Phthalocyanine Radical Anions Research Articles

Molecular Structure, Optical and Magnetic Properties of Dianionic Free‐Base Tetrapyrazinoporphyrazine Macrocycle

AbstractFree‐base tetrapyrazinoporphyrazine (H2TPyzPz) has been synthesized and the reduction of this macrocycle by an excess of sodium fluorenone ketyl in the presence of 2.2.2‐cryptand yields {Na(2.2.2‐cryptand)}2(H2TPyzPz)⋅2C6H4Cl2 (1) salt containing H2TPyzPz2‐ dianions. Blue shift of both Soret and Q‐bands is observed in the spectrum of 1 and a new band is observed at 822 nm. Reduction is accompanied by alternation of the C‐Nimine bonds in the macrocycle. The difference between short and long bonds of 0.092 Å is essentially higher than that for free‐base phthalocyanine radical anions (0.040 Å). This difference can be explained by population of LUMO of H2TPyzP by two electrons in singlet ground state. According to the calculations distortion almost disappears in triplet excited state since in this state two additional electrons occupy orbitals which bonding and antibonding properties are interchanged. Salt 1 shows a weak narrow EPR signal indicating diamagnetism of H2TPyzPz2‐. Calculations also show singlet ground state for the dianions whereas the excited triplet state is positioned by 1130 K higher than the ground state and is not populated at room temperature.

Salts with titanyl and vanadyl phthalocyanine radical anions. Molecular design and effect of cations on the structure and magnetic and optical properties

Our recent data on radical anion salts of titanyl (TiIVOPc) and vanadyl (VIVOPc) phthalocyanines as well as additional new data are summarized.

Defining the conditional basis of silicon phthalocyanine near-IR ligand exchange.

Bond cleavage reactions initiated by long-wavelength light are needed to extend the scope of the caged-uncaged paradigm into complex physiological settings. Axially unsymmetrical silicon phthalocyanines (SiPcs) undergo efficient release of phenol ligands in a reaction contingent on three factors - near-IR light (690 nm), hypoxia, and a thiol reductant. These studies detail efforts to define the mechanistic basis for this unique conditionally-dependent bond cleavage reaction. Spectroscopic studies provide evidence for the formation of a key phthalocyanine radical anion intermediate formed from the triplet state in a reductant-dependent manner. Computational chemistry studies indicate that phenol ligand solvolysis proceeds through a heptacoordinate silicon transition state and that this solvolytic process is favored following SiPc radical anion formation. These results provide insight regarding the central role that radical anion intermediates formed through photoinduced electron transfer with biological reductants can play in long-wavelength uncaging reactions.

Interligand Charge Transfer in a Complex of Deprotonated cis-Indigo Dianions and Tin(II) Phthalocyanine Radical Anions with Cp*IrIII.

A diamagnetic complex, {(cis-indigo-N,N)2-(Cp*IrIII)} (1), in which deprotonated cis-indigo dianions coordinate an iridium center through two nitrogen atoms was obtained. By employment of the ability of the iridium center in 1 to coordinate an additional ligand, the complex [(Bu4N+)2{[SnII(Pc•3-)](cis-indigo-N,N)2-Cp*IrIII}•-2·0.5(H2Indigo)·2.5C6H4Cl2 (2), which has two functional ligands coordinating an IrIII center, was obtained. This complex has a magnetic moment of 1.71 μB at 300 K, in accordance with an S = 1/2 spin state. The spin density is mainly delocalized over the Pc•3- macrocycle and partially on (cis-indigo-N,N)2-. Due to an effective π-π interaction, a thermally activated charge transfer from [SnII(Pc•3-)]•- to (cis-indigo-N,N)2- is observed, with an estimated Gibbs energy (-ΔG°) of 9.27 ± 0.18 kJ/mol. The deprotonation of indigo associated with the coordination of IrIII by the indigo releases H+ ions, which protonate noncoordinating indigo molecules to produce leuco cis-indigo (H2Indigo). One H2indigo links two (cis-indigo-N,N)2- dianions in 2 to produce strong N-H···O═C and O-H···O═C hydrogen-bonding interactions.

IR absorption spectroscopic characteristics of peripherally substituted thiophenyl phthalocyanine in sandwich bis(phthalocyaninato) complexes

The IR spectra data for a series of thirteen rare earth double-deckers M[Pc(SPh)8]2 (M=Y, Ce⋯Lu, except La and Tm) have been collected and detailed characterized. The electronic absorption spectra showed that the Soret and Q bands are blue-shifted, and especially the Q bands at 705–726nm clearly become stronger along with the decrease of rare earth ion radius. For MIII[Pc(SPh)8]2, the Infrared characteristic absorption peaks for the phthalocyanine anion radical [Pc(SPh)8]− were observed at 1311–1323cm−1 as the strongest absorption bands, which can be ascribed to the pyrrole stretching. As for the Ce[Pc(SPh)8], the marker absorption bands at 1335cm−1 was observed. In addition, the typical IR absorption bands of phthalocyanine radical anion [Pc(SPh)8]− move to the high energy as the decrease of rare earth metal ionic radius. These facts suggest that the π-π electron interaction in these double-deckers becomes stronger along with the lanthanide contraction.

Tetrabutylammonium Salts of Aluminum(III) and Gallium(III) Phthalocyanine Radical Anions Bonded with Fluoren-9-olato- Anions and Indium(III) Phthalocyanine Bromide Radical Anions.

Reduction of aluminum(III), gallium(III), and indium(III) phthalocyanine chlorides by sodium fluorenone ketyl in the presence of tetrabutylammonium cations yielded crystalline salts of the type (Bu4 N+ )2 [MIII (HFl-O- )(Pc.3- )].- (Br- )⋅1.5 C6 H4 Cl2 [M=Al (1), Ga (2); HFl-O- =fluoren-9-olato- anion; Pc=phthalocyanine] and (Bu4 N+ ) [InIII Br(Pc.3- )].- ⋅0.875 C6 H4 Cl2 ⋅0.125 C6 H14 (3). The salts were found to contain Pc.3- radical anions with negatively charged phthalocyanine macrocycles, as evidenced by the presence of intense bands of Pc.3- in the near-IR region and a noticeable blueshift in both the Q and Soret bands of phthalocyanine. The metal(III) atoms coordinate HFl-O- anions in 1 and 2 with short Al-O and Ga-O bond lengths of 1.749(2) and 1.836(6) Å, respectively. The C-O bonds [1.402(3) and 1.391(11) Å in 1 and 2, respectively] in the HFl-O- anions are longer than the same bond in the fluorenone ketyl (1.27-1.31 Å). Salts 1-3 show effective magnetic moments of 1.72, 1.66, and 1.79 μB at 300 K, respectively, owing to the presence of unpaired S=1/2 spins on Pc.3- . These spins are coupled antiferromagnetically with Weiss temperatures of -22, -14, and -30 K for 1-3, respectively. Coupling can occur in the corrugated two-dimensional phthalocyanine layers of 1 and 2 with an exchange interaction of J/kB =-0.9 and -1.1 K, respectively, and in the π-stacking {[InIII Br(Pc.3- )].- }2 dimers of 3 with an exchange interaction of J/kB =-10.8 K. The salts show intense electron paramagnetic resonance (EPR) signals attributed to Pc.3- . It was found that increasing the size of the central metal atom strongly broadened these EPR signals.

Molecular structure, optical and magnetic properties of the {SnIVPc(3-)Cl2}•- radical anions containing negatively charged Pc ligands

Radical anion salt ( PPN +){ Sn IV Pc (3-) Cl 2}•- (1) was obtained by the reduction of tin(IV) phthalocyanine dichloride { Sn IV Pc (2-) Cl 2} with ( PPN +)( C 60•-) ( PPN + is bis(triphenylphosphoranylidene)-ammonium cation). It was shown that the reduction is centered mainly on the Pc ligand providing the appearance of a new band in the spectrum of 1 in the NIR range at 1006 nm and blue-shift of Soret and Q-bands of Sn IV Pc (2-) Cl 2. The alternation of short and long C – N imine bonds for two oppositely located isoindole units in 1 indicates possible disruption of aromaticity of the Pc ligand under reduction. Salt 1 has effective magnetic moment of 1.69 μB at 300 K corresponding to the contribution of one non-interacting S = 1/2 spin per formula unit and manifests antiferromagnetic coupling of spins with Weiss temperature of -7.3 K in the 400–30 K range. The salt shows a broad EPR signal with g = 1.9957 and linewidth of 19.3 mT at room temperature. The signal splits into two components below 120 K. Strong broadening of the EPR signal and shift of g-factors to smaller values in comparison with the EPR signal from radical anions of metal-free phthalocyanine { H 2 Pc (3-)}•- were attributed to the contribution of the { Sn III Pc (2-) Cl 2}- admixture with paramagnetic Sn III . There are π–π stacking one-dimensional chains composed of { Sn IV Pc (3-) Cl 2}•- in 1 along the a axis with weak overlapping between phenylene groups of phthalocyanine radical anions. The calculated HOMO–HOMO overlap integral is 0.0033 and the SOMO–SOMO overlap integral is only 0.0004. Metallic conductivity is not realized in 1 most probably due to weak SOMO–SOMO overlapping.

Synthesis, structures, and properties of crystalline salts with radical anions of metal-containing and metal-free phthalocyanines.

Radical anion salts of metal-containing and metal-free phthalocyanines [MPc(3-)](·-), where M = Cu(II), Ni(II), H2, Sn(II), Pb(II), Ti(IV)O, and V(IV)O (1-10) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C-Nimine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1-10 show new bands at 833-1041 nm in the NIR range, whereas the Q- and Soret bands are blue-shifted by 0.13-0.25 eV (38-92 nm) and 0.04-0.07 eV (4-13 nm), respectively. Radical anions with Ni(II), Sn(II), Pb(II), and Ti(IV)O have S = 1/2 spin state, whereas [Cu(II)Pc(3-)](·-) and [V(IV)OPc(3-)](·-) containing paramagnetic Cu(II) and V(IV)O have two S = 1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal-free phthalocyanine radical anions [H2Pc(3-)](·-) (linewidth of 0.08-0.24 mT), broad EPR signals are manifested (linewidth of 2-70 mT) with g-factors and linewidths that are strongly temperature-dependent. Salt 11 containing the [Na(I)Pc(2-)](-) anions as well as previously studied [Fe(I)Pc(2-)](-) and [Co(I)Pc(2-)](-) anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3-)](·-) in 1-10.

Design, crystal structures and magnetic properties of anionic salts containing fullerene C₆₀ and indium(III) bromide phthalocyanine radical anions.

Two salts containing fullerene C60 and indium(III) bromide phthalocyanine (Pc) radical anions have been obtained as single crystals: (TBA(+))3(C60˙(-)){In(III)(Br)(Pc)˙(-)}(Br(-))·C6H4Cl2 (1) and (TEA(+))2(C60˙(-)){In(III)(Br)(Pc)˙(-)}·C6H4Cl2·C6H14 (2) where TBA(+) and TEA(+) are tetrabutyl- and tetraethylammonium cations, respectively. The presence of both radical anions is supported by spectra of 1 and 2 in the NIR and IR-ranges. The salts contain zigzag C60˙(-) chains with 10.136 and 10.383 Å center-to-center (ctc) distances in 1 and a uniform ctc distance of 10.186 Å in 2. In 1, the C60˙(-) radical anions are dimerized in the 180-140 K range to form singly bonded (C60(-))2 dimers, whereas they remain monomeric in 2. Effective packing of planar In(Br)(Pc)˙(-) and spherical C60˙(-) is attained by introducing fullerene spheres between the phenylene substituents of Pc allowing the formation of multiple van der Waals contacts between them. The effective magnetic moment of 1 at 300 K is 2.35μ(B), indicating a contribution of both C60˙(-) and In(Br)(Pc)˙(-) species having S = 1/2 spin state. There is strong antiferromagnetic coupling of spins between fullerenes in the chains and fullerenes and phthalocyanines in the monomeric phase of 1 with the Weiss temperature of -120 K in the 300-180 K range. The formation of diamagnetic (C60(-))2 dimers switches off magnetic coupling and magnetically isolates In(Br)(Pc)˙(-) (Weiss temperature is only -1 K in the 140-10 K range). Magnetic behavior of 2 is described by the Curie-Weiss law with weak ferromagnetic coupling of spins with Θ = +7.6 K in the 50-300 K range. Both salts manifest single Lorentzian EPR lines at room temperature with g = 1.9911 and a linewidth (ΔH) of 25.4 mT (1) and g = 1.9956 and ΔH = 7.5 mT (2) which can be attributed to both C60˙(-) and In(Br)(Pc)˙(-) species having strong exchange interaction. An asymmetric signal with the main component at g = 1.989-1.965 in the dimeric phase of 1 was attributed to the In(Br)(Pc)˙(-) radical anions.

Identification of transient radical species in microbial systems using diffuse reflectance laser flash photolysisDedicated to Professor Frank Wilkinson on the occasion of his retirement.

Conventional and diffuse reflectance laser flash photolysis are used to study the disulfonated aluminium phthalocyanine radical anion (AlPcS2−˙), both in solution and in a microbial cell environment. The transient absorption of the AlPcS2−˙ is characterised using model quenchers and the bimolecular quenching rate constants (kQ) for several chemical components present in the outer membranes/cell structures of the microbes studied with AlPcS2 are determined. The generation of the AlPcS2−˙ by the microbial cells is investigated, and the relative quantum yields of this process are calculated, together with the transient lifetime of the AlPcS2−˙ in a microbial cellular environment. Supporting evidence is found for the involvement of type I processes in the overall photodynamic mechanism of AlPcS2 with the microbes studied. Several biological substrates present in the outer cell structures of the microbial cells studied are capable of quenching the AlPcS2 triplet state to generate the AlPcS2 radical anion (AlPcS2−˙), which is the reactive species that mediates type I photodynamic mechanisms. The transient absorption band of the AlPcS2−˙ is observed in the triplet minus singlet absorption spectra of AlPcS2 in the presence of each of the microbes.

Assignment of the optical spectrum of metal porphyrin and phthalocyanine radical anions

The approach developed previously to assign the major π → π* and π* → π* bands in the optical spectra of metallophthalocyanine radical species [ MPc (−n)](n−2)−(n = 1–6), which was based on spectral band deconvolution analyses of the UV-vis absorption and magnetic circular dichroism (MCD) spectra and ZINDO calculations, is reviewed in this paper and extended to the major bands observed in the spectrum of the zinc tetraphenylporphyrin radical anion [ ZnTPP (−3)]−. The magnetic circular dichroism spectrum is dominated by an intense pseudo A term associated with the B (or Soret) transition with bands at 445 and 465 nm. Weaker bands associated with the π* → π* transition out of the partially filled LUMO give rise to two widely separated, oppositely signed, coupled B terms in the MCD spectrum at 538 and 910 nm. The Q transition is assigned to a weak absorption band at 750 nm and a shoulder slightly to the blue at 728 nm.

Synthesis and characterization of new mixed-ligand lanthanide–phthalocyanine cation radical complexes

The mixed-ligand phthalocyanine lanthanide complexes [Ln(pc)X2] [pc = phthalocyanine radical anion; Ln = Sm, Eu, Gd or Lu; X = 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate (fod), 1,1,1-trifluoro-4-phenylbutane-2,4-dionate (btfa) or 3-heptafluorobutyryl-D-camphorate (hfbc)] have been synthesized and characterized by electronic, ESR and plasma desorption mass spectroscopy as well as elemental analysis. Bands in the electronic spectra at 820, 716, 500, 425 and 330 nm typical for phthalocyanine radical anions have been observed for the red initial [Ln(pc)X2] complexes. The ESR spectra are also consistent with the radical nature of the phthalocyanine ligand in these complexes. The reversible chemical reduction of [Ln(pc)X2] complexes has been studied.

Electrochromism in the transition-metal phthalocyanines. Part 3.—Molecular organisation, reorganisation and assembly under the influence of an applied electric field. Response of [Fe(pc)] and [Fe(pc)Cl

The electrochromic behaviour of α-[Fe(pc)] and [Fe(pc)Cl] has been studied, using cyclic voltammetry, electronic absorption spectroscopy and Mossbauer spectroscopy, the latter on 57Fe-enriched [Fe(pc)] films. [Fe(pc)] films have been shown to cycle reversibly ca. 103 times between neutral (blue) and reduced (purple-red) states (negative voltages), but decompose when oxidised repeatedly (positive voltages) in aqueous KCI electrolytes. When oxidised then reduced in < ca. 1 s [Fe(pc)Cl] is formed. This indicates that the Cl– ion adds as a ligand during the electrochromic oxidation and this takes place concomitantly with a lattice reorganisation. [Fe(pc)] films on oxidation produce red [FeIII(pc˙)Cl2] and contain a (pc˙) phthalocyanine radical anion. On reduction to neutral they become [Fe(pc)Cl].[Fe(PC)Cl] films have been shown to reduce electrochromically from an initial green film to a purple reduced film without first becoming [Fe(pc)]. However, on reoxidation to neutral, a blue [Fe(pc)] film is formed; this then behaves like a normal [Fe(pc)] film. These studies show that the axial Cl–on [Fe(pc)Cl], once removed, passes out of the lattice during the electrochromic reduction, and that under the influence of the field the lattice reorganises, assembling predominantly as the α-[Fe(pc)] phase.This is the first attempt to explain widespread lattice reorganisation that involves metallophthalocyanines with axial ligands attaching and detaching under controlled voltage.

Electronic spectra of phthalocyanine radical anions and cations

Abstract : The oxidation and reduction of metal phthalocyanines give rise to at least six oxidation states whose electronic spectra are rationalized in some depth in terms of SCF energies, Coulomb and exchange integrals. It is shown that a single set of parameters can reproduce the Q band energies moderately well. Further this same set of energies can reproduce differences in electrochemical potentials observed within this redox set. The pattern of variation in the Q band energies (and in their number) now provides a means for identifying whether it is the metal or the phthalocyanine ligand which is reduced upon addition of an electron to the system.