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.

Synthesis and photothermal conversion properties of sandwich N-fused porphyrin rhodium-μ-dichloride dimer complexes: π-extended analog of pentamethylcyclopentadienyl dirhodium(III)-μ-dichloride dimer

Anionic cyclopentadienyl (Cp) and its pentamethyl-substituted derivative (Cp*) serve as crucial ligands for creating stable π-coordinated materials, including catalysts. From a structural perspective, the π-extended analog of Cp, known as an N-fused porphyrin (NFP), is recognized as an intriguing 18π aromatic chromophore, offering near-infrared (NIR) optical properties that can be fine-tuned through metal complexation. When coordinated with rhodium at the central NFP core, it forms a sandwich binuclear rhodium(III) complex along with terminal and bridging chloride ligands, denoted as Rh-1, and its bromo derivative, Rh-1-Br. In contrast to the bis-NFP complex of iron(II) reported previously by our team, both Rh-1 and Rh-1-Br complexes exhibit strong NIR optical properties and narrow HOMO-LUMO energy gaps, attributed to minimal orbital interactions between the two co-facial NFP ligands. Leveraging these NIR absorption properties, we assessed the photothermal conversion properties of Rh-1 and ligand 1, revealing high conversion efficiency. This suggests their potential application as photothermal agents for use in photothermal therapy.

One Pot Synthesis of Two Distinct Macrocycles: Aromatic p-Benzihexaphyrin and Nonaromatic Doubly Fused p-Benzihexaphyrin

Aromatic trithia p-benzihexaphyrins and nonaromatic doubly fused trithia p-benzihexaphyrins were synthesized in a one pot reaction by condensing a p-benzithiophene based tetrapyrrane with three different bithiophene diols under acid catalyzed conditions. The aromatic and nonaromatic macrocycles showed clear differences in colour, NMR, absorption, and electrochemical properties. Theoretical studies supported the observed aromatic and nonaromatic characteristics, respectively, of the p-benzihexaphyrins and their N-fused derivatives.

Tetra S-confused porphyrinoids

Maximum confusion in porphyrinoids can be achieved by inter-linking heterocycles only through 2,4-connectivity. 20π confused porphycene and 30π expanded porphycene represent examples with the highest number of confused heterocyclic units in a given macrocycle. They significantly differ from the parent 20π porphycene and 30π hexaphyrin in their structural, electronic and redox properties due to the cross conjugation arising from the 2,4-connectivity of the heterocycle. They have been characterized by single crystal X-ray diffraction studies and their aromatic features have been substantiated by quantum chemical calculations.

Designing N-Confused Metalloporphyrin-Based Covalent Organic Frameworks for Enhanced Electrocatalytic Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO2 ) into value-added products is promising to alleviate greenhouse gas emission and energy demands. Metalloporphyrin-based covalent organic frameworks (MN4 -Por-COFs) provide a platform for rational design of electrocatalyst for CO2 reduction reaction (CO2 RR). Herein, through systematic quantum-chemical studies, the N-confused metallo-Por-COFs are reported as novel catalysts for CO2 RR. For MN4 -Por-COFs, among the ten 3d metals, M = Co/Cr stands out in catalyzing CO2 RR to CO or HCOOH; hence, N-confused Por-COFs with Co/CrN3 C1 and Co/CrN2 C2 centers are designed. Calculations indicate CoNx Cy -Por-COFs exhibit lower limiting potential (-0.76 and -0.60 V) for CO2 -to-CO reduction than its parent CoN4 -Por-COFs (-0.89 V) and make it feasible to yield deep-reduction degree C1 products CH3 OH and CH4 . Electronic structure analysis reveals that substituting CoN4 to CoN3 C1 /CoN2 C2 increases the electron density on Co-atom and raises the d-band center, thus stabilizing the key intermediates of the potential determining step and lowering the limiting potential. For similar reason, changing the core from CrN4 to CrN3 C1 /CrN2 C2 lowers the limiting potential for CO2 -to-HCOOH reduction. This work predicts N-confused Co/CrNx Cy -Por-COFs to be high-performance CO2 RR catalyst candidates. Inspiringly, as a proof-of-concept study, it provides an alternative strategy for coordination regulation and theoretical guidelines for rational design of catalysts.

Water-soluble anionic N-confused porphyrin for sensitive and selective detection of heavy metal pollutants in aqueous environment

Efficient detection and quantification of metal ions in real time and in a cost-effective manner is a critical step in combating the increasing danger of heavy metal contamination of our biosphere. The potential of water-soluble anionic derivative of N-confused tetraphenylporphyrin (WS-NCTPP) has been investigated for quantitative detection of heavy metal ions. The results show that the photophysical properties of WS-NCTPP differ significantly in the presence of four metal ions, namely Hg(II), Zn(II), Co(II) and Cu(II). The variation in the spectral behaviour is driven by the formation of 1:1 complexes with all the four cations with varied degree of complexation. The selectivity of the sensing is studied through interference studies, indicating maximum selectivity for Hg(II) cations. Computational studies of the structural features of the metal complexes with WS-NCTPP help in establishing the geometry and binding interactions between the metal ions and the porphyrin nucleus. The results demonstrate the promising potential of the NCTPP probe which should be utilized for detection of heavy metal ions, especially mercury, in the near future.

Organometallic chemistry confined within a porphyrin-like framework

The world of modified porphyrins changed forever when an N-confused porphyrin (NCP), a porphyrin isomer, was first published in 1994. The replacement of one inner nitrogen with a carbon atom revolutionised the chemistry that one is able to perform within the coordination cavity. One could explore new pathways in the organometallic chemistry of porphyrins by forcing a carbon fragment from the ring or an inner substituent to sit close to an inserted metal ion. Since the NCP discovery, a series of modifications became available to tune the coordination properties of the cavity, introducing a fascinating realm of carbaporphyrins. The review surveys all possible carbatetraphyrins(1.1.1.1) and their spectacular coordination and organometallic chemistry.

Cyclic Carbaporphyrin Arrays

Two cyclic carbaporphyrin arrays (trimer 6 and tetramer 7) were synthesized from a dibrominated carbaporphyrin precursor (5) via a one-pot Yamamoto-type coupling. Single-crystal X-ray diffraction analyses revealed that 6 and 7 contain three and four covalently linked carbaporphyrin (formally dicarbacorrole) units, respectively. Trimer 6 adopts a roughly planar conformation and tetramer 7 adopts an up-and-down zig-zag conformation. Both 6 and 7 contain a [n]cyclo-meta-phenylene ([n]CMP) core, namely, [6]- and [8]CMP for 6 and 7, respectively. Transient absorption (TA) anisotropy and pump-power-dependent excited-state decay studies provided evidence for excitation energy transfer (EET) within both trimer 6 and tetramer 7. The exciton energy hopping (EEH) times were estimated to be 18 and 35 ps for 6 and 7, respectively, as inferred from pump-power-dependent TA measurements. Since the center-to-center distances between adjacent carbaporphyrin units are similar in 6 and 7, the different EEH times are attributed to differences in the orientation of the transition dipoles in these two congeneric arrays. The orientation factor κ₂, the key parameter defining the Förster resonance energy transfer efficiency, was calculated to be 2.15 and 1.03 for 6 and 7, respectively, a finding that supports the shorter excitation energy hopping time seen in the case of trimer 6. To our knowledge, this is the first time that covalently linked cyclic carbaporphyrin arrays were synthesized using a single carbaporphyrin as the starting point and that EET between carbaporphyrin subunits constrained within a well-defined polycyclic framework has been correlated with structural differences.

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.

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.

Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

The replacement of one or more pyrrolic building block(s) of a porphyrin by a nonpyrrolic heterocycle leads to the formation of so-called pyrrole-modified porphyrins (PMPs), porphyrinoids of broad structural variability. The wide range of coordination environments (type, number, charge, and architecture of the donor atoms) that the pyrrole-modified frameworks provide to the central metal ions, the frequent presence of donor atoms at their periphery, and their often observed nonplanarity or conformational flexibility distinguish the complexes of the PMPs clearly from those of the traditional square-planar, dianionic, N₄-coordinating (hydro)porphyrins. Their different coordination properties suggest their utilization in areas beyond which regular metalloporphyrins are suitable. Following a general introduction to the synthetic methodologies available to generate pyrrole-modified porphyrins, their general structure, history, coordination chemistry, and optical properties, this Review highlights the chemical, electronic (optical), and structural differences of specific classes of metalloporphyrinoids containing nonpyrrolic heterocycles. The focus is on macrocycles with similar "tetrapyrrolic" architectures as porphyrins, thusly excluding the majority of expanded porphyrins. We highlight the relevance and application of these metal complexes in biological and technical fields as chemosensors, catalysts, photochemotherapeutics, or imaging agents. This Review provides an introduction to the field of metallo-PMPs as well as a comprehensive snapshot of the current state of the art of their synthesis, structures, and properties. It also aims to provide encouragement for the further study of these intriguing and structurally versatile metalloporphyrinoids.

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.

Porphyriynes: 18-π-Conjugated Macrocycles Incorporating a Triple Bond

Tetraphenylporphyriyne (Pyne1), a novel porphyrin analogue with a C≡C bond incorporated into an 18-π-conjugated system, has been created via cleavage of the N-confused pyrrolic ring in Ag(III) N-confused tetraphenylporphyrin. The structure of Pyne1 was confirmed by X-ray crystallography and ¹H NMR, IR, and UV-vis spectroscopy. The mechanism of cleavage of the N-confused pyrrolic ring was investigated by theoretical calculations. The successful synthesis of other Pynes indicated the generality of this protocol.

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.

Fluoride ion Coordination-Induced Turn-On Fluorescence of Tailored N-Methyl N-Confused Tripyrromonomethene Analogues

Inorder to achieve striking compromise between flexibility and rigidity, two unprecedented highly air-stable N-methyl N-Confused tripyrromonomethene analogues in near quantitative yields have been synthesized by chloranil oxidation under aerobic condition....

Chemical transformation of Doubly N-Confused Porphodimethene to variants of (anti)Aromatic Doubly N-Confused Porphyrinoids and σ aromatic Doubly N-Confused Isophlorinoid

Chemical conversion of non-aromatic trans-doubly N-confused porphodimethene to hitherto unknown variants of doubly N-confused porphyrinoids/isophlorinoid have been unravelled by precise interplay between the types of oxidants, the types of meso-aryl...

Controlled assembly of a bicyclic porphyrinoid and its 3-dimensional boron difluoride arrays

A fully conjugated cryptand-like bicyclic porphyrinoid ligand 4, incorporating three carbazole linkages and four dipyrrin moieties, was prepared via the acid-catalysed condensation of an extended 2,2′-bipyrrole analogue containing a central carbazole moiety and 3,4-diethyl-2,5-diformylpyrrole in 79% isolated yield. This new cryptand-like system acts as an effective ligand and allows for complexation of BF₂ (boron difluoride) subunits. Three BODIPY arrays, containing two, three, and four BF₂ subunits, namely 4·2BF₂, 4·3BF₂ and 4·4BF₂, could thus be isolated from the reaction of 4 with BF₃·Et₂O in the presence of triethylamine at 110 °C, albeit in relatively low yield. As prepared, bicycle 4 is characterized by a rigid C₂ symmetric structure as inferred from VT NMR spectroscopic analyses. In contrast, the three BODIPY-like arrays produced as the result of BF₂ complexation are conformationally flexible and unsymmetric in nature as deduced from similar analyses. All four products, namely 4, 4·2BF₂, 4·3BF₂ and 4·4BF₂, were characterized by means of single crystal X-ray diffraction analyses. Tetramer 4·4BF₂ gives rise to a higher extinction coefficient (by 2.5 times) relative to the bis- and tris-BODIPY arrays 4·2BF₂ and 4·3BF₂. This was taken as evidence for stronger excitonic coupling in the case of 4·4BF₂. All three BODIPY-like arrays proved nearly non-fluorescent, as expected given their conformationally mobile nature. The efficiency of reactive oxygen species (ROS) generation was also determined for the new BODIPY arrays of this study.

A cryptand-like bicyclic porphyrinoid was obtained in preference over the monocyclic porphyrinoid by controlling the reaction stoichiometry and condensation conditions. The cryptand-like species supports formation of multiple 3D BODIPY-like arrays.

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.

Tetrabromo[36]octaphyrin: A Promising Precursor of Directly Fused Porphyrin(2.1.1.1) Dimer and meso-α Fused N-Confused Porphyrin Dimer

3,7,23,27-Tetrabromo[36]octaphyrin 2 was synthesized as a novel octaphyrin bearing two meso-free positions. Surprisingly, its Zn^II and Ni^II complexation reactions produced a directly fused porphyrin(2.1.1.1) dimer 6, and a meso-α fused N-confused porphyrin (NCP) dimer 7, as the first example of NCP tape, respectively, via transannular C-C bond formation. While 6 exhibits a diatropic ring-current effect owing to the global 36π Möbius aromaticity, 7 shows a paratropic ring-current effect due to the global Hückel 36π antiaromaticity. In addition, the oxidation of 7 with PbO₂ allowed for formation of its two-electron oxidized species 9 that exhibited a diatropic ring-current effect due to the global Hückel 34π aromaticity. This work has demonstrated that meso-free large expanded porphyrins can be a promising platform to produce novel fused porphyrinoids.

Synthesis and electrochemistry of nickel(II)porphyrins bearing external palladium(II) or platinum(II) complexes

The syntheses of nickel(II)porphyrins bearing palladium(II) or platinum(II) complexes at their periphery were performed. These new compounds were characterized by standard spectroscopic techniques and studied by electrochemistry. The electrochemical data were then compared with previously published data of porphyrin dimers linked by metal ions like palladium(II) or platinum(II). An X-ray structure of one of these species was obtained and confirmed the structure of this series of compounds.

Influence of solvent and axial coordination on self-assembly of a heteroditopic porphyrin derivative

A novel heteroditopic porphyrin and its zinc complex with four long aliphatic chains on the same side of the porphyrin ring were synthesized and used for controllable self-assembly. A variety of aggregation morphologies, including nanosheets, nanospheres, films, leaves, trunks, nanorods, and disks, were furnished by using different pyridyl ligands to coordinate with the Zn-porphyrin or selecting different solvents.

Structural isolation of NIR absorbing ferrocenyl bridged N-confused fused expanded phlorin, N-confused porphodimethene and the π-extended corrorin isomer: synthesis and characterization

Concise syntheses and spectroscopic, solid state X-ray crystal structure and theoretical studies of three electronically appealing new generation hitherto unknown ferrocenyl bridged N-confused heterocyclic macrocycles with (without) fusion are reported. Intriguingly, the expanded N-confused fused phlorin (1.1.1.1.1) with the built-in tripentacyclic [5.5.5] moiety exhibits tailing of the NIR absorption band beyond 1000 nm while the nonconjugated porphodimethene and a new generation π-extended isomeric corrorin analogue exhibit UV-vis absorption.

Tetracationic porphyrin derivatives against human breast cancer

Photodynamic therapy (PDT) is an approved therapeutic approach and an alternative to conventional chemotherapy for the treatment of several types of cancer with the advantages of reducing the side effects and developing resistance mechanisms. Here, was evaluated the photosensitization capabilities of 5,10,15,20-tetrakis[4-(pyridinium-1-yl-methyl)phenyl]porphyrin (3), its N-confused isomer (4) and of the neutral precursors (1) and (2) and the results were compared with the ones obtained with the cationic 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP). Both regular porphyrin derivatives 1 and 3 showed higher efficiency to generate singlet oxygen than TMPyP. The PDT assays towards MCF-7 cells under red light irradiation (λ > 640 nm, 23.7 mW cm^-2) demonstrated that the cationic porphyrin 3 is an efficient photosensitizer to kill MCF-7 breast cancer cells. The study of the cell death mechanisms induced by the photodynamic process showed that the studied porphyrin 3 and TMPyP caused cell death by autophagic flux and necrosis.

Perimeter Coordinated Diastereomeric Rh(I) Complex of Helically Twisted Weakly Aromatic Hybrid Singly N-Confused β-β Fused Ferrocenoporphyrinoids

Expedient synthesis, spectroscopic, solid state structural proof, and theoretical study of helically twisted weakly aromatic hybrid singly N-confused ferrocenoporphyrinoids and the peripheral coordinated Rh(I) complex are reported. The X-ray crystal structure of the macrocycles reveals an ambiguously inverted pyrrole ring reinforcing regioselective β,β-linkage with the spatially adjacent N-confused N-methyl pyrrole ring leading to endocyclic extension of macrocyclic π-conjugation via tricyclic [5.5.5] moiety. The three-dimensional structure with built-in fused tricyclic [5.5.5] moiety has paved way to three-dimensional weak diatropicity with vis-NIR absorptions. The peripheral coordinated Rh(I) complex owing to helical chirality about the macrocyclic ring and planar chirality about the square planar Rh coordination site exists as a mixture of diastereomers (5:3) with well resolved ¹H NMR spectra anticipating weak aromaticity. The experimental spectroscopic measurements are in agreement with theoretically determined electronic structure and properties strongly elucidating sustained weak diatropic ring currents in twisted macrocycles both in neutral form and in the metalated complex. Further fragment molecular orbital approach and molecular orbital theory gave insights on the stability of N-confused β-β fused oxo-ferrocenoporphyrinoids and formation of the selective peripheral coordinated Rh(I) complex.

Iridium Complex of N-Fused Bilatrienone: Oxidative Cleavage of N-Fused Porphyrin Induced by Iridium-Cyclooctadiene Complexation

N-fused porphyrin (NFP) is a unique class of photostable near-infrared dyes with an 18π aromatic tetrapyrrole macrocyclic skeleton containing a tri-fused pentacyclic moiety. Here, the synthesis of an iridium complex of N-fused bilatrienone is reported as the degradation product of Ir-cyclooctadiene (cod)-induced oxidative cleavage of NFP under aerobic conditions. Similar to the native bilin chromophores, the ring-opened complex featured a broken π-conjugation circuit and exhibited a broad visible absorption band. In contrast, metalation of NFP using an iridium(I)(cod) complex under an inert atmosphere resulted in the formation of a cod-isomerized (κ¹ ,η³ -C₈ H₁₂ )-Ir complex.

Neo-Porphyrinoids: New Members of the Porphyrinoid Family

The four pyrrole rings and four meso carbons of tetrapyrrolic porphyrins can be arranged in different ways and the resulting porphyrin isomers exhibit very distinct electronic properties. The extensive research carried out on the porphyrins over the years has revealed that porphyrin can have several possible isomers and some of these have been identified and synthesized. Among the porphyrin isomers synthesized so far, porphycene and N-confused porphyrins have been investigated extensively whereas the other porphyrin isomers such as hemiporphycene, corrphycene and isoporphycene remain underdeveloped because of synthetic difficulties and their inherently unstable nature. Neoporphyrinoids are new members of the porphyrinoid family that were discovered serendipitously in 2011. Neoporphyrinoids are structural analogues of porphyrinoids with a confused pyrrole nitrogen linked to a meso carbon or the adjacent pyrrole carbon. Thus, neoporphyrinoids have an unusual structure in which pyrrole N is a part of a porphyrinoid framework and the lone pair of electrons on nitrogen participate in macrocyclic conjugation. It's been a decade since the discovery and different types of neoporphyrinoids, including regular, contracted and expanded neoporphyrinoids, have been synthesized by rational synthetic methodologies and their spectral, structural, aromatic and coordination properties have been studied. There is huge scope to develop different synthetic routes to produce new types of stable neoporphyrinoids to study their properties and potential applications. This article presents a brief overview of the synthesis, structure and properties of the neoporphyrinoids reported in this decade.

Synthesis and Properties of Dibenzothiophene Embedded Heteroporphyrins

A series of new stable dibenzothiophene embedded heteroporphyrins were synthesized in 6-7% yields by condensing 1 equiv of dibenzothiophene-based tripyrrane with 1 equiv of four different diols, 2,5-bis(hydroxymethyl)heterocycles (furan, thiophene, selenophene, and tellurophene), under mild acid-catalyzed conditions in CH₂Cl₂. The formation of dibenzothiophene embedded heteroporphyrins was confirmed by high-resolution mass spectrometry and thoroughly characterized by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, absorption, electrochemical, and density functional theory/time-dependent density functional theory (DFT/TD-DFT) studies. The NMR studies indicated that the macrocycles were nonaromatic in nature. The electronic properties of the macrocycles were significantly altered as the heterocycle of the macrocycles was varied from furan to thiophene, selenophene, and tellurophene, as reflected clearly in the spectral and electrochemical properties. The macrocycles exhibited a sharp band in the region of 420-440 nm and a relatively broad absorption band(s) in the higher wavelength region of 550-800 nm. The oxa analogue was considerably blue-shifted as compared to the other macrocycles, whereas the tellura analogue exhibited relatively broadened and red-shifted absorption bands. Upon protonation of these macrocycles, the resulting diprotonated species displayed bathochromically shifted absorption bands, which were extended to the NIR region. DFT studies revealed that the macrocycles were highly distorted and strained and exhibited half chair conformation with restricted π-conjugation and confirmed their nonaromatic nature due to the lack of planarity of the macrocycle. TD-DFT studies were in agreement with the experimental spectral and electrochemical results.

Metal complexes of 5,10,15-tris(pentafluorophenyl)-20-pyrrolyl N-confused porphyrin and its meso-pyrrolyl-bridged dimers: Synthesis and optical properties

Inner- and peripheral-metal complexation behaviors of 5,10,15-tris(pentafluorophenyl)-20-pyrrolyl N-confused porphyrin (5) and its meso-pyrrolyl-bridged dimers (6-Ni and 7-Ni) were studied in this work. The resulting inner-Ag and peripheral-BF2 complex (5-AgBF[Formula: see text] exhibited the bathochromically shifted absorption feature ([Formula: see text]772 nm), which was attributed to the BF2 complexation. Furthermore, the bis-Ag/Ni complexes of dimer (6-Ag[Formula: see text]Ni and 7-Ag[Formula: see text]Ni) revealed remarkably lower energy bands in the deeper near-infrared ([Formula: see text] NIR-II) region ([Formula: see text] = 1226 and 1042 nm, respectively) through strong interchromophore interactions.

Doubly fused fluorene embedded heterosapphyrins

Synthesis and studies of first examples of nonaromatic doubly fused fluorene embedded heterosapphyrins and their intermediate macrocycles, monofused fluorene embedded hetero calixsapphyrins are reported.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting

The recent advances in the field of two-photon absorbing chromophores in the short-wavelength infrared spectral range (SWIR 1100–2500 nm) are summarized, highlighting the development of optical power limiting devices in this spectral range.

Ruthenium(iv) N-confused porphyrin μ-oxo-bridged dimers: acid-responsive molecular rotors

Ruthenium(iv) N-confused porphyrin μ-oxo-bridged complexes were synthesized via oxidative dimerization of a ruthenium(ii) N-confused porphyrin complex using 2,2,6,6-tetramethylpiperidine 1-oxyl. The deformed core planes in the dimers conferred a relatively high ring rotational barrier of ca. 16 kcal mol⁻¹. Rotation of the complexes was controlled by protonating the peripheral nitrogen.

Ring rotation of ruthenium(iv) N-confused porphyrin μ-oxo-dimer was controlled by protonation at the peripheral nitrogen moieties.

Pyrrole-Modified Porphyrins Containing Eight-Membered Heterocycles Using a Reversal of the "Breaking and Mending" Strategy

The conversion of meso-aryl-porphyrins/chlorins to porphyrinoids containing nonpyrrolic heterocycles (so-called pyrrole-modified porphyrins, PMPs) along an approach we dubbed "the breaking and mending of porphyrins" is well known. However, examples are limited to the synthesis of PMPs containing up to six-membered heterocycles; the syntheses of larger rings failed. We report here hitherto unavailable eight-membered chlorin-type PMPs using an inverted "mending and breaking" approach. All examples are based on the addition of N,N'-dimethylurea derivatives to a meso-phenyl-β,β'-dioxoporphyrin, followed by oxidative cleavage of the intermediate diol adduct. We correlate the extremely nonplanar solid-state structures of three crystallographically characterized PMPs containing an eight-membered ring with their solution-state optical properties. The first examples of bis-modified, bacteriochlorin-type PMPs containing either two eight-membered rings or an eight-membered ring and an imidazolone ring are also detailed. Using other N,N'-nucleophiles failed to either generate chlorins containing a β,β'-dihydroxypyrroline, a prerequisite for the "breaking step," or the cleavage of those substrates that did generate a diol underwent subsequent reactions that thwarted the generation of the desired PMPs. This contribution adds novel PMPs containing eight-membered rings, highlights the effects these derivatizations have on the macrocycle conformation, and how that affects their optical properties.

Porphyrinoids with Vinylene Bridges

Porphyrinoids containing vinylene bridges, such as triphyrin(2.1.1), porphycene, porphyrin(2.1.2.1), and hexaphyrin(2.1.2.1.2.1), are a relatively new family of porphyrinoids. Vinylene bridges give porphyrinoids a lower symmetry and a flexibility of the framework and they permit cis/trans-isomerization reactions; these factors confer unique properties to these substances, such as coordination to metal ions and aromaticity switching. In this account, the synthesis, crystal structures, and properties of new porphyrinoids containing vinylene bridges are summarized.

1 Introduction

2 Triphyrin(2.1.1)

3 Porphycene

4 Porphyrin(2.1.2.1)

5 Hexaphyrin(2.1.2.1.2.1)

6 Conclusion

Synthesis and Structure of meso-Substituted Dibenzihomoporphyrins

Bench-stable meso-substituted di(p/m-benzi)homoporphyrins were synthesized through acid-catalyzed condensation of dipyrrole derivatives with aryl aldehydes. The insertion of a 1,1,2,2-tetraphenylethene (TPE) or but-2-ene-2,3-diyldibenzene unit in the porphyrin framework results in the formation of dibenzihomoporphyrins, merging the features of hydrocarbons and porphyrins. Single crystal X-ray analyses established the non-planar structure of these molecules, with the phenylene rings out of the mean plane, as defined by the dipyrromethene moiety and the two meso-carbon atoms. Spectroscopic and structural investigations show that the macrocycles exhibit characteristics of both TPE or but-2-ene-2,3-diyldibenzene and dipyrromethene units indicating the non-aromatic characteristics of the compounds synthesized. Additionally, the dibenzihomoporphyrins were found to generate singlet oxygen, potentially allowing their use as photosensitizers.

Targeted synthesis of meso-aryl substituted aromatic trans-doubly N-confused dithia/diselena [18] porphyrins (1.1.1.1) with NIR absorption: spectroscopic and theoretical characterization

High yield synthesis and spectroscopic isolation of two hitherto unknown highly stable single conformers of meso-aryl substituted dithia/diselena trans-doubly N-confused porphyrins with fully π-conjugated [18] annulene structures are reported. In-depth solution state spectroscopic measurements and DFT level theoretical calculations strongly show the distinct aromaticity with strong NIR absorption of these new macrocycles.

N-Confused Porphyrin - A Unique "Turn-On" Chemosensor for CN- and F- ions and "Turn-Off" Sensor for ClO4 - ions

N-Confused meso-tetrakis(4-carbomethoxyphenyl)porphyrin (1) and its Ni(II) complex (1 a) have been synthesized and utilized for anion sensing studies, and the results are compared with N-confused meso-tetraphenylporphyrin (NCTPP). Anion susceptibilities of 1 and 1 a were investigated using spectroscopic, electrochemical, and DFT studies. Porphyrins 1 and 1 a were able to detect CN^- , F^- , and ClO₄ ^- ions selectively over the tested set of anions even at ppm level. Interestingly, the addition of ClO₄ ^- ions resulted in fluorescence quenching (turn off) whereas the addition of F^- or CN^- resulted in fluorescence enhancement (turn on). Notably, the TFA addition resulted in fluorescence quenching, whereas the fluorescence enhancement was observed while adding TBAOH. The higher association constant (K_a ) values with anions, lower detection limit, and shifts in redox potentials are due to the electron-withdrawing effect of the -COOCH₃ group at the para-position of the meso-phenyl ring. This electron-withdrawing nature is crucial for the higher affinity towards anions. The anion sensing description in this article may not only unveil the built-in nature of N-confused porphyrins, but may also provide a general proposal for the development of novel anion sensors based on porphyrinoids. The electron-deficient porphyrin framework, large polarisable π-system, and anion binding through the outer NH or a combination of the above factors serve as a foundation for N-confused porphyrin to act as an anion sensor.

Rational Synthesis of 5,5,5-Tricyclic Fused Thia-heptaphyrin (1.1.1.1.1.1.0) From a Helical Oligopyrrin Hybrid

Oxidation of a thiophene-hexapyrrane hybrid S-P₆ afforded a stable conjugated open-chain thiaheptapyrrolic helix 1 with the terminal thiophene and confused pyrrole units lying at a long distance that is adverse for further cyclization. Chelation of 1 with copper(II) ion afforded 1-Cu, which exhibits more distant terminal units. Interestingly, further oxidation of 1 triggered an intramolecular C-N fusion reaction to afford a unique 5,5,5-tricyclic fused linear thiaheptapyrrin 2, with the two terminals positioned in proximity, which favors the oxidative ring-closure reaction to give a unique 5,5,5-tricyclic fused thiaheptaphyrin (1.1.1.1.1.1.0) 3 under air. The inner-fusion strategy for positioning the reactive sites in proximity to promote oxidative cyclization offers a new approach for constructing large porphyrinoids through conjugated oligopyrrins without the assistance of metal ions.

Comparative in vitro Studies of the Topoisomerase I Inhibition and Anticancer Activities of Metallated N-Confused Porphyrins and Metallated Porphyrins

Using the original approach, a series of metallated N-confused porphyrins and metallated porphyrins have been synthesized and characterized. For all the synthesized porphyrins, in vitro studies of cytotoxic activity against K562, U937, HL-60, Jurkat, A549 and HeLa cancer cell lines, the ability to induce apoptosis and effects on the cell cycle as well as the kinetics of proliferative activity of porphyrins and their respective metallated complexes in real time have been developed. The inhibitory activity of metallated porphyrins against human topoisomerase I and the possible mechanism of inhibition have been carried out by modelling using molecular docking.

Synthesis of 2-bromo- and 2-phenyl-neo-confused porphyrins

New examples of neo-confused porphyrins are reported. These retain global diatropic characteristics but are relatively unstable in solution.

Unexpected Rearrangement of Dilithiated Isoindoline-1,3-diols into 3-Aminoindan-1-ones via N-Lithioaminoarylcarbenes: A Combined Synthetic and Computational Study

The reaction of 2-aryl-3-hydroxyisoindolin-1-ones with the s-BuLi·TMEDA system in THF at -78 °C, affording a series of diastereomeric 3-aminoindan-1-ones via a novel rearrangement of the isoindolinone scaffold, is reported. It is proposed that α-elimination of LiOH from the transient N,O-dilithiated hemiaminal carbenoids leads to the formation of singlet carbenes followed by their trapping via an intramolecular C-H insertion. An alternative explanation based on an intramolecular Mannich reaction seem much less probable. A mechanistic-type study that combines spectroscopic data of the products and calculation results, with a special focus on the diverse lithiated intermediates that are most likely to engage in the title process (particularly those with internal Li bonds), is presented. The MP2 approach, including the NPA and QTAIM data, provided insight into structures and properties of all these species. Two reaction routes A and B appeared to be possible for the postulated carbene mechanism. An unusual metamorphosis of the CCN atom triad, from a near sp 1-azaallene-type in more stable noncarbene Li enolates to a roughly sp² type in their carbene keto tautomers, is recognized in one of these pathways (route B). Dominant forms of resonance structures for the aforementioned tautomeric systems that have seven-membered quasi rings stabilized by Li⁺ ions bridging the N and carbonyl O atoms are indicated. Large computational difficulties arising from a huge impact of internal Li⁺ complexation on conformational preferences and electronic properties of carbonyl group-bearing lithium derivatives are also discussed. The new γ-keto carbene species under study belong to a subclass of acyclic aminoarylcarbenes.

UO2 2+-mediated ring contraction of pyrihexaphyrin: synthesis of a contracted expanded porphyrin-uranyl complex

A new mixed hexaphyrin, pyrihexaphyrin (0.1.0.0.1.0) (1), was prepared via an acid catalyzed cyclization between 5,5′-(pyridine-2,6-diyl)bis(pyrrole-2-carbaldehyde) (2) and terpyrrole (3).

A new mixed hexaphyrin, pyrihexaphyrin (0.1.0.0.1.0) (1), was prepared via an acid catalyzed cyclization between 5,5′-(pyridine-2,6-diyl)bis(pyrrole-2-carbaldehyde) (2) and terpyrrole (3). This expanded porphyrin undergoes a ring contraction upon metallation with uranyl silylamide [UO₂[N(SiMe₃)₂]₂] under anaerobic conditions followed by purification over basic aluminum oxide exposed to air. The uranyl-contracted pyrihexaphyrin (0.0.0.0.1.0) complex (4) produced as a result contains a unique structural architecture and possesses a formally 22 π-electron globally aromatic periphery, as inferred from NMR spectroscopy, single crystal X-ray diffraction, and computational analyses. Support for the proposed contraction mechanism came from experimental data and DFT calculations. Proton NMR and mass spectroscopic analysis provided the first insight into expanded porphyrin-mediated activation of the uranyl dication (UO₂²⁺).