Journal of Porphyrins and Phthalocyanines

The dihydroisoindole strategy for the synthesis of linearly annelated π-extended porphyrins is a common approach to tetrabenzo-, tetranaphtho-, and tetraanthraporphyrins with variable functionality and substitution patterns. This method implies the use of a common type of precursors involving the 4,7-dihydroisoindole moiety, which are the closest possible stable relatives of the unstable isoindole, benzoisoindole and naphthoisoindole. A key feature of this strategy is the unprecedented mildness of the final oxidative aromatization step, which accounts for synthetic versatility, better functional group tolerance and high purity of the products. Many new linearly annelated π-extended porphyrins of the tetrabenzo-, tetranaphtho-, and tetraanthraporphyrin families were produced and characterized for the first time, including soluble planar and highly emissive 5,15-diaryl derivatives. The double bond of the dihydroisoindole fragment can also be useful for further modification of the porphyrin by means of addition of cycloaddition reactions, leading to new, previously inaccessible porphyins bearing multiple halide, hydroxy, or acetoxy groups at the periphery.

Over fifty years ago, Linstead and Elvidge described the syntheses of phthalocyanine-like macrocycles in which one or two of the interior metal-binding nitrogen atoms were replaced with aromatic C-H groups. We review here the coordination chemistry of two of these systems, dicarbahemiporphyrazine and benziphthalocyanine, and we emphasize the unusual reactivity displayed by these macrocycles and the varying extent to which the C-H groups are activated by metal-binding.

This paper is a summary of the lecture Michael Hanack gave at the 5th ICPP meeting in Moscow. A new method for the preparation of phthalonitriles is reported which makes the syntheses of substituted phthalocyanines much easier. Then the generation of highly reactive dehydrophthalocyanines using different methods is described. The reaction of these intermediates with dienophiles and various solvents is also discussed. In the last section, the syntheses of tetra- and octa- Zn phthalocyanine and -naphthalocyanine carbohydrate conjugates, which will be used for photosensitizers in PDT, is reported.

Calix[4]pyrroles have attracted considerable attention within the macrocyclic, supramolecular, and porphyrin analog communities due to their ability to act as simple-to-synthesize receptors for common anions, such as chloride and fluoride. Reported here is what we believe is a new, potentially generalizable route to fully β-alkyl substituted calixpyrroles. These products are accessible from the starting pyrrolic esters, and are obtained via simple reaction with CH₃Li, followed by subsequent quenching with HCl in ether. A representative system has been characterized by X-ray diffraction analysis. The present route allows access to calix[4]pyrroles bearing functionality, such as double bonds, off the so-called C-rim; such systems are of interest because they could allow for further synthetic elaborations and permit incorporation of calix[4]pyrroles into more complex structures.

The reversible control of dual (or multiple) states of molecules and supramolecules has attracted much attention for molecular switch, sensor, memory, logic gate, and molecular machine applications. In this paper, a ligand-induced sliding system using a complementary porphyrin-phthalocyanine dimer accompanied by a large fluorescence change is described. An imidazole-appended porphyrinatozinc-phthalocyaninatomagnesium complex 5 was synthesized by the palladium-catalyzed coupling reaction of the corresponding porphyrin and phthalocyanine moieties. The imidazole group of 5 coordinated to the magnesium ion of another 5 was formed spontaneously and dominantly to give a stacked dimer 5ST in non-coordinating solvents, such as chloroform, even at submicromolar concentration (< 10^-6 M). When an appropriate amount of dimethyl sulfoxide (DMSO) was added to the 5ST solution, the stacked dimer was transformed almost quantitatively into the extended dimer 5Ex. This transformation was monitored by UV-vis and fluorescence spectroscopies. In the UV-vis spectra, the porphyrin's Soret band is split characteristically because of excitonic coupling between the two closely located porphyrins in 5Ex. At the same time, the fluorescence intensity of 5Ex at 700 nm (ex. 414 nm) increased by a factor of 28 compared with that of 5ST. Removal of the DMSO molecules by extraction with water from the system regenerated 5ST almost completely from 5Ex, and the fluorescence was quenched again. The reversible system can be repeated by cycles of addition and removal of DMSO. The present system can be classified as a coordination-induced sliding system accompanied by a large fluorescence change, and may be applied as a fluorescence-based molecular switch.

Glucose-, galactose- and lactose-containing photosensitizers based on derivatives of chlorophyll a and bacteriochlorophyll a were synthesized with the use of [3+2] cycloaddition between sugar azides and triple bond derivatives of chlorins and bacteriochlorins. Unlike bacteriochlorin cycloimide, chlorin was detected to form a Cu-complex during the click reaction. An approach to the synthesis of metal-free glycosylated chlorins was developed with the use of "protection" by Zn²⁺ cation and subsequent demetalation. It is based on the action of alkynyl chlorin e₆ derivative Zn-complex, which is resistant to the substitution by copper cation. Bacteriochlorin p cycloimide conjugate with per-acetylated β-D-lactose was obtained and shown to become water-soluble after unblocking of the lactose hydroxy functions. NMR studies allowed for the elucidation of structure, tautomeric form and conformation of the obtained compounds.

Water soluble zwitterionic, as well as cationic and anionic triazatetrabenzcorroles (TBC), phthalocyanines (Pc) and a porphyrin (P) were synthesized and their sensitizer properties investigated. Monomerization of the sensitizers, including their mixtures, in the presence of a detergent was used as a basis for studying the fundamental effect of co-sensitization upon a known model reaction, viz. the photooxidation of 2-mercaptoethanol in aqueous alkaline solutions. Compared to single-component sensitizers, a remarkable improvement of the photocatalytic activity is observed in the case of co-sensitization employing molecules that absorb in different Q and Soret regions.

The azomethine ylide generated from the reaction of a corrole-3-carbaldehyde and N-methylglycine was trapped with dimethyl fumarate, dimethyl acetylenedicarboxylate and fullerene C₆₀ in 1,3-dipolar cycloadditions. A similar azomethine ylide generated from a corrole-2-carbaldehyde was trapped with 1,4-naphthoquinone, yielding the expected dehydrogenated 1,3-dipolar cycloadduct and a quinone-fused corrole derivative. A detailed synchrotron single-crystal X-ray diffraction analysis of the gallium(III)(pyridine) complex of 5,10,15-tris(pentafluorophenyl)corrole-3-carbaldehyde is also presented.

Two unsymmetrical Zn(II) phthalocyanines 1 and 2 bearing an anchoring carboxylic function linked to the phthalocyanine ring through different rigid arylenevinylene bridges have been designed for dye-sensitized solar cell (DSSC) applications. The phthalocyanines 1 and 2, when anchored onto nanocrystalline TiO₂ films, yielded 30% incident monochromatic photon-to-current conversion efficiency (IPCE) and 2% power conversion efficiencies under AM1.5 sun.

The effects of 9-substitution on the photophysical properties of tetraphenylporphycenes (TPPo) have been examined using an electron acceptor, an electron donor, and an electroneutral substituent as model compounds. Introduction of the acetoxy group enhances the fluorescence ability of the compound, with only a small reduction in the singlet oxygen quantum yield. The optical and photophysical properties of a nitro-porphycene are reported for the first time. The compound is emerald green, contrasting with the typical blue color of porphycenes. While this compound is much less fluorescent than unsubstituted TPPo, its singlet oxygen quantum yield is only slightly lower, almost identical to that of the 9-acetoxy compound (9-AcOTPPo). Finally, the electron-donor amino group is found to induce the greatest changes in the porphycene photophysics, decreasing strongly its fluorescence and singlet oxygen quantum yields. With the exception of such electron donors, introduction of substituents at the 9 (meso) position of tetraphenylporphycenes is not detrimental to their photophysics and photosensitizing ability and thus can be exploited for targeted photodynamic therapy purposes.

The title complex cation, [Sb(pc)(OH)₂]⁺, (pc = phthalocyaninate, C₃₂H₁₆N₈^2-) has been prepared by oxidizing [Sb(pc)]I₃ with tert-butyl perbenzoate and isolated as hexafluorophosphate and triflate salts. These salts are relatively well-soluble in polar solvents (e.g.CH₂Cl₂, acetonitrile, acetone) without detectable aggregation. In particular, they dissolve relatively well in ethanol and methanol in which [Sb(pc)Br₂]⁺ or [Sb(pc)Cl₂]⁺ salts are poorly soluble whereas they have extremely low solubility in 1-chloronaphthalene and CHCl₃, unlike the bromo or chloro analogs. The spectral properties of [Sb(pc)(OH)₂]⁺ have been investigated by optical absorption and magnetic circular dichroism spectroscopy. Although its Q band tends to appear at a longer wavelength in a solvent with a larger refractive index, as is the case for its Br and Cl analogs, the Q band positions in donor solvents deviate considerably from linear correlation between Onsager's solvent polarity function. In the Soret band region, spectra of [Sb(pc)(OH)₂]⁺ are different in CH₂Cl₂ and acetonitrile, particularly around the B1/B2 bands, unlike the bromo and chloro analogs. The solvent dependence of absorption spectra and the difference in solubility suggests that the presence of the axial hydroxyl groups endows the phthalocyanine macrocycle with considerable hydrophilicity. It also suggests that there are some specific chemical interactions between the axial hydroxyl groups and the surrounding donor solvent molecules.

A new process leading to 1-(acridin-9-yl)dipyrranes has been elaborated. The titled skeleton is assembled in a convergent fashion from 5-aryl substituted dipyrranes and acridine via a nucleophilic addition, followed by the oxidation of adducts, which are formed in situ. These products were transformed into respective 1-(acridin-9-yl)dipyrrins via 2,3-dichloro-4,5-dicyano-1,4-benzoquinone mediated oxidation. Spectroscopic studies were conducted which revealed large Stokes shifts in 1-(acridin-9-yl)dipyrranes and led to the conclusion that there is a significant conjugation between both moieties in molecules of 1-(acridin-9-yl)dipyrrins.