SnIV Complexes of N-Confused Porphyrins and Oxoporphyrins—Unique Fluorescence “Switch-On” Halide Receptors

2,5-Thienylene-Strapped [26]Hexaphyrin as Multifunctional Chemosensor for Hg2+, Cu2+, and F- Ions

The sensing behavior of 2,5-thienylene-bridged tetrakis(2,6-dichlorophenyl)-[26]hexaphyrin (2) towards various metal ions and anions were investigated by UV-vis and fluorescence spectroscopies. Using this strapped hexaphyrin (2), the molecular sensor displayed highly selective and sensitive colorimetric responses to Cu2+ and Hg2+ in MeOH/THF. The spectral changes are distinctive enough in the visible region of the spectrum to enable naked-eye detection. The detection limits of Cu2+ and Hg2+ using this chemo-sensor in a mixed MeOH/THF solution were 1.978 and 1.283 μM, respectively, and 1.052 μM for F- in dichloromethane. Chemosensor 2,5-thienylene strapped [26]hexaphyrin (2) shows absorption responses both a 1 : 1 molecular ratio for 2 interacting with Cu2+ and Hg2+ and a 1 : 2 ratio between 2 and F- ions.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

Complexes of N-Confused Porphyrin Derivatives as Ortho-Metallating Ligands. Synthesis, Structure, Redox Properties, and Chirality

A family of transition metal complexes of meso-aryl-2-aza-21-carbaporphyrin (N-confused porphyrin, NCP) derivatives acting as ortho-metallating ligands for ruthenium(II), rhodium(III), and iridium(III) is synthesized and characterized by XRD, spectroscopic, and electrochemical methods. The chirality of these systems is shown by the separation of the enantiomers and analyzed by circular dichroism and DFT. A preliminary catalytic study indicates the activity of the iridium(III) ortho-metallated complexes in the N-heterocyclization of primary amines with diols.

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.

Synthesis and Properties of Stable 20π Porphyrinoids

The 20π porphyrinoids are immediate higher homologues of 18π porphyrins and differ from porphyrins in aromaticity which in turn affects the structure, properties and chemical reactivities. Research over the years indicated that the 20π porphyrinoids can be stabilized as non-aromatic/anti-aromatic or Mobius aromatic macrocycles using different strategies such as core-modification of porphyrins, non-metal/metal complexation of porphyrins, peripheral modification of porphyrins and expanded porphyrinoids. The structural properties such as aromaticity of the macrocycle can be controlled by choosing the right synthetic strategy. This review will provide an overview of the development in the chemistry of 20π porphyrinoids giving emphasize on the synthesis, structure and electronic properties of these macrocycles which have huge potential for various applications.

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.

Sn(IV) N-confused porphyrins as photosensitizer dyes for photodynamic therapy in the near IR region

The utility of Sn(iv) N-confused porphyrin (SnNCP) for use as photosensitizer dyes in photodynamic therapy is investigated. SnNCP has an unusually high singlet oxygen quantum yield of 0.72 in DMSO. IC50 values of 1.6 and 12.8 μM were obtained against MCF-7 cells upon irradiation with 660 and 780 nm LEDs.

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.

Reactions of 2-aza-21-carbaporphyrin with aniline derivatives

Post-synthetic modification of N-confused porphyrin (NCP) yields chiral 21-arylazo- or 3,21-bis(arylamino)-NCP in one-step, one-pot reactions of NCP with anilines.

aza-BODIPY synthesis towards vis/NIR functional chromophores based on a Schiff base forming reaction protocol using lactams and heteroaromatic amines

The Schiff base forming reaction of lactams and heteroaromatic amines led to creation of a new class of aza-BODIPY analogues as visible and near infrared functional chromophores.

DNA-binding, photocleavage and anti-cancer activity of tin(IV) corrole

A new tin(IV) corrole, 5,10,15-tris(4-methoxycarbonylphenyl) corrole tin(IV) (1-Sn) was synthesized and characterized. The DNA binding, photocleavage and anti-cancer activity were studied and compared with its free-base. The interaction of 1-Sn and its free-base 1 with calf thymus DNA had been investigated by spectroscopic methods, viscosity measurements and molecular docking analysis. The results revealed that 1-Sn and 1 could interact with calf thymus DNA via an outside groove binding mode. Furthermore, although 1 displayed no photonuclease activity, 1-Sn exhibited good photonuclease activity as indicated by agarose gel electrophoresis, and superoxide anion might be the active intermediate for the DNA scission. Finally, 1 was nontoxic but 1-Sn displayed cytotoxicity towards A549 tumor cell lines.

N-Confused Porphyrin Immobilized on Solid Supports: Synthesis and Metal Ions Sensing Efficacy

In this work, the N-confused porphyrin 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrin (NCTPP) was immobilized on neutral or cationic supports based on silica and on Merrifield resin. The new materials were characterized by appropriate techniques (UV-Vis spectroscopy, SEM, and zeta potential analysis). Piezoelectric quartz crystal gold electrodes were coated with the different hybrids and their ability to interact with heavy metals was evaluated. The preliminary results obtained showed that the new materials can be explored for metal cations detection and the modification of the material surface is a key factor in tuning the metal selectivity.

Synthesis of 3-cyano-N-confused porphyrin derivatives by silyl cyanide

3-Cyano- N-confused porphyrin derivatives were synthesised by the reaction of N-confused porphyrin with trimethylsilyl cyanide in the presence of tetrabutylammonium fluoride in moderate yield. The reaction took placed regioselectively in the 3-position carbon of the inverted pyrrole of N-confused porphyrins.

Highly electron deficient tetrabenzoquinone-appended Ni(ii) and Cu(ii) porphyrins: spectral, solvatochromatic, electrochemical redox and tuneable F−and CN−sensing properties

The electron deficient tetrabenzoquinone-appended porphyrins (1and2) were synthesized and utilized for the selective detection of CN⁻ions in aqueous media whereas they detect F⁻and CN⁻ions in nonaqueous media.

Development of Ion Chemosensors Based on Porphyrin Analogues

Sensing of metal ions and anions is of great importance because of their widespread distribution in environmental systems and biological processes. Colorimetric and fluorescent chemosensors based on organic molecular species have been demonstrated to be effective for the detection of various ions and possess the significant advantages of low cost, high sensitivity, and convenient implementation. Of the available classes of organic molecules, porphyrin analogues possess inherently many advantageous features, making them suitable for the design of ion chemosensors, with the targeted sensing behavior achieved and easily modulated based on their following characteristics: (1) NH moieties properly disposed for binding of anions through cooperative hydrogen-bonding interactions; (2) multiple pyrrolic N atoms or other heteroatoms for selectively chelating metal ions; (3) variability of macrocycle size and peripheral substitution for modulation of ion selectivity and sensitivity; and (4) tunable near-infrared emission and good biocompatibility. In this Review, design strategies, sensing mechanisms, and sensing performance of ion chemosensors based on porphyrin analogues are described by use of extensive examples. Ion chemosensors based on normal porphyrins and linear oligopyrroles are also briefly described. This Review provides valuable information for researchers of related areas and thus may inspire the development of more practical and effective approaches for designing high-performance ion chemosensors based on porphyrin analogues and other relevant compounds.

[28]Hexaphyrin derivatives for anion recognition in organic and aqueous media

Hexaphyrin-based anion chemosensors are reported for the first time.

Switching between porphyrin, porphodimethene and porphyrinogen using cyanide and fluoride ions mimicking volatile molecular memory and the ‘NOR’ logic gate

β-Substituted porphyrins were developed as a quantitatively operating “lab-on-a-molecule” for the detection of F⁻and CN⁻ions, by switching between porphyrin, porphodimethene and porphyrinogen along with distinct solution colour changes and reversibility.

Near-infrared luminescent Sn(IV) complexes of N-confused tetraphenylporphyrin: Effect of axial anion coordination

Novel tin(IV) halo complexes of an N-confused tetraphenylporphyrin with different axial ligands have been synthesized and characterized by various spectroscopic methods including X-ray crystallographic analysis. The molecular structures of the dichloro and dibromo derivatives possess perfect octahedral geometries, which are nearly comparable to the corresponding regular porphyrin complexes. In contrast, the iodide/triiodide complex obtained by a same reaction manner, demonstrated that the tin(IV) cation is slightly displaced towards axially coordinated iodide anion, giving rise to the different electronic structure due to the tautomeric form of N-confused porphyrin ligand. These structural differences reflected to the distinct photophysical and electrochemical properties. The Sn(IV) complexes are near IR luminescent, however the unsymmetrical axial coordination of iodide and triiodide anions in the tin(IV) N-confused porphyrin complex allows, in particular, the longer emission lifetimes and a smaller singlet-triplet energy gap, which were investigated by steady-state and time-resolved spectroscopies as well as theoretical calculations.

Fluorescent and colorimetric ion probes based on conjugated oligopyrroles

In this tutorial review, the design strategies, syntheses, and ion sensing properties of conjugated oligopyrroles are described.

Colorimetric “naked eye” detection of CN−, F−, CH3COO−and H2PO4−ions by highly nonplanar electron deficient perhaloporphyrins

Highly nonplanar electron deficient perhaloporphyrins were utilized for the detection of basic anions such as CN⁻, F⁻, CH₃COO⁻and H₂PO₄⁻viaanion induced deprotonation. These sensors can be reusable without loss of their sensing ability.

L-Proline catalyzed reaction of N-confused porphyrin and active methylene compounds

Active methylene compounds such as acetone, butanone, cyclopentanone, nitromethane, malononitrile, ethyl 2-cyanoacetate, diethyl malonate, and ethyl acetylacetate react with the C3 position of N-confused porphyrin in the presence of L-proline in refluxing THF-EtOH affording a variety of N-confused porphyrin derivatives in moderate yield. L-Proline catalyzes the reaction facilitating the formation of the carbanion derived from an active methylene compound simultaneously delivering protons to the N-confused porphyrin. Both processes are key factors of this reaction.

Porphyrin-based sensor nanoarchitectonics in diverse physical detection modes

Porphyrins and related families of molecules are important organic modules as has been reflected in the award of the Nobel Prizes in Chemistry in 1915, 1930, 1961, 1962, 1965, and 1988 for work on porphyrin-related biological functionalities. The porphyrin core can be synthetically modified by introduction of various functional groups and other elements, allowing creation of numerous types of porphyrin derivatives. This feature makes porphyrins extremely useful molecules especially in combination with their other interesting photonic, electronic and magnetic properties, which in turn is reflected in their diverse signal input-output functionalities based on interactions with other molecules and external stimuli. Therefore, porphyrins and related macrocycles play a preeminent role in sensing applications involving chromophores. In this review, we discuss recent developments in porphyrin-based sensing applications in conjunction with the new advanced concept of nanoarchitectonics, which creates functional nanostructures based on a profound understanding of mutual interactions between the individual nanostructures and their arbitrary arrangements. Following a brief explanation of the basics of porphyrin chemistry and physics, recent examples in the corresponding fields are discussed according to a classification based on physical modes of detection including optical detection (absorption/photoluminescence spectroscopy and energy and electron transfer processes), other spectral modes (circular dichroism, plasmon and nuclear magnetic resonance), electronic and electrochemical modes, and other sensing modes.

PEGylated meso-arylporpholactone metal complexes as optical cyanide sensors in water

A number of water-soluble metal complexes of PEGylatedmeso-fluorophenylporpholactones display a specific optical response upon addition of cyanide.

Neutral CH and cationic CH donor groups as anion receptors

Neutral and cationic CH hydrogen bond donors have been actively used in various shape persistent macrocycles, foldamers and “molecular machines”.

α-Monoacylated and α,α'- and α,β'-diacylated dipyrrins as highly sensitive fluorescence "turn-on" Zn2+ probes

With the purpose of developing readily synthesized CHEF (chelation-enhanced fluorescence) type Zn(2+) probes with relatively simple molecular structures and excellent sensing behavior, p-anisoyl chloride was used for the acylation of 5-(pentafluorophenyl)dipyrromethane. Interestingly, the α,β'-diacylated product PS2 with a unique substitution mode was obtained in high yield in addition to the normal α-substituted mono- and diacylated products PS1 and PS3. Further oxidation of PS1-PS3 afforded dipyrrins S1-S3. Crystal structure and (1)H NMR measurements of S2 demonstrate the existence of a pure tautomer, which is consistent with DFT calculations. S1-S3 show highly Zn(2+) selective "turn-on" fluorescence based on a CHEF mechanism by the formation of 2:1 (probe:metal) Zn(2+) complexes. The emission colors can be easily tuned from green to red by changing the dipyrrin substitution modes. Furthermore, these probes demonstrate fast responses and wide applicable pH ranges. Among them, S2 shows the highest Zn(2+) sensitivity, with a detection limit of 4.4 × 10(-8) M.