans isomers almost showed similar nonaromatic absorption features with slight differences in their peak maxima. However, the protonated derivative of cis isomer showed absorption bands in visible-NIR region with bands extended upto 1000 nm whereas the trans isomer showed strong bands in the visible region. Both cis and trans macrocycles were easier to oxidize and reduce and TD-DFT studies corroborated with the experimental findings.

3,6-Carbazoylene Octaphyrin (1.0.0.0.1.0.0.0) and Its Bis-BF2 Complex

3,6-Carbazole precursors were used to prepare an octaphyrin. The conformation and electronic structure of the system could be modulated through trifluoroacetate (TFA) protonation and BF₂ complexation. The resulting nonaromatic macrocyclic complexes, 2-2TFA and 2-2BF₂, displayed noteworthy photophysical properties. For instance, the diprotonated species 2-2TFA showed a strong panchromic absorption up to 800 nm, while the bis-BF₂-chelated dipyrromethene (BODIPY)-like complex 2-2BF₂ exhibited an intense visible absorption feature (ε_535nm = 2.1 × 10⁵ M^-1 cm^-1), as well as a relatively red-shifted emission at 640 nm characterized by a large Stokes shift. It was found that 2-2BF₂ could be used to construct a high-quality organic microlaser that functions under optical pumping. The present study highlights the potential utility of expanded porphyrins as possible laser dyes.

1,4-Phenylene-Incorporated Decaphyrin(1.0.1.0.0.1.0.1.0.0): Synthesis, Structure, and Topological Chirality

Expanded porphyrins represent emerging structures in realizing topological chirality; however, their inherent flexibility has hampered the effective chiral resolution. Herein, we rationally designed a decaphyrin 9, which could be separated into its enantiomers in the free-base form. The enantiomers showed noteworthy chiroptical properties, e.g., the intense circular dichroism response in the visible spectrum, and high absorption dissymmetry factors (g_abs) of 0.036 at 618 nm. Theoretical analyses further explained the origin of the high g_abs value.

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Bis-(Fluorene)-Embedded Hexaphyrins

The polyaromatic hydrocarbon containing expanded porphyrins, bis-(fluorene)-embedded hexaphyrins, were synthesized by condensing fluorene-based tripyrrane with pentafluorobenzaldehyde in CH₂Cl₂ in the presence of 1 equiv of BF₃·OEt₂ under an inert atmosphere followed by oxidation with DDQ in open air at room temperature. The reaction worked only when 1 equiv of BF₃·OEt₂ was added to the reaction mixture under concentrated reaction conditions. The bis-(fluorene)-embedded macrocycles were characterized and studied by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), absorption, electrochemical, and density functional theory (DFT)/time-dependent (TD)-DFT techniques. In ¹H NMR, the hexaphyrins showed a few broad unresolved resonances at room temperature, but the NMR spectra were well-resolved at lower temperatures, indicating that the hexaphyrins were very flexible. The DFT-optimized structures indicated that the two fluorene units at the crossing point of the figure-eight loop makes an angle of ∼79.73° with each other, the fluorene moieties maintained their own planarity, and one of the fluorene moieties was not involved in conjugation with the rest of the macrocycle. The absorption spectra of hexaphyrins showed one intense sharp band in the higher energy region and a broad band in the lower energy region. The electrochemical studies indicated that expanded hexaphyrins are relatively electron-rich and showed three easier oxidations and one reduction. The DFT/TD-DFT studies are in agreement with the experimental observations.

Phenanthrene cyclocarbonylation – Core post-synthetic modification of phenanthriporphyrin

The unique [Fe(CO)5]-induced cyclocarbonylation of the phenanthriporphyrin's core is an intriguing example of a post-synthetic core modification of the macrocycle. The reaction involves the activation of C(22)−H and C(25)−H bonds,...

Kinetic trapping of a cobalt(ii) metallocage using a carbazole-containing expanded carbaporphyrinoid ligand

The meso-unsubstituted expanded porphyrinoid 3, incorporating two carbazole moieties, acts as an effective ligand for Co(ii) and permits the isolation and X-ray diffraction-based characterization of a 6 : 3 metal-to-ligand metallocage complex that converts spontaneously to the constituent 2 : 1 metal-to-ligand metalloring species in chloroform solution. The discrete metalloring is formed directly when the Co(ii) complex is crystallized from supersaturated solutions, whereas crystallization from more dilute solutions favors the metallocage. Studies with two other test cations, Pd(ii) and Zn(ii), revealed exclusive formation of the monomeric metalloring complexes with no evidence of higher order species being formed. Structural, electrochemical and UV-vis-NIR absorption spectral studies provide support for the conclusion that the Pd(ii) complex is less distorted and more effectively conjugated than its Co(ii) and Zn(ii) congeners, an inference further supported by TD-DFT calculations. The findings reported here underscore how expanded porphyrins can support coordination modes, including bimetallic complexes and self-assembled cage structures, that are not necessarily easy to access using more traditional ligand systems.

Carbazole containing expanded carbaporphyrinoid ligand supports the formation of 2 : 1 metal-to-ligand complexes with Pd, Co, and Zn. Solid-state studies also revealed formation of a 6 : 3 metal-to-ligand metallocage in the case of Co complexation.

Recent Advances in the Design and Syntheses of Porphyrinoids by Embedding Higher Analogues of Arene and Pyridine Units

Due to enthralling applications in various fields and augmenting fundamental wisdom, π-conjugated macrocycles in general and porphyrin systems in particular are constantly explored. Subtle modifications of porphyrin structure can amend the rudimentary properties. Pursuing innovative properties provides impetus to underpin arene or pyridine moiety embedded porphyrin derivatives. There have been several reviews related to arene incorporated carbaporphyrinoids; however, recent developments of porphyrin analogues by introducing higher analogues of arenes and pyridine units are not adequately inspected. This mini-review mainly focuses on biphenyl, bipyridine, terphenyl, and mixed arene pyridine embedded porphyrin analogues and their coordination chemistry.

Synthesis of Non- or Antiaromatic Dicarbaamethyrin: [24]Diazulihexaphyrin(0.1.0.0.1.0)

A "3+3" condensation reaction of 1,3-di(2-pyrrolyl)azulene with aryl aldehyde followed by an oxidative aromatization afforded diazuliamethyrin, [24]diazulihexaphyrin(0.1.0.0.1.0). X-ray diffraction analysis revealed a relatively planar structure of diprotonated diazuliamethyrin with a mean plane deviation of 0.37 Å. A 24π non- or antiaromatic character was confirmed by ¹H NMR, absorption, MCD spectra, and TD-DFT calculations that included the NICS values and ACID plots.

Disruption of Antiaromaticity in Structurally Related Expanded Porphyrin-like Macrocycles with Benzene Linkers

1,4-Phenylene-linked cyclotrimer (3T) and cyclotetramer (4T) have been synthesized via Lewis acid-catalyzed self-condensation 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.

Inverted and fused expanded heteroporphyrins

Expanded heteroporphyrins are a class of porphyrin macrocycles containing pyrrole, thiophene, furan, selenophene and other heterocyclic rings that are connected to form an internal ring pathway containing a minimum of 17 atoms and more than 18 delocalized π electrons in their conjugated macrocyclic framework. Considering that expanded heteroporphyrins are large in size, these macrocycles are structurally flexible and prefer to adopt various conformations in which one or more pyrrole(s)/heterocycle(s) tend to be in an inverted conformation and pointed outward from the centre of the macrocyclic core. The inverted expanded heteroporphyrins are divided into two classes as follows: (1) N-inverted expanded heteroporphyrins and (2) hetero-atom inverted expanded heteroporphyrins. Both inverted expanded heteroporphyrins show quite unique features in terms of their structure, aromaticity, and electronic and coordination properties. Sometimes, inverted expanded heteroporphyrins lead to the formation of fused expanded heteroporphyrins because of the intramolecular fusion of the pyrrole "N" with the "C" of the inverted heterocycle ring, which also exhibit unique features compared to inverted expanded heteroporphyrins. In this review, we attempt to describe the synthesis, structure, and aromatic, electronic and coordination properties of inverted and fused expanded heteroporphyrins. This review covers the synthesis, structure and properties of inverted and fused expanded heteroporphyrins containing a combination of pyrrole/heterocycle rings starting with five pyrrole/heterocycle-containing pentaphyrins, and then expanded heteroporphyrins containing six, seven, eight and more pyrrole/heterocyclic rings in their porphyrin macrocyclic framework.

Experimental and Theoretical Evidence for Aromatic Stabilization Energy in Large Macrocycles

Enhanced thermodynamic stability is a fundamental characteristic of aromatic molecules, yet most previous studies of aromatic stabilization energy (ASE) have been limited to small rings with up to 18 π-electrons. Here we demonstrate that ASE can be detected experimentally in π-conjugated porphyrin nanorings with Hückel circuits of 76-108 π-electrons. This conclusion is supported by analyzing redox potentials to calculate the energy change for isodesmic reactions that convert an aromatic ring to an antiaromatic ring or vice versa. It is also supported by analyzing the energy barriers to conformational equilibria that disrupt aromaticity in the transition state. Both types of experiment indicate that cationic porphyrin nanorings display ASEs of 1-5 kJ mol^-1. Density functional theory calculations reproduce the results for both types of experiment and predict ASEs in the range of 1-16 kJ mol^-1. The experimental ASEs in porphyrin nanorings are compared with an experimental ASE of [18]annulene of ∼11 kJ mol^-1, deduced from analysis of the energy barriers to conformational equilibria in [16], [18], and [20]annulene. Calculated energies of isodesmic reactions give an ASE of ∼37 kJ mol^-1 in [18]annulene. This work contributes to a fundamental understanding of aromaticity in large macrocycles.

PtCl2 mediated peripheral transformation of carbatriphyrin(3.1.1) into a meso-fused β-β' dimer and its monomer analogue

An unprecedented formation of a meso-fused β-β' carbaporphyrin dimer and its monomer with a keto group was described. These analogues were synthesized from carbatriphyrin(3.1.1.) by a metal assisted strategy using PtCl2 salt in a single step without any prefunctionalized precursors. Upon dimerization, the monomeric ligand with a dianionic core is transformed into a dimeric structure with unique trianionic cores.

Synthesis, Structure, and Optical Properties of Di-m-benzihexaphyrins (1.1.0.0.0.0) and Di-m-benziheptaphyrins (1.0.1.0.0.0.0): Blackening of m-Phenylene-Linked Dicarbaporphyrinoids by Simple π-Expansion

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.

Isosmaragdyrin with an N3C2 core: stabilization of Rh(i) and organo-Pt(ii) complexes

Isosmaragdyrin with an N₃C₂ core is successfully achieved by introducing a 2,6-di-m-phenylpyridine unit. The core is utilized to stabilize the Rh(i) ion in the N-Rh(i)-N bonding mode and the Pt(ii) ion in the (N^C)N fashion to form an unsymmetrical pincer-type organometallic complex.

Structurally Isomerized Bis-Biphenyl Moieties Embedded in Hexaphyrin(3.1.1.3.1.1) and Octaphyrin(1.1.1.0.1.1.1.0)

An o-p-biphenyl moiety-incorporated 32π hexaphyrin(3.1.1.3.1.1) is successfully achieved. Replacing ortho with meta connectivity in the biphenyl unit of hexaphyrin leads to the formation of its structural isomer, octaphyrin(1.1.1.0.1.1.1.0). Spectral and structural analyses reveal the lack of planarity in hexaphyrin and the presence of an m-arene unit in octaphyrin, thus affording nonaromatic characteristics.