Journal of Porphyrins and Phthalocyanines

The preparation and optical properties of peripherally substituted phthalocyanines and their analogs (i.e. naphthalocyanines, anthracyanines, aza-analogs of phthalocyanines, and tetraazaporphyrins) have been widely discussed. This review highlights methodologies that have been published in poorly known and mostly unavailable Russian journals.

Reported here is the synthesis of new binuclear rhodium(III) and iridium(III) semi-sandwich complexes of a Schiff-base expanded porphyrin. Single crystals of these new complexes were subject to X-ray diffraction analysis. The resulting structures revealed that the Schiff-base macrocycle adopts a V-shape in which two {(η⁵-C₅Me₅)MCl} (M = Rh and Ir) fragments are accommodated within the macrocyclic pocket. The coordination environment of the metal centers is typical to that of "piano stool"-type complexes. The X-ray analyses and complementary NMR studies (carried out in CD₂Cl₂) provide evidence for the existence of strong intramolecular hydrogen-bonding interactions between the pyrrolic NH protons and the chloride counteranion both in solution and in the solid state.

Phthalocyanines are used as various applications, including as organic charge carriers in photocopiers, laser light absorbers in data storage systems, photoconductors in photovoltaic cells and electrochromic displays, and non-colored transparent film in visible region. The absorption maxima of phthalocyanines are best if moved near the infrared region for these applications. The Q band of phthalocyanines can be moved to bathochromic effects through extension of a π conjugation system such as naphthalocyanines and anthracyanines. Yields of naphthalocyanines and anthracyanines are, however, low. To solve the problem, novel metal phthalocyanines having non-peripheral S-aryl substituent were synthesized. The novel phthalocyanines show a high strain structure and no liquid crystal property. The target compounds were synthesized: 15 phthalocyanines from 2,3-dicyanohydroquinone in 3 steps via 1,2-dicyanobenzene-3,6-bis(trifluorate) and 1,2-dicyanobenzene-3,6-thiophenols. The Q bands of obtained compounds appeared in the near-infrared region. In particular, lead 1,4,8,11,15,18,22,25-octakis(thiophenylmethyl)phthalocyanine shows a Q band at 857 nm. Furthermore, non-colored transparent films in the visible region can be produced.

Recent discoveries from our research groups on the photophysics of a few cofacial bisporphyrin dyads for through space singlet and triplet energy transfers raised several important investigations about the mechanism of energy transfers and energy migration in light-harvesting devices, notably LH II, in the heavily investigated purple photosynthetic bacteria. The key feature is that for face-to-face and slipped dyads with controlled structure using rigid spacers or spacers with limited flexibilities, our fastest rates for singlet energy transfer are in the 10 × 10⁹s^-1 (i.e. 100 ps time scale) for donor-acceptor distances of ~3.5–3.6 Å. The time scale for energy transfers between different bacteriochlorophylls, notably B800*→B850, is in the ps despite the long Mg⋯Mg separation (~18 Å). This short rate drastically contrasts with the well-accepted Förster theory. This review focuses on the photophysical processes and dynamics in LH II and compares these parameters with our investigated model dyads build upon octa-etio-porphyrin chromophores and rigid and semi-rigid spacers. The recently discovered role of the rhodopin glucoside (carotenoid) will be analyzed as possible relay for energy transfers, including the possibility of uphill processes at room temperature. In this context the concept of energy migration may be complemented by parallel relays and uphill processes. It is also becoming more obvious that the irreversible electron transfer at the reaction center (electron transfer from the special pair to the phaeophytin) renders the rates for energy transfer and migration faster precluding all possibility of back transfers.

μ-(dihydroxo)dipalladium(II) complex with N²¹, N²²-etheno bridged tetraphenylporphyrin ligand was employed in the catalytic photooxidation of phenol derivative in aerated homogeneous solution with visible light irradiation. The Pd complex promoted the degradation of p-tert-butylphenol as well as Cu phthalocyanine under basic conditions and it worked as a photosensitizer even in neutral conditions in contrast with Cu phthalocyanine. Some phenol derivatives afforded corresponding quinones selectively in this photooxidation. The present Pd complex coordinated by the bidentate porphyrin ligand showed higher photosensitizing ability than tetraphenylporphyrin free-base and ordinary tetradentate tetraphenylporphyrin palladium(II) complex for photooxidation of 2,6-di-tert-butylphenol. This bidentate Pd complex showed higher light durability even under the conditions where photodegradation of porphyrin free-base and tetradentate Pd porphyrin were observed by extensive irradiation.

The tetrasulfonated Cu^II(tspc)^4-, tspc = 4,4′,4″,4‴-phthalocyaninetetrasulfonate, and the trisulfonated Co^II(trspc)^3-, trspc = n,n′,n″-phthalocyanine-trisulfonate and n, n′ and n″ indicate the sulfonated positions of the various isomers, were covalently linked to a polyethyleneimine, M_n ~ 10000 and M_w ~ 25000, backbone. A fraction of the amine groups in a strand was converted to Cu^IIpc(-SO₃)₃(-SO₂N<)^\3- or Co^IIpc(-SO₃)₂(-SO₂N<)^\2- pendants and the remaining were acetylated. Strands of the polymers, poly(K₃Cu^IItspc) and poly(K₂Co^IItrspc), formed spherical bundles with diameters ~1000 nm for poly(K₃Cu^IItspc) and ~100 nm for poly(K₂Co^IItrspc). The stability of the bundles is metal-dependent. Poly(K₂Co^IItrspc) forms the most stable bundles with respect to hydrolytic and redox reactions. ESR and optical spectroscopies as well as reactions of the pendants with pulse radiolytically generated radicals, namely e^-_sol, C^•H₂OH, (CH₃)₂COHC^•H₂, CO₂^•-, N₃^• and SO₄^•-, revealed a distribution of pendants between isolated and aggregated forms in a bundle. The reduction of the Cu(II) to Cu(I) in aqueous solutions of the poly(K₃Cu^IItspc) was associated with pendants present in a mostly hydrophobic environment. Unstable phthalocyanine pendants with Co^III-carbon bonds are formed when Co^IIpc(-SO₃)₂(-SO₂N<)^\2- reacted with C-centered radicals, (CH₃)₂COHC^•H₂ and C^•H₂OH. The species with Co^III-carbon bonds were precursors to the formation of Co^Ipc(-SO₃)₂(-SO₂N<)^\3- pendants. The redox reactions of the pendants in these polymers are compared with those of K₄Cu^IItspc and K₃Co^IItrspc.

The zinc and magnesium metalated derivatives of 5,5′-[12,12′-di(thiododecyloxy)-4,4′-phenyl)]-10,10′,15,15′,20,20′-hexakis(3,3′,4,4′,5,5′-hexakisdecyloxyphenyl)diporphyrin, 1b and 1c, have been synthesised and deposited to form self-assembled monolayer (SAM) films on the surface of gold-coated glass substrates. The SAM films have been characterized by RAIR spectroscopy and fluorescence spectroscopy. The potential for the porphyrin films to catalyze the oxidation of tryptophan within human serum albumin upon irradiation with white light has been demonstrated and attributed to the porphyrins acting as photosensitizers of oxygen to form oxidizing species.

This paper is no longer available. Please contact jpp@wspc.com

A novel Co(II) porphyrin lipoic acid derivative was synthesized starting from the commerically available red blood pigment hemin. The disulfide functionalities of the lipoic acid moieties allowed its immobilization on gold by a self-assembly method. The Co(II) porphyrin self-assembled monolayer (SAMs) on gold (111) surfaces were characterized electrochemically through monolayer reductive desorption and evaluation of the redox properties of the immobilized molecules in organic medium, and by scanning tunneling microscopy (STM). It was found that after assembly the Co(II) porphyrin is electroactive exhibiting the typical redox processes observed for its precursor without the appended lipoic acid in solution. A coverage of 2.7 × 10^-10mol.cm^-2 has been estimated assuming that four electrons (one per each sulfur atom) are involved in the process. The porphyrin-modified gold electrodes exhibit catalytic acitivity demonstrated towards the reduction of molecular oxygen in acidic solution.

Three novel tetrathiafulvalene-annulated metalloporphyrazines with electron-withdrawing pentoxycarbonyl groups at the periphery were synthesized via the cyclotetramerization of dipentyl 6,7-dicyanotetrathiafulvalen-2,3-dicarboxylate in the presence of corresponding metal salts (Zn(OAc)₂·2H₂O, Cu(OAc)₂·2H₂O, and NiCl₂) and in pentanol. Molecular structures were fully characterized by ¹H NMR, FT-IR, UV-vis, MALDI-TOF mass spectra and elemental analysis. These newly synthesized macrocyclic dyes were sufficiently stable in air during the purification process and also in further experiments. Electron-withdrawing substituents reduced the ability of tetrathiafulvalene groups to form radical cations. Solution electrochemical data showed one reductive and three oxidative processes within a -2000 mV to +2200 mV potential window. The four couples observed were assigned to Pz^-2/Pz^-3 (I), TTF^+•/TTF (II), TTF⁺²/TTF^+• (III) and Pz^-1/Pz^-2 (IV).

Syntheses, molecular structures and magnetic susceptibilities of three meso-substituted high-spin iron(III) porphyrinate complexes ([Fe(TEtP)(Cl)], [Fe(TPrP)(Cl)], and [Fe(THexP)(Cl)]) are described. It was determined that the inter-ring interactions within each dimeric unit change upon alteration of the alkyl groups at the meso positions. Magnetic exchange couplings between iron centers of the dimers are in accord with the trends in structural inter-ring geometries. Crystal data for [Fe(TEtP)(Cl)]: a = 10.1710(5) Å, b = 11.309(3) Å, c = 12.170(3) Å, α = 91.774(9)°, β = 113.170(14)°, γ = 112.149(9)°, V = 1165.2(4) ų, triclinic, , Z = 2, R₁ = 0.0844 and wR₂ = 0.2073 for observed data. Crystal data for [Fe(TPrP)(Cl)]: a = 13.040(2) Å, b = 15.221(2) Å, c = 14.6681(9) Å, β = 109.997(11)°, V = 2735.9(7) ų, monoclinic, P2₁/n, Z = 4, R₁ = 0.0477 and wR₂ = 0.1176 for observed data. Crystal data for [Fe(THexP)(Cl)]: a = 10.246(7) Å, b = 12.834(4) Å, c = 17.420(15) Å, α = 69.74(3)°, β = 87.52(4)°, γ = 84.89(3)°, V = 2140(2) ų, triclinic, , Z = 2, R₁ = 0.1024 and wR₂ = 0.2659 for observed data.