Hiroaki Isago

Synthesis and properties of a highly soluble dihydoxo(tetra-tert-butylphthalocyaninato)antimony(V) complex as a precursor toward water-soluble phthalocyanines

The title complex cation, [Sb(tbpc)(OH)(2)](+) (where tbpc denotes tetra(tert-butyl)phthalocyaninate, C(48)H(48)N(8)(2-)), has been prepared by oxidizing [Sb(tbpc)]I(3) with tert-butyl perbenzoate in CH(2)Cl(2), CHCl(3), o-dichlorobenzene and also without solvent in the range of 20-80 degrees C. This species has been isolated as I(3)(-) salt and characterized by elemental analysis, ESI-MS, FT-IR, optical absorption and emission, and magnetic circular dichroism spectroscopy. This compound is quite well soluble in common polar organic solvents (e.g., CH(2)Cl(2), acetonitrile, acetone) without detectable aggregation at least up to ca. 10(-4)M while much less soluble (e.g., benzene, chloronaphthalene) or insoluble (hexane) in non-polar solvents. Although this compound is insoluble in water, it makes hydrophilic colloids in acetone-water mixtures. The most intense absorption band (Q-band) in a specific solvent red-shifts with an increase in the refractive index of the solvent. However, considerable deviation of the Q-band positions in donor-solvents from linear correlation between the positions and Onsagers solvent polarity function suggests that there are significant specific chemical interactions between the axial hydroxyl groups and the surrounding donor molecules. The low fluorescence quantum yield (ca. 0.01) for [Sb(tbpc)(OH)(2)](+) suggests that the singlet excited state of this species is considerably quenched by the presence of antimony ion in the chromophore.

The syntheses of amphiphilic antimony(V)-phthalocyanines and spectral investigation on their aggregation behaviors in aqueous and non-aqueous solutions.

Three amphiphilic antimony(V)-phthalocyanines have been synthesized by treating [Sb(R(4)Pc)(OH)(2)](+) salts in concentrated H(2)SO(4) and isolated as zwitter ions, [Sb(R(4)Pc)(SO(4)H)(SO(4))], where R(4)Pc denotes tetra-substituted phthalocyaninate; R(4)Pc=pc (R=H), tbpc (R=(t)Bu), and tObpc (R=O(n)Bu). Their solubility (R=tbpc>pc >>tObpc in H(2)O (much improved by the presence of surfactant or alcohol) while tbpc>tObpc >>pc in CH(2)Cl(2)) and aggregation behaviors are highly sensitive to the nature of the peripheral substituents. The pc and tbpc derivatives form well-behaved J-aggregates in aqueous media in the presence of surfactant or alcohol.

The synthesis and spectral investigation of a novel highly water-soluble, aggregation-free antimony(V)-phthalocyanine absorbing light in optical therapeutical window

A novel antimony-phthalocyanine, [Sb(H(3)tsppc)(OH)(2)], where H(3)tsppc denotes monodeprotonated tetrakis{(2,6-dimethyl-4-sulfonic acid)phenoxyl}phthalocyaninate, has been synthesized through sulfonation of [Sb(tppc)(OH)(2)](+) (tppc denotes tetrakis{(2,6-dimethyl)phenoxyl}phthalocyaninate) in concentrated sulfuric acid. This compound is highly soluble in water (ca. 4 × 10(-2) M) without surfactant or alcohol. Moreover, it has been found free from aggregation in water up to almost 10(-4) M, unlike its copper and metal-free analogues, and show an intense optical absorption and emission band in optical therapeutical window (700-800 nm). The axial hydroxyl groups play a crucial role in disaggregation of the antimony derivative in water.

Spectral properties of a novel antimony(III)-phthalocyanine complex that behaves like J-aggregates in non-aqueous media

An unusual red-shift of phthalocyanine Q-band upon aggregation in non-aqueous media has been observed for antimony(III) derivative and has been studied by using optical absorption and magnetic circular dichroism spectroscopy.

A new spectroelectrochemical cell with a long optical path length for redox studies of phthalocyanines

A new spectroelectrochemical cell with a long optical path length has been fabricated for redox studies of phthalocyanines, where the propagation axis of the optical beam is parallel to the electrode/solution interface. It is composed of a homemade Teflon block that fits inside a standard 1 cm quartz optical-cell, equipped with a platinum-foil working electrode, a platinum-wire auxiliary electrode, and a AgCl-coated silver-wire reference electrode. This new cell makes it much easier to acquire spectral data for dilute solutions containing species, like phthalocyanines, that have limited solubility in common organic solvents or that strongly aggregate in solution. As examples, electrolyses of the [tetra(tert-butyl)phthalocyaninato]zinc(II) complex and its cobalt(II) analogue were performed to monitor spectral changes ascribable to phthalocyanine-ligand-centered oxidation and metal-centered reduction, respectively. Spectra of unaggregated electrogenerated species were successfully observed.

Optical Emission Spectra of Phthalocyanines

In this chapter, optical emission phenomena involving phthalocyanine derivatives and the related macrocyclic compounds are described. In particular, we focus on the fluorescence emitted from the macrocyclic ligand with a brief discussion of other emission phenomena (e.g., phosphorescence, delayed fluorescence, electro-chemiluminescence). Unlike optical absorption, not all macrocyclic compounds luminesce. In this chapter, the factors that cause macrocyclic dyes to be luminescent or nonluninescent are described. Furthermore, we focus on the aggregation and acid-base equilibrium involving these compounds in detail because these phenomena are frequently misunderstood.

Valence States of Rare-Earth Ions and Band Gaps in RBiBa2O6 (R = La, Ce, Pr, Nd, Sm, Gd, Eu, and Dy) Photocatalysts

We have measured magnetic susceptibility, powder X-ray diffraction (XRD), and diffuse reflectance spectra of RBiBa2O6 (R = La, Ce, Pr, Nd, Sm, Gd, Eu, and Dy). The valences of the rare earth elements estimated from magnetic susceptibility were trivalent except CeBiBa2O6 and PrBiBa2O6 in which Ce and Pr were tetravalent. In PrBiBa2O6, a significant effect of crystal fields on magnetic susceptibility was observed below 200 K. The (111) reflection in XRD, which is evidence for the R3+–O–Bi5+ ordering in the double-perovskite structure, was observed in all samples except CeBiBa2O6. In PrBiBa2O6, a weak (111) reflection was observed suggesting that a small amount of Pr3+ ions were present. The band gaps estimated from their optical spectra were approximately 0.7 eV for CeBiBa2O6, 1.1 eV for PrBiBa2O6, and 1.4–1.7 eV for R3+BiBa2O6. Thus the band-gaps were closely related to the valences of RBiBa2O6. We discuss the relationship between these physical properties and the photocatalytic activities previously reported.

Solvent effects on molecular aggregation of highly water-soluble phthalocyanines

Molecular aggregation phenomena of a highly water-soluble, metal-free phthalocyanine, H2Pc, and its copper complex, Cu(Pc); where Pc denotes tetrakis{(2′,6′-dimethyl-4′-sulfonic acid)phenoxy}phthalocyaninate) in water, ethanol, and their mixed solvent systems have been investigated by spectroscopic approach In both aqueous and ethanolic solutions, H2Pc molecules aggregate in a slipped-cofacial manner, although very weakly in ethanol. On the other hand, Cu(Pc) molecules aggregate in a cofacial manner in water while aligning in a slipped-cofacial manner in ethanol. Magnetic circular dichroism spectroscopy was undertaken to investigate aggregation behaviors of Cu(Pc) in water and ethanol. Presence of 4-phenylpyridine in ethanol effectively inhibited aggregation of Cu(Pc) molecules, although little affected the spectra of the monomers. In a mixed solvent system, where water/ethanol = 10/90 (v/v), Cu(Pc) is free from aggregation up to almost 10-4 M. Driving forces of this molecular aggregation are discussed on...

Real Optical Absorption Spectra Observed in Laboratories

In this chapter, some factors that internally and externally affect the optical absorption spectra of phthalocyanine derivatives and related macrocyclic compounds are described and it is illustrated how they contribute to the deviation from the prototypical spectrum. The internal factors include the type and position of substituent(s) on the periphery of the macrocycle, the expansion of the π-conjugation system, the nature of the metal ion in the cavity of the macrocycle (ion size, oxidation number, and coordination geometry), and that of the axial ligand on the central metal ion. The external factors cover acid-base equilibrium, oxidation and reduction on the macrocycle, aggregation and dimerization (exciton coupling and π–π interaction), and solvent effects. In particular, much attention is focused on aggregation and acid-base equilibrium because these phenomena are frequently misunderstood.

Amphoteric phosphorous(V)-phthalocyanines as proton-driven switchable fluorescers toward deep-tissue bio-imaging

Spectral (optical absorption and emission) properties of three amphoteric phosphorous(V)-phthalocyanine derivatives, [P(Pc)(O)OH], where Pc=tetra(tert-butyl)phthalocyaninate (tbpc), tetrakis(2,6-dimethylphenoxy)phthalocyaninate (tppc), and octakis(4-tert-butylphenoxy)phthalocyaninate (obppc), have been investigated in ethanolic solutions. Spectral changes upon protonation/deprotonation (the reaction sites have been determined to be their axial ligands by magnetic circular dichroism study) are drastic and rapid. All the initial ([P(Pc)(O)OH]), protonated ([P(Pc)(OH)2]+), and deprotonated ([P(Pc)(O)2]-) species are possessed with sufficient brightness (defined as the product of their molar extinction coefficient, ε (inM-1cm-1), and fluorescence quantum yield, ΦF) in bio-imaging window (650-900nm). For example, spectral characteristics of the tbpc derivatives have been determined as follows: ε=1.65×105 (absorption maximum 676nm) and ΦF=0.80 (emission maximum 686nm) for [P(tbpc)(O)(OH)] while ε=1.45×105 (697nm) and ΦF=0.27 (714nm) for [P(tbpc)(OH)2]+, and ε=2.25×105 (662nm) and ΦF=0.90 (667nm) for [P(tbpc)(O)2]-. Emission of tppc and obppc derivatives behave in essentially the same manner irrespective of nature of the peripheral substituents and hence ΦF values are greater with increasing emission peak wavenumbers in line with the energy gap law. These characteristics make these compounds promising candidates as chemical probes for deep-tissue bio-imaging.