Journal of Porphyrins and Phthalocyanines

In the synthesis of cobyric acid following an arduous 60-step synthesis of the tetrapyrrole corrigenolide, Woodward demonstrated that ring cyclization yielded unexpectedly the corrin cyclic ether (Fig. 2). Its structure was chosen as the chemistry logo for the 1970 IUPAC meeting. It was a reminder that chemistry can be capricious and beautiful. This article is a tribute to the 50-year career in porphyrins of Professor Kevin M. Smith and describes his early contributions with colleagues in the synthetic quest of a related porphyrin molecule, vitamin B₁₂ (Fig. 1a).

Porphyrins and their structural analogs have drawn continuous attention owing to their physico-chemical properties associated with biological, medical and material chemistry. Consequently, many structural modifications of the porphyrin skeleton have been reported as a fundamental tool for tuning the physico-chemical properties and a variety of new classes of porphyrinoids have emerged. A vast number of applications such as photodynamic therapy (PDT), redox catalysis, chemosensors, nonlinear optical material (NLO) and two photon absorption (TPA) have been studied utilizing these systems. The “so called” meso-alkylidenyl porphyrins have been reported recently as alternative modification methods of the porphyrin skeleton. These compounds possess one or more exocyclic double bonds at meso-positions and are usually non-aromatic systems. The reported spectroscopic as well as structural properties well-corroborate the non-aromatic nature of the macrocycles. However, the protonation behavior and tautomerism are quite different from those of normal porphyrins. Considering the unique properties of meso-alkylidenyl carbaporphyrinoid macrocycles, we present a review on the recent advances in this area of chemistry.

In this manuscript, we have overviewed thermal and photoinduced electron transfer catalysis of high-valent metal-oxo porphyrins in oxidation of various substrates. The high-valent iron-oxo porphyrin in cytochrome P450 (P450) is produced by photoinduced electron transfer from electron donors, such as triethanolamine (TEOA), to the excited state of a photosensitizer such as eosin Y, followed by the reduction of the heme domain of P450 by the resulting radical anion of the photosensitizer and the subsequent reaction of the reduced heme with dioxygen (O${}_2)$. Various substrates were oxidized by O₂ in this visible light-driven electron-transfer catalytic reaction with several P450s from bacteria and humans. A manganese(V)-oxo corrorazine was produced by photoinduced electron transfer from the excited state of manganese(III) corrorazine to O₂, followed by hydrogen abstraction from toluene derivatives, catalyzing the oxidation of toluene derivatives with O₂ in the presence of an acid via photoinduced electron transfer catalysis. High-valent manganese-oxo porphyrins are also produced by photoinduced electron transfer from the excited state of [Ru(bpy)₃]${}^{2+}$ (bpy = 2,2^′-bipyridine) to electron acceptors, followed by electron transfer oxidation of manganese(III) porphyrins with [Ru(bpy)₃]${}^{3+}$, catalyzing oxidation of various substrates with O₂. Finally photoinduced electron-transfer catalysis of cobalt porphyrins is discussed for the photocatalytic water oxidation with persulfate.

The easy access and low price of pyrrole and aldehydes, conjugated with the simplicity in preparing meso-substituted porphyrins, makes this type of porphyrins very attractive for a broad range of applications. However, there is an increasing demand for the development of new synthetic processes involving more sustainable chemical principles substituting, whenever possible, dangerous organic solvents by alternative solvents, chromatographic purifications by precipitations and energy-intensive procedures by alternative energy sources such as microwaves and ultrasounds. In this review we will address some recent strategies to synthesize meso-substituted porphyrins using alternative energy sources, reaction media and catalysts, namely microwave irradiation, water as solvent, or solid microporous acid catalysts.

BODIPY and aza-BODIPY fluorophores linked to steroids are being developed as multimodal-imaging agents to monitor the mechanism of action of biologically active components in living systems.

Porphyrins are abundant in nature facilitating many enzymatic reactions by being present in the active sites of many enzymes. Consequently, over the years, a number of chiral metalloporphyrins have been synthesized and have proved efficient in catalyzing C–C bond forming reactions. Herein, we review the synthesis of chiral metalloporphyrins and their catalytic activity in cyclopropanation, cyclopropenation, and C–H insertion reactions.

This review highlights synthesis procedures to obtain A₃-, cis- and trans- A₂B- and ABC-corroles. Synthesis methods from the early beginning of “corrole chemistry”, acid-catalyzed condensation methods of various building blocks (pyrrole, aldehyde, dipyrromethane, dipyrromethane-carbinol, and dipyrromethane-dicarbinol etc.), possible side reaction during Brønsted acid catalyzed reactions (scrambling), one-pot synthesis of corroles, and post-macrocyclization modification reactions of meso-substituted A₃-corroles are discussed.

Coupled oxidation of iron tetraphenylporphyrins was studied as a tool for preparation of various linear tetrapyrroles. We obtained two linear tetrapyrrole products, biladienone with the meso carbon retained and bilindione with one of the meso carbons eliminated. Biladienone was isolated as a 15-hydroxy derivative. Acid catalyzed elimination of water from biladienone yielded bilatrienone. Bilindione was converted to the zinc complex of 5-oxaporphyrin by reacting it with acetic anhydride and zinc acetate. The zinc complex of 5-oxaporphyrin was a labile electrophile, and readily reacted with a weak nucleophile such as methanol or ethanol. The nucleophilic ring cleavage was used to prepare a variety of bilinone derivatives with substituent at the terminal pyrrole ring. The zinc complex of 5-oxaporphyrin fluoresced red light with a quantum yield of 7%. Free base bilinone showed solvatochromism by forming proton-transferred hydrogen bonding with aprotic amide, which bears similarity to the red to far-red photochromism of phytochromes. The zinc complex of biladienone bearing long alkyl chains was used as an active layer of molecular switch, where flexible framework of linear tetrapyrrole and self-assembling properties lead to 10³ fold electric current reduction by application of an external electric field. The zinc complex of biladienone showed allosteric binding to amines, where allosteric behavior was caused by its dimerization.

This minireview highlights the unusual coordination geometries observed in bimetallic complexes of mercury, thallium, lead and bismuth. These bimetallic complexes remain scarce and through an analysis of their X-ray structures, the various structural features that favorise them will be underlined.

If life without heme-Fe were at all possible, it would definitely be different. Indeed this complex and versatile iron-porphyrin macrocycle upon binding to different “globins” yields hemeproteins crucial to sustain a variety of vital functions, generally classified, for convenience, in a limited number of functional families. Over-and-above the array of functions briefly outlined below, the spectacular progress in molecular genetics seen over the last 30 years led to the discovery of many hitherto unknown novel hemeproteins in prokaryotes and eukaryotes. Here, we highlight a few basic aspects of the chemistry of the hemeprotein universe, in particular those that are relevant to the control of heme-Fe reactivity and specialization, as sculpted by a variety of interactions with the protein moiety.

New methods for water treatment are required as a result from an increasing awareness in the reduction of the pollution impact in the environment. In the perspective of the photo-oxidation of organic pollutants present in water, the principal incentive for the preparation of heterogeneous photocatalysts is their easy recovery from the reaction mixture, which allows their reuse in successive runs, minimizing the loss of their original photocatalytic properties. Different types of supports can be used in the immobilization of photoactive species, such as porphyrins (Pors) and phthalocyanines (Pcs). This mini-review will consider the different methodologies for the immobilization of Pors and Pcs and their photocatalytic performance in the photodegradation of organic pollutants in water, addressing also their recycling ability in successive water treatments.

This review focuses on synthetic strategies that have been established for the preparation of porphyrin-quinone conjugates of potential biological significance and as donor–acceptor compounds for electron transfer processes.

This review deals with the use of ruthenium porphyrin complexes to catalyze hydrocarbon aminations. This class of versatile porphyrin catalysts are able to activate different nitrogen sources, such as iminoiodinanes and organic azides, and promote the synthesis of a variety of aza-derivatives. Many synthetic procedures have been discussed as well as catalytic mechanisms involved in order to give an overview on the use of ruthenium porphyrins to promote nitrene transfer reactions yielding aminated derivatives.

Novel tetraphenylporphyrin-subphthalocyanine conjugates have been prepared and characterized. An analysis of their optical spectroscopy and electronic structures using fluorescence emission and magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations, demonstrates that the two chromophores do not interact to any significant extent.

Synthesis and isolation of selectively brominated tetraarylporphyrin derivatives is reported. Treatment with bromine of meso-5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrin (1) or meso-5,10,15,20-tetrakis(3,5-di-$t$-butyl-4-hydroxyphenyl)porphinatocopper(II) (2-Cu) yields products octabrominated at the 2,6-positions of meso-aryl substituents [5,10,15,20-tetrakis(2,6-dibromo-3,4,5-trimethoxyphenyl)porphyrin, ${}^{2,6}$Br₈1] or macrocyclic $\beta$-positions. The latter of these ($\beta$-brominated) was identified as the oxoporphyrinogen 2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(3,5-di-$t$-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen 3 obtained due to the adventitious oxidation and demetalation of 2-Cu, which could be alkylated at its macrocyclic nitrogen atoms yielding N${}_{21}$,N${}_{22}$,N${}_{23}$,N${}_{24}$-tetrakis(4-bromobenzyl)-2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(3,5-di-$t$-butyl-4-oxo-cyclo hexa-2,5-dienylidene)porphyrinogen 4. The former compound ${}^{2,6}$Br₈1 was complexed with Zn(II) (${}^{2,6}$Br₈1-Zn) or Cu(II) (${}^{2,6}$Br₈1-Cu) and could also be subjected to further bromination yielding 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2,6-dibromo-3,4,5-trimethoxyphenyl)porphyrin, Br${}_{16}$1. The effect on the electrochemical properties of the 2,6-bromophenyl-substituted porphyrin compounds over the more highly brominated products was assessed.

The novel polyfluorinated thioalkyl-porfirazine 2,3,7,8,12,13,17,18-octakis(1,1,1,2,2,-3,3,4,4-nonafluorohexylthio)-5,10,15,20-21H,23H-porfirazine was synthesized to investigate the fluorine effect on self-aggregation, electrochemical, and spectral properties of this class of tetrapyrrole macrocycles. This compound showed an ordered and quite thermally stable columnar discotic mesophase, never seen in non-fluorinated symmetrically substituted “free-base” thioalkyl-porphyrazines, revealing a significant effect of fluorine on molecular self-assembling properties. An important effect of fluorination was also observed on the spectral and electrochemical properties of the molecule, giving rise to a hypsochromic shift in the 400–700 nm range of UV-vis absorption spectrum and to a marked cathodic shift of the reduction potentials in respect to the non-fluorinated analogs. DFT and TDDFT calculations has been undertaken to elucidate the origin of the observed behavior. Interestingly, HOMO, LUMO, and band-gap values together with its mesomorphic properties make this compound a promising material for organic photovoltaics.

Mono and bis ethynyl and ethynylphenyl $\beta$-substituted porphyrins have been synthesized and characterized. Their conformational properties have been analyzed through a combination of NMR experiments and molecular mechanic calculations, while UV-Vis absorption and fluorescence measurements together with electrochemical studies allows us to probe the existence of intramolecular electronic processes. The role of the beta-substituents and of the spacer is underlined.

meso–meso Directly-linked trimeric and pentameric porphyrin–hexaphyrin hybrid arrays 5 and 6 comprising of electron-deficient porphyrin units were prepared by cross-condensation of monomeric and dimeric electron-deficient meso-formyl porphyrins with a tripyrrane. The solid-state structures of 5 and 6 have been determined by single crystal X-ray diffraction analysis. The latter is the largest crystal structure of meso–meso linked multiporphyrinic array analogues reported to date.

The reaction of [Fe(TMP)(OClO${}_3)$], where TMP is the dianion of tetramesitylporphyrin, with a combination of a strong $\pi$-acceptor ligand and a $\pi$-donating imidazole can lead to the preparation of mixed-ligand complexes [Fe(Porph)(4-CNPy)(L)]${}^{+}$ where L is imidazole itself or 1-acetylimidazole and 4-cyanopyridine is the strong $\pi$ acceptor ligand. The stability of the new mixed-ligand pair is the presumed result of synergic bonding between the two axial ligands. The molecular structure and other characterization of the new mixed axial ligand complex, [Fe(TMP)(4-CNPy)(HIm)]ClO₄ is described. The axial ligands have a relative perpendicular arrangement with Fe–N(imidazole) = 1.945 Å and Fe–N(pyridine) = 2.021 Å. The average equatorial Fe–N${}_{\mathrm{\text{p}}}$ distance is 1.963 Å, which is consistent with the S₄-ruffled TMP core. Despite the relative perpendicular arrangement of axial ligands, the EPR spectrum of the complex is a rhombic signal and not a large g_max signal. The EPR g-values are ${\mathrm{\text{g}}}_1=$ 3.05, ${\mathrm{\text{g}}}_2=$ 2.07, and ${\mathrm{\text{g}}}_3=$ 1.22. A quadrupole doublet was seen in the Mössbauer spectrum with an isomer shift of 0.197 mm/s and quadrupole splitting of 1.935 mm/s. Two crystalline forms of [Fe(TMP)(4-CNPy)(HIm)]ClO₄ have been characterized; the two forms differ only in the solvent content of the lattice. Crystal data for form A: $\mathrm{\text{a}}=$ 15.432 (12) Å, $\mathrm{\text{b}}=$ 20.696 (2) Å, $\mathrm{\text{c}}=$ 19.970 (5) Å, and $\beta =$ 99.256 (14)$deg$, monoclinic, space group P2₁/n, V $=$ 6295 (2) ų, Z $=$ 4, formula FeCl₃O₄N₈C${}_{69}$H${}_{69}$, 8397 observed data, ${\mathrm{\text{R}}}_1=$ 0.086, ${\mathrm{\text{wR}}}_2=$ 0.210, refinement on ${\mathrm{\text{F}}}^2$. Crystal data for form B: $\mathrm{\text{a}}=$15.267 (3) Å, $\mathrm{\text{b}}=$20.377 (6) Å, $\mathrm{\text{c}}=$ 19.670 (4) Å, and $\beta =$ 98.14 (1)$deg$, monoclinic, space group P$2_1$/n, V = 6058 (4) ų, Z = 4, formula C${}_{65.25}$H${}_{60.5}$Cl${}_{1.5}$FeN₈O₄, 5464 observed data, ${\mathrm{\text{R}}}_1=$ 0.096, ${\mathrm{\text{wR}}}_2=$ 0.112, refinement on F.

The OsO₄-mediated dihydroxylation of quinoline-annulated porphyrin generates a quinoline-annulated dihydroxychlorin in a regioselective fashion. Its dihydroxypyrroline moiety, located at the opposite of the annulated pyrrole, is susceptible to the same functional group interconversions we previously demonstrated for non-annulated dihydroxychlorins: oxidations to the corresponding dione, lactone, and dialkoxymorpholine derivatives. The quinoline-annulated chlorin and derivatives are all characterized by absorption spectra that are much broadened and between 130 and 220 nm red-shifted compared to their non-annulated analogs. Absorbance maxima in the NIR up to well above 800 nm were recorded. We attribute the bathochromic shift to their extended $\pi$-systems and inferred non-planarity, highlighting that quinoline-annulation is a particularly effective and simple strategy to red-shift the absorption spectra of chlorins and chlorin analogs.

Co(III) and Ga(III) complexes of 5,10-bis(pentafluorophenyl)corrole and 5,15-bis(pentafluorophenyl)corrole were synthesized by metalations with Co(OAc)₂ •4H₂O and GaCl₃, respectively. The structures of these complexes have been all unambiguously revealed by X-ray diffraction analysis. Their optical and electrochemical properties have been studied, which reveals small but distinctly different substituent effects depending upon the substitution positions.

Excited state dynamics, particularly intersystem crossing, of a set of meso-substituted porphyrins bearing different electron–donor and acceptor groups was studied by pulse train fluorescence technique. Triplet quantum yield was found to be critically dependent on the nature of meso-substituents in the porphyrin system. Porphyrins with meso methoxyphenyl groups were found to show high triplet quantum yields (${\varphi }_T$ between 0.70 and 0.81). Moreover, the quantity of methoxyphenyl groups and the substitution pattern directly influence ${\varphi }_T$. Alternatively, porphyrins attached to nitrophenyl group possess low triplet quantum yield values (~0.3). The observed structure-properties relationships suggest new ways for tuning the optical properties of porphyrins via chemical modification.

The synthesis of new porphyrins bearing external coordination sites and long alkyl chains is described. In particular, the possibility to use the Sonogashira coupling to introduce long alkynyl chains and the synthetic pathway to obtain these compounds is detailed. Two crystal structures of these new porphyrin derivatives were obtained. The synthesis of porphyrin dimers linked by a palladium(II) ion is also reported and some electronic consequences presented.

Photodynamic therapy (PDT) offers a new approach to selective tumor eradication. Modifications designed to increase and optimize efficacy continue to emerge. Selective photodamage to malignant cells and their environment can bring about tumor cell destruction, shutdown of the tumor vasculature, stimulation of immunologic anti-tumor effects and potentiation of other therapeutic effects. Current development of combination protocols may provide a better rationale for integration of PDT into clinical practice. An example described here is the ability of a sequential (two-sensitizer) PDT protocol to enhance the efficacy of photokilling. The first step involves low-level lysosomal photodamage that has been shown to promote the apoptotic response to subsequent photodynamic effects directed at mitochondria. In this report, we demonstrate the ability of Photofrin, an FDA-approved photosensitizing agent, to serve as either the first or second element of the sequential protocol.

An unusual feature of free base tetraarylporphyrins (H₂TArP) is the small amount of monocation (H₃TArP${}^{+})$ observed during titrations with acids. This anomalous behavior has been known for over forty years and has been explained in terms of the saddle deformation of the porphyrin that occurs upon protonation. In this paper, ¹H NMR spectroscopy is used to investigate the protonation of H₂OETPP, an H₂TArP that is pre-deformed into a highly nonplanar saddle structure by steric crowding of its peripheral substituents. The goal of our studies is to determine if the saddle structure of H₂OETPP stabilizes the monocation H₃OETPP${}^{+}$, and, if it does, to conduct detailed NMR studies of H₃OETPP${}^{+}$. NMR spectra clearly show the formation of H₃OETPP${}^{+}$ when one equivalent of acid is added to H₂OETPP in organic solvents, and for picric acid in toluene-d₈ the monocation is the dominant species (~70%). Crystals of H₃OETPP${}^{+}$ (picrate) suitable for X-ray crystallography could not be obtained, but the structure of H₄OETPP${}^{2+}$ (picrate)₂ was determined. Variable temperature NMR studies of H₃OETPP${}^{+}$ (picrate) reveal the presence of two dynamic processes. The first is picrate anion exchange in CD₂Cl₂, where the activation energy ($\mathrm{\Delta }$G${}^{‡})$ is calculated to be 53 kJ.mol${}^{-1}$. A second process, ND tautomerism ($\mathrm{\Delta }$G${}^{‡}=$ 42 kJ.mol${}^{-1})$ is also detected for D₃OETPP${}^{+}$ at very low temperatures in toluene-d₈. The much lower activation energy for ND tautomerism in D₃OETPP${}^{+}$ vs. D₂OETPP ($\mathrm{\Delta }$G${}^{‡}=$ 63 kJ.mol${}^{-1})$ may be due to destabilization of the ground state of the monocation due to the presence of cis interactions between the inner deuterium atoms.

As an extension of our study to reveal the effect of porphyrin deformation on the ${}^{13}$C and ¹H NMR chemical shifts, both five- and six-coordinate high-spin (S $=$ 2) Mn(III) complexes such as Mn(Por)Cl and [Mn(Por)(CD₃OD)₂]Cl have been prepared, where Por is a porphyrin dianion such as TPP, OMTPP, and T${}^i$PrP. Molecular structures of five-coordinate Mn(OMTPP)Cl and Mn(TⁱPrP)Cl have been determined by the X-ray crystallographic analysis. As expected, Mn(OMTPP)Cl and Mn(TⁱPrP)Cl have exhibited a highly saddled and highly ruffled porphyrin core, respectively. The ${}^{13}$C NMR spectra have revealed that these complexes generally exhibit the $\alpha$-pyrrole signals at the downfield positions and $\beta$-pyrrole an. meso signals at the upfield positions. The results suggest that the spin polarization of Mn(III)–N_P σ bonds, which occurs in all the high-spin Mn(III) complexes, is the major factor to determine the chemical shifts of the porphyrin carbon signals (Cheng, R.-J.; Chang, S.-H.; Hung, K.-C. Inorg. Chem. 2007; 46: 1948–1950). Although th. meso and $\alpha$-pyrrole signals are observed at the upfield and downfield positions, respectively, these signals are widely dispersed depending on the deformation mode of the porphyrin ring. The results have been explained in terms of the strong spin polarization of the Mn–N_P bond together with the specific metal-porphyrin orbital interactions such as: (i) the a2_u-d_z2 interaction in five-coordinate complexes, (ii) the a2_u-d_xy interaction in ruffled complexes, and (iii) the a_2u-d_x2_-y2 interaction in saddled complexes.

Photodynamic inactivation has been proposed as an efficient antimicrobial treatment for localized infections. Even though it is generally accepted that the cell wall and membrane components are the main targets of the photodynamic process, the importance of the nucleic acids as photodynamic targets is not yet fully understood. In this study, we investigated the photodamage of the genomic nucleic acids of the Gram negative bacterium Escherichia coli, using 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide (Tri-Py${}^{+}$-Me-PF) as photosensitizing agent. We tested, for the first time, the indirect photodamage effects on genomic DNA extracted from photosensitized bacteria and compared it with the direct effects on genomic DNA extracted from non-photosensitized cells, treated in otherwise similar experimental conditions. The results suggest that DNA does not seem to be a major target of photodynamic inactivation, once direct exposure to photosensitization does not damage DNA and does not significantly alter DNA concentration. The decrease in DNA concentration observed during the indirect exposure to photosensitization is directly related with the reduction of the concentration of bacterial cells. However, RNA synthesis was severely affected, once an indirect effect on proteins involved in the transcription process may cause a marked decrease in the RNA pool.

A presence of bulky 2,6-di-iso-propylphenoxy groups in bis-tert-butylisocyano adduct of 2(3),9(10),16(17),23(24)-tetrachloro-3(2),10(9),17(16),24(23)-tetra(2,6-di-iso-propylphenoxy)-phthalocyaninato iron(II) complex allows separation of two individual positional isomers and a mixture of the remaining two isomers using conventional chromatography. X-ray structures of “$D_{2h}$” and “$C_{4h}$” isomers were confimed by X-ray crystallography. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of each individual positional isomer allowed insight into their electronic structures and vertical excitation energies, which were correlated with the experimental UV-vis and MCD spectra.

The synthesis and in vitro evaluation of four mesoporphyrin IX-peptide conjugates designed to target EGFR, over-expressed in colorectal and other cancers, are reported. Two peptides with known affinity for EGFR, LARLLT (1) and GYHWYGYTPQNVI (2), were conjugated to mesoporphyrin IX (MPIX, 3) via one or both the propionic side chains, directly (4, 5) or with a triethylene glycol spacer (7, 8). The conjugates were characterized using NMR, MS, CD, SPR, UV-vis and fluorescence spectroscopies. Energy minimization and molecular dynamics suggest different conformations for the conjugates. SPR studies show that conjugate 4, bearing two LARLLT with no PEG spacers, has the greatest affinity for binding to EGFR, followed by conjugate 7with two PEG and two LARLLT sequences. Molecular modeling and docking studies suggest that both conjugates 4 and 7 can bind to monomer and dimer EGFR in open and closed conformations. The cytotoxicity and cellular targeting ability of the conjugates were investigated in human HEp2 cells over-expressing EGFR. All conjugates showed low dark- and photo-toxicities. The cellular uptake was highest for conjugates 4 and 8 and lowest for 7 bearing two LARLLT linked via PEG groups, likely due to decreased hydrophobicity. Among the conjugates investigated, 4 is the most efficient EGFR-targeting agent, and therefore the most promising for the detection of cancers that over-express EGFR.

Geometry, electronic and vibrational structure, and relative energies of different tautomeric forms have been calculated for free base corrphycene and its five tetra-, octa-, and dodeca-alkyl-substituted derivatives, of which only one has been synthesized so far. The results demonstrate that the lowest energy structure always corresponds to the transtautomeric form. Comparison with the experimental IR and X-ray data available for 2,3,6,7,11,12,17,18-octaethylcorrphycene shows, in contrast to previous suggestions, that th. transspecies is dominant both in solution and crystalline phase. Based on structural, spectral, and computational data, rates of double hydrogen transfer can be predicted. Tautomerization is expected to occur in a nanosecond or subnanosecond range. The rate should strongly decrease upon substituting parent corrphycene with alkyl groups at the pyrrolic $\beta$ positions, whereas the opposite effect is expected for mesosubstitution. Depending on the position of substituent, planar or nonplanar geometries of the corrphycene chromophore are predicted. The nonplanarity leads to a substantial increase of the intensity of the low energy electronic transitions (Q-bands).

A series of ruthenium phthalocyanine centered dendrimers has been prepared with up to 32 ethyl ester end groups. The photophysical properties have been assessed in THF to reveal a correlation between the degree of dendritic environment and the ability to generate singlet oxygen. In the attempt to prepare the correponding highly water-soluble polyelectrolyte dendrimers upon saponification we observed the cleavage of the central esters moieties adjacent to the pyridine unit in all cases. However, despite the lack of shielding by a growing branched shell surrounding the photoactive center, the obtained tetracarboxylate-terminated ruthenium phthalocyanine derivative was still able to generate singlet oxygen in aqueous medium.

“Non-fluorescent” chlorophyll catabolites (NCCs) were named “rusty pigments” originally, as they easily oxidized to yellow chlorophyll catabolites (YCCs) and other colored natural “phyllobilins.” In the present work, binding of Zn(II)-ions by YCC and its methyl ester YCC-Me, and structural investigations of the resulting Zn(II)-complexes are reported. Binding of Zn-ions to the weakly luminescent YCC or YCC-Me in DMSO produces orange-yellow complexes that exhibit strong green emission. The Zn-complex of YCC-Me was isolated and characterized by UV-vis-, fluorescence-, mass- and NMR-spectra. The data revealed a 2:1 complex, Zn(YCC-Me)${}_2$, in which YCC-Me serves as bidentate ligand. The Zn(II)-center in Zn(YCC-Me)${}_2$ is, thereby, deduced to be coordinated in a pseudo tetrahedral fashion. Formation of Zn(YCC-Me)${}_2$ (and of Zn(YCC)${}_2)$ is compatible with an isomerization of the lactam form of ring D to the corresponding lactim tautomer in these neutral Zn(II)-complexes.

An unsymmetrical phthalocyanine based one- and two-photon fluorescence imaging probe that substituted with 4-tert-butylphenoxy and RDGyK moieties was developed and characterized by UV-vis and high-resolution MALDI-TOF/MS. The conjugate is non-aggregated in $N$,$N$-dimethylformamide, with relatively weak fluorescence emission (${\mathrm{\Phi }}_F=$ 0.023) and high singlet oxygen quantum yield (${\mathrm{\Phi }}_{\mathrm{\Delta }}=$ 0.55). Conjugation of the cyclic peptide sequence c(RGDyK) can enhance the cellular uptake towards the DU145 and PC3 cells. While the fluorescence is greatly enhanced in mitochondria, the conjugate is non-cytotoxicity either in dark or upon exposure to red-light with dose up to 12 J.cm${}^{-2}$. The results suggest that this conjugate is a promising multifunctional imaging probe for mitochondria and cancer.

Novel boron complexes were synthesized by reacting cyclo[$m$]pyridine[$n$]pyrroles ($m+$ $n=$ 6) with BF₃. These complexes were characterized and studied by means of NMR, UV, and fluorescence spectroscopies, and X-ray crystallography. As compared to the non-boronated starting materials, the complexes of this study are more rigid and twisted, a feature that translates into a modulation of the optical features. Specifically, these boron complexes can be either strongly fluorescent or barely fluorescent, depending on the numbers of pyridine subunits contained within the macrocycle. The present approach could thus define an attractive and potentially generalizable means for modulating the inherent optical characteristics of expanded porphyrins.

Voltammetric sensors based on phthalocyanines have been used to detect a variety of compounds. In this paper, the state of the art of sensors prepared using classical techniques will be revised. Then, new strategies to improve the performance of the sensors will be described using as example sensors chemically modified with lutetium bisphthalocyanine (LuPc${}_2)$ dedicated to the detection of phenols of interest in the food industry. Classical LuPc₂ carbon paste electrodes can detect phenols such as catechol, caffeic acid or pyrogallol with limits of detection in the range of 10${}^{-4}$–10${}^{-5}$ M. The performance can be improved by using nanostructured Langmuir–Blodgett (LB) or Layer by Layer (LbL) films. The enhanced surface to volume ratio produce an increase in the sensitivity of the sensors. Limits of detection of 10${}^{-5}$–10${}^{-7}$ M are attained, which are one order of magnitude lower than those obtained using conventional carbon paste electrodes. Moreover, these techniques can be used to co-immobilize two electrocatalytic materials in the same device. The limits of detection obtained in LB sensors combining LuPc₂/AuNPs or LuPc₂/CNT are further improved. Finally, the LB technique has been used to prepare biosensors where a phenol oxydase (such as tyrosinase or lacasse) is immobilized in a biomimetic environment that preserves the enzymatic activity. Moreover, LuPc₂ can be co-immobilized with the enzyme in a lipidic film formed by arachidic acid (AA). LuPc₂ can act as an electron mediator facilitating the electron transfer. These biomimetic sensors formed by LuPc₂/AA/enzyme show Limits of detection of 10${}^{-8}$ M and an enhanced selectivity.

The tetraferrocenylporphyrin synthetic procedure was performed varying different reaction conditions. Mg, Mn, Pd and Cd complexes were synthesized and preliminarily studied. The results obtained show that the synthetic procedure strongly depends on catalyst, solvent and reagents concentration, even more than what observed with similar tetraarylporphyrins; concentration of substrates plays an important role in determining the outcome of the reactions.

A new subporphyrin namely, hydroxo-5,10,15-tri($N$-propyl-3-carbazolyl)subporphyri natoboron(III) 6 has been synthesized via the reported litreture procedure by the condensation of pyridine-tri-$N$-pyrrolylborane with 9-propyl-9H-carbazole-3-carbaldehyde. Its porphyrin analog $i.e$. 5,10,15,20-tetra($N$-propyl-3-carbazolyl)porphyrin has also been isolated from the reaction mixture, formed due to scrambling process and complexed with Zn(II). Photophysical properties of both subporphyrin and Zn(II)porphyrin have been studied in detail to confirm the intramolecular charge transfer process in subporphyrin analog. In addition, the ring contracted congener 6 also displays solid state fluorescence.

Organic nanoparticles (ONp) of an Fe(III) porphyrin appended with four $N$-polyethyleneglyco-pyridinium moieties prepared in acetonitrile were deposited onto hydrophilic or hydrophobic Si surfaces. Self-organized by intermolecular interactions, ONp reorganize in response to environmental changes. Mechanisms for the control of nanoparticle morphologies and surface patterning by varying surface energies are discussed.

Selective fluorescent and colorimetric sensing of cysteine in methanol-HEPES buffer (45 mM, pH $=$ 7.2, v/v $=$ 1/1) solution over various common amino acids and related thiol containing compounds has been achieved based on the cyclization reaction between the formyl group on 3-formylBODIPYs and cysteine/homocystein. Upon addition of cysteine/homocystein, 3-formylBODIPYs exhibited greatly enhanced fluorescence intensity as well as an abvious red-shift of the absorption peak (20–30 nm). The detection limits for cysteine were in the range of 1.18–2.73 $\times$10${}^{-6}$ M. The detection mechanism was studied by nuclear magnetic resonance and theoretical calculation.

Three $\beta$,$\beta \text{'}$-tetrabutano-substituted cobalt(III) triarylcorroles were synthesized and characterized by UV-vis, ¹H NMR spectroscopy and mass spectrometry as well as electrochemistry and spectroelectrochemistry. The examined compounds are represented as butano-(YPh)₃CorCo(PPh${}_3)$, where Cor represents the core of the corrole and Y is a CH₃, H or Cl group on the para-position of each meso-phenyl ring of the macrocycle. Each corrole undergoes two stepwise cobalt-centered reductions leading to formation of Co(II) and Co(I) derivatives in CH₂Cl₂ containing 0.1 M TBAP. Three reversible one-electron oxidations were observed within potential, ranging from 0.16 to 1.40 V in CH₂Cl₂. The first oxidation generates a mixture of Co(III) $\pi$-cation radical and Co(IV), while the second oxidation is metal-centered to give the Co(IV) corrole. Each cobalt corrole was examined as a catalyst for electroreduction of O₂ when coated on an edge-plane pyrrolytic graphite electrode in acidic and basic solutions. The results indicate that the cobalt tetrabutanotriarylcorroles can act as selective catalysts for the 2e reduction of molecular oxygen to give H₂O₂ as the final product under the given solution conditions.

Functionalization of corrole at its peripheral positions is an intriguing field of research, since the unusual reactivity of this macrocycle usually makes it difficult to predict the reaction products. We have investigated the introduction of halogen atoms at the corrole β-positions by using haloacids as reagents. Different behavior, in terms of number and position of the units introduced, was observed: chlorination yielded mono and disubstituted corrole, whereas bromination only afforded mono-substitution, even if on different positions. Iodination did not occur on the corrole free base, while the protection of the inner core by chelation with silver ion gave better results and a symmetric diiodinated corrole was isolated. 2D NMR analysis and X-ray crystallography provided useful information about the site of these corrole functionalizations.

A series of meso-aryloxy linked BODIPY monomers, dimers and trimer were synthesized by nucleophilic aromatic substitution (S_NAr) reaction from phenols with meso-chloro BODIPY and their photophysical properties were systematically studied by UV-vis and fluorescence spectroscopy. The relationship between their photophysical properties and the spatial arrangement of meso-aryloxy linked BODIPYs has been discussed. The monomers exhibited different extent solvent-dependent fluorescence, and fluorescence quenching in polar solvents were found relative to the HOMO energies of the donor (meso-phenols), indicating possible PET effect from meso-phenols to the BODIPY fluorophore. Ortho-dimer showed unusual broad red-shifted emission bands centered at 550 nm with a larger Stokes shifts at the range of 2900–3400 cm${}^{-1}$, and low fluorescence quantum yields, which was in sharp contrast to those of other dimers and trimer, indicating of possible excimeric species formation due to slipped cofacial arrangement ofortho-dimer.

Herein we report the synthesis of new gold nanoparticle-bacteriochlorin conjugate (Au-NP-PS) as a highly efficient photoacoustic (PA) imaging agent. The conjugate was obtained by reacting a water soluble thio-bacteriochlorin (derived from bacteriochlorophyll-$a)$ with Au-NP. The resulting NPs were characterized by UV-vis, TEM (transmission electron microscopy)/HRTEM (high resolution TEM) and diffraction pattern. The results obtained from in vitro studies suggest that due to conjugation between the PS and Au-NPs, the photoacoustic (PA) signals from the Au-NP-PS were greatly enhanced by a factor of 2.4 compared to that from PS alone.

A phthalocyanine-chalcone conjugate was previously reported to retain the full photodynamic activity of the phthalocyanine and a slightly lowered antivascular effect of the chalcone. Assuming that it was due to an insufficient release of the chalcone, we described here several grafting modes applied to the preparation of phthalocyanine-chalcone conjugates.

An analysis of the MCD spectroscopy and TD-DFT calculations of magnesium tetra-(15-crown-5-oxanthreno)-phthalocyanine is reported. This study provides a reassessment of an earlier study on the nature of the bands in UV-visible absorption spectra of magnesium and zinc tetra-(15-crown-5-oxanthreno)-phthalocyanine that was based on an analysis of TD-DFT calculations for a series of model complexes with the B3LYP functional. A detailed analysis of MCD spectral data and TD-DFT calculations with the CAM-B3LYP functional for the complete Mg(II) complex provides an additional insight into the optical properties and electronic structures of tetra-(15-crown-5-oxanthreno)-phthalocyanines. Thus, the bands in the Q-band region are reassigned as being due exclusively to the Q transition of Gouterman’s 4-orbital model, since intense pseudo-${\mathcal{𝒜}}_1$ terms are observed in the MCD spectrum in a spectral region that had previously been assigned as charge transfer bands.

Preparation and characterization of a small library of symmetric trans-di(4-pyridyl)porphyrin dimers, obtained by either Glaser–Hay or Sonogashira coupling reactions from appropriately prepared trans-di-4-pyridylporphyrin precursors, is presented. The porphyrin dimers are differentiated by a phenyl-alkynyl bridge of increasing length at one meso-position, while for all the derivatives the two remaining opposite meso-positions are tailored with a phenyl moiety bearing a short polyether chain. Coordination of the four pyridyl groups with appropriate metal fragments may be exploited to construct tubular hollow structures, with varied internal sizes, depending on the choice of the porphyrin dimer component.

A thoroughly structural characterization of (TTC)GePh (TTC $=$ 5,10,15-tritolylcorrole; Ph $=$ phenyl) in solution has been carried out through a combination of 2D NMR (¹H-¹H COSY, ¹H-¹H ROESY, ¹H-${}^{13}$C HSQC and ¹H-${}^{13}$C HMBC) experiments and density functional theory (DFT) calculations of the molecular and electronic structure and the shielding constants. The ¹H and ${}^{13}$C chemical shifts computed at DFT-S12g and DFT-SAOP levels of theory nicely reproduce the experimental values, the agreement between theory and experiment being especially good for the DFT-S12g results. The calculations prove to be able to capture the fine details of the NMR spectra and to resolve some assignment ambiguities related to the inherent conformational flexibility of the macrocycle. The calculations also provide an explanation of the observed chemical shift trends in terms of diamagnetic and paramagnetic components of the shielding tensor.

Herein, we report a photochemical hydrogen evolution system consisting of various cobalt based catalysts, a metallated Sn porphyrin as photosensitizer and a triethanolamine as a sacrificial electron donor in acetonitrile/H₂O (1:1) solution. Since a tin metallated porphyrin is used for the first time as photosensitizer in this type of systems, a systematic study was performed in order to elucidate the best conditions for H${}_2$production. Upon visible irradiation hydrogen production was detected with the best result obtained at pH 7 with a TON of 150, after 100 h in the presence of catalyst 1. Moreover, when TiO₂ nanoparticles were added at the catalytic system 2 the hydrogen production was increased from 53 TON to 131 TON, under the same experimental conditions.

Novel benzoporphyrins bearing pyridine or pyridine-$N$-oxide groups were prepared through a concise method based on a Pd⁰ catalyzed cascade reaction. These benzoporphyrins were examined as sensitizers for dye-sensitized solar cells. Vicinal pyridine and vicinal pyridine-$N$-oxide groups were introduced as new types of anchoring/acceptor groups for dye-sensitized solar cells for the first time. While all the porphyrins showed solar to electricity conversion, benzoporphyrins bearing pyridine-$N$-oxide anchoring groups displayed higher conversion efficiency than benzoporphyrins bearing pyridine-anchoring groups.Opp-dibenzoporphyrins display broadened and red-shifted UV-vis absorption and emission bands as compared with those of the monobenzoporphyrins, which arises from the fusion of one more benzene ring and the attachment of two more electron-withdrawing groups to the porphyrin $\beta$-positions. Cyclic voltammetry (CV) data and DFT calculation data obtained for these porphyrins agree well with their UV-vis absorption and fluorescence spectroscopic data. The HOMO energy level derived from the first oxidation potentials indicate that regeneration of the resulting porphyrin radical cation by the redox mediator (I${}^{-}$/I${}_3^{-})$ is thermodynamically feasible for all these benzoporphyrin sensitizers (3, 5, 8 and 10). On the other hand, excited state energy levels of these benzoporphyrins calculated from the CV data, the UV-vis and fluorescence spectroscopic data are all slightly lower than the energy level of the conduction band of TiO₂, suggesting insufficient driving force for efficient electron injection from the porphyrin excited singlet state to the conduction band of TiO₂.

Ferrochelatase catalyzes the insertion of ferrous iron into protoporphyrin IX to generate heme. Despite recent research on the reaction mechanism of ferrochelatase, the precise roles and localization of individual active site residues in catalysis, particularly those involved in the insertion of the ferrous iron into the protoporphyrin IX substrate, remain controversial. One outstanding question is from which side of the macrocycle of the bound porphyin substrate is the ferrous iron substrate inserted. Pre-steady state kinetic experiments done under single-turnover conditions conclusively demonstrate that metal ion insertion is pH-dependent, and that the conserved active site His-Glu pair coordinately catalyzes the metal ion insertion reaction. Further, p$K_a$ calculations and molecular dynamic simulations indicate that the active site His is deprotonated and the protonation state of the Glu relates to the conformational state of ferrochelatase. Specifically, the conserved Glu in the open conformation of ferrochelatase is deprotonated, while it remains protonated in the closed conformation. These findings support not only the role of the His-Glu pair in catalyzing metal ion insertion, as these residues need to be deprotonated to bind the incoming metal ion, but also the importance of the relationship between the protonation state of the Glu residue and the conformation of ferrochelatase. Finally, the results of this study are consistent with our previous proposal that the unwinding of the $\pi$-helix, the major structural determinant of the closed to open conformational transition in ferrochelatase, is associated with the Glu residue binding the Fe${}^{2+}$ substrate from a mitochondrial Fe${}^{2+}$ donor.