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We introduce some representative studies from our laboratory, mostly from the 21st Century. We are interested in the synthesis, optical spectroscopy, such as magnetic circular dichroism (MCD), circ...

A tribenzotetraazachlorin (TBTAC)-C(60) conjugate having three 15-crown-5 units as substituents, , has been synthesized, and the electronic and supramolecular structure modulations in the presence of Na(+) or K(+) have been elucidated by means of massmetric and spectroscopic techniques.

The synthesis, and spectroscopic and electrochemical properties of hydrogenated tetraazaporphyrins (TAPs), namely tetraazachlorins (TACs), tetraazabacteriochlorins (TABCs) and tetraazaisobacteriochlorins (TAiBCs), have been reviewed. While the first synthesis of this type of hydrogenated aromatic macrocycle was achieved as early as 1958 by Linstead et al. (G. E. Ficken, R. P. Linstead, E. Stephen and M. Whalley, J. Chem. Soc., 1958, 3879), the development of modern synthetic strategies enables us to isolate stable forms of the hydrogenated TAP derivatives. Benzo-, 2,3-naphtho- and 1,2-naphtho-fused derivatives were synthesized extensively, and all structural isomers have been elucidated. The chemical structures have been characterized using a variety of techniques, including mass spectrometry, 1H and 13C NMR, X-ray crystallography and IR spectroscopy. The spectroscopic properties (e.g., electronic absorption, magnetic circular dichroism (MCD), and fluorescence) of these compounds differ significantly from those of the original TAPs, or phthalocyanines (Pcs), due to the symmetry-lowering effects of the core aromatic macrocycles. The experimentally observed properties have been rationalized on the basis of electrochemical studies and quantum chemical calculations. As an application of the TAC skeleton, the synthesis and electronic structures of tribenzo TAC (TBTAC)-C60 conjugates, in which both components are covalently connected directly and thus show remarkable molecular orbital (MO) mixing between the constituting moieties, have also been reviewed.

Mixed condensation of 1,2-dicyanofullerene (1) and 4,5-dibutyloxyphthalonitrile (2a) in the presence of vanadium(III) chloride (VCl 3 ) in quinoline forms the hexabutyloxy-substituted tribenzotetraazachlorin (TBTAC) - fullerene (C 60 ) vanadyl complex (3). UV-vis absorption and magnetic circular dichroism (MCD) spectroscopy demonstrated that 3 shows two intense Q-band components, whereas the previously reported nickel complex possessing the identical peripheral substituents (4) shows one intense and two medium-intense bands in the 600-800 nm region, indicating that the electronic mixing states of 3 are different from those of the nickel complex (4). The metal effects on electronic structures of the conjugates were interpreted using density functional theory (DFT) calculations.

Novel tetraazachlorin (TAC)-fullerene (C60) conjugates (TAC-C60) and their analogues (TAiBC-C60 and TABC-C60 where TAiBC = tetraazaisobacteriochlorin and TABC = tetraazabacteriochlorin) have been synthesized by condensing 1,2-dicyanofullerene (1) and phthalonitrile derivatives (2) in the presence of nickel chloride in quinoline, and fully characterized using mass spectrometry and 1H and 13C NMR. By arranging the TAC and C60 units at the minimum distance, and taking also into account the molecular symmetry, the resultant conjugates show on-off electronic communication behavior, depending on the push-pull properties of the peripheral substituents in the TAC moiety. Consequently, the UV-vis absorption spectrum of the electron-releasing butyloxy-substituted TAC-C60 (3a) contains an unusual group of three absorption bands in the Q-band region (500-900 nm) as a result of a strong electronic communication between the two moieties. On the other hand, the absorption spectrum of the electron-withdrawing butylsulfonyl-substituted TAC-C60 (3b) comprises a typically normal TAC spectrum with markedly split two-peak Q-bands. A similar phenomenon is observed between alkoxy-substituted TAiBC-C60 (4a) and butylsulfonyl-substituted TAiBC-C60 (4b). This study reveals that the electron-donating or -withdrawing nature of the peripheral substituents on an azachlorin moiety has an important effect on the electronic structures of our novel azachlorin-C60 conjugates, although the linking carbon atoms are aliphatic sp3 carbon atoms which generally do not contribute to aromaticity. The electronic structures of the conjugates have been investigated in detail using spectroscopic and electrochemical techniques with the aid of DFT calculations.

cis-3,4-Dicyano-3-hexene undergoes cyclotrimerization with BCl3 to form the new subtriazaporphyrin chloro[hexaethylsubtriazaporphyrinato]boron(III). The hydroxo derivative of this macrocycle has also been made, and the X-ray crystal structure of the hydroxy form was determined. Electronic absorption and magnetic circular dichroism spectra of the hydroxo monomer species were interpreted using time-dependent density functional theory calculations.

Publisher Summary Phthalocyanine (Pc) was first synthesized in 1907, so the first centenary of Pc research is fast approaching. Because the heteroaromatic Pc ligand has a strong blue color and is chemically stable, Pc complexes have been used extensively in pigments and dyestuffs for more than 70 years. Pcs have also been used as catalysts for the removal of sulfur from crude oil; as charge-generation materials in xerography; in optical read/write discs; as photodynamic reagents for cancer therapy; in deodorants, germicides, and anti-bacterial reagents; and as growth promoting and retarding agents of plants. Other active fields of Pc-related research include applications in or as chemical sensors, electrochromism, conductors, semiconductors, and photovoltaic elements for electricity generation, one dimensional metals, non-linear optics, electrocatalysis, liquid crystals, Langmuir-Blodgett films, and electrophotography. Although most research results have been published as patents, academic research has become very intensive over the past 20 years.

The synthesis of a series of zinc phthalocyanines partially phenyl-substituted at the 1-, 4-, 8-, 11-, 15-, 18-, 22-, and/or 25-positions (the so-called alpha-positions) is reported. Macrocycle formation based on 3,6-diphenylphthalonitrile, o-phthalonitrile, and zinc acetate predominantly yielded the near-planar disubstituted complex and opposite tetrasubstituted isomer, while the lithium method yielded the sterically hindered hexasubstituted complex and adjacent tetrasubstituted isomer. All compounds have been characterized by 1H NMR, MALDI-TOF-MS, and elemental analysis methods. In addition, crystal structures have been solved for the di-, hexa-, and octasubstituted complexes and the adjacent tetrasubstituted isomer. DFT geometry optimization calculations predict more highly deformed structures than those observed in the crystals. The packing force of the crystals cannot therefore be ignored, particularly for the less phenyl-substituted derivatives. The crystal structures have revealed that overlap of the phenyl groups causes substantial deformation of the phthalocyanine (Pc) ligands within the crystals, while strong pi-pi stacking in the remainder of the Pc moiety lacking phenyl substituents can suppress the impact of the deformation. Absorption spectra show sizable red shifts of the Q-band with increasing number of phenyl groups. Analysis of the results of absorption spectra and electrochemical measurements reveals that a substantial portion of the red shift is attributable to the ring deformations. Molecular orbital calculations lend further support to this conclusion. A moderately intense absorption band emerging at around 430 nm for highly deformed octaphenyl-substituted zinc Pc can be assigned to the HOMO-->LUMO+3 transition, which is parity-forbidden for planar Pcs, but becomes allowed since the ring deformations remove the center of symmetry.

Two novel homoleptic diazaporphyrinato lanthanide sandwich com-plexes M(2)(DAP)(3) [M = Ce (1), Eu (2); DAP= 2,8,12,18-tetra-ethyl-3,7,13,17-tetramethyl-5,15-diazaporphyrinate] were synthesized by a one-pot reaction of the corresponding M(acac)(3).nH(2)O (acac = acetylacetonate) with metal-free D(2)(h) type diazaporphyrin, H(2)DAP. The spectroscopic and electrochemical properties are compared with those of complexes based on D(4)(h) symmetry porphyrin ligands.

Tetraazaporphyrins (TAPs), phthalocyanines (Pcs), naphthalocyanines (Ncs), and anthracocyanines (Acs) with four tert-butyl groups attached at similar positions have been synthesized, and their electronic absorption, magnetic circular dichroism (MCD), IR, and voltammetric properties were studied and interpreted with the help of quantum-mechanical calculations. Through the preparation of a series of compounds with the same number of the same substituent, the effects of the increase in the size of the ring system were clearly derived. The main results may be summarized as follows. 1) The Q band shifts to longer wavelength and its intensity increases, but with decreasing degree of change with increasing molecular size. If the size of the effect of benzene directly fused to the TAP skeleton is set at unity, the effects of the second and third benzene units are roughly 0.8 and 0.5, respectively. 2) The splitting of the Q bands in metal-free compounds decreases with increasing molecular size, so that the Q bands of H2Nc and H2Ac appear as single bands. 3) The magnitude of the orbital angular momentum of the excited state of the ligand decreases with increasing molecular size. 4) Interestingly, the ring current, as judged from the positions of pyrrole proton signals in the 1H NMR spectrum, appears to decrease with increasing molecular size. 5) The first reduction potential becomes less negative, but only slightly, whereas the first oxidation potential shows a marked shift to less positive values with increasing molecular size, indicating that the HOMO destabilizes significantly as the molecule becomes larger. 6) In 5), the extent of the HOMO destabilization with molecular size differs depending on the central metal, so metals producing smaller destabilization effects can allow larger macrocycles. Of the metals studied, the most effective is cobalt, and the practical size limit is represented by the Acs. 7) The IR spectra become simpler the larger the molecule, and the main bands were assigned by DFT calculations. 8) The trend in experimentally determined redox potentials and electronic absorption and MCD spectra were reasonably reproduced by MO calculations using the ZINDO/S Hamiltonian. 9) EPR data for several metallocomplexes are also reported.

A method which preferentially produces adjacently di-aromatic ring-substituted tetraazaporphyrins (TAPs) has been developed, and their electrochemical and spectroscopic properties have been studied and compared with those of the corresponding series of mono-aromatic ring-fused TAPs. Mono-aromatic ring-fused TAPs show a split Q-band, and the splitting energy increases with increasing size of the aromatic ring. In addition, for the split Q-bands, the relative intensity of the band at longer wavelength decreases with increasing molecular size of the fused aromatics, compared with the shorter wavelength band. In the di-aromatic ring-fused TAPs, this kind of splitting is not seen, and only a shift of the band is observed. The intensity and band position of the split or unsplit Q-bands are quantitatively evaluated by simultaneous band deconvolution analysis, using both electronic absorption and magnetic circular dichroism spectra. The preparation of these TAP compounds has made it possible to adjust the Q-band position in a stepwise manner between ca. 600 and 750 nm. The first reduction and oxidation potentials of the TAP ring shift negatively with increasing number and size of the fused aromatics. The extent of the shift is found to be very small for the LUMOs but significant for the HOMOs. These spectroscopic and electrochemical properties are almost perfectly reproduced by molecular orbital calculations within the framework of the Pariser-Parr-Pople approximation. In particular, a small variation of the LUMO level and large destabilization of the HOMO level on ring expansion are rationalized from the extent of stretch of molecular orbitals: i.e., since the LUMOs are localized in the central TAP moiety irrespective of the molecular size, while the HOMOs have appreciable coefficients even over the fused aromatics, the HOMO level destabilizes while the LUMO level remains constant with increasing molecular size. In one CoTAP derivative, Co(III/II) and the first ligand oxidation couples occur experimentally at the same potential.

The electronic absorption and magnetic circular dichroism spectral data of a phthalocyanine dicopper complex that is deduced to be very planar and to share a common benzene ring have been studied by band deconvolution analysis. The results were compared with those of the molecular orbital (MO) calculations within the framework of the Pariser−Parr−Pople (PPP) approximation. The results of the band deconvolution analysis are in good agreement with those of the PPP calculations, allowing many bands to be reasonably assigned on the basis of the MO calculations. The validity of the PPP method for the MO calculation of large molecules is also emphasized.

The reaction of a double-decker phthalocyanine (Pc) complex, bis(phthalocyaninato)lutetium ([LuPc(2)](-)), with cadmium acetate at 400 degrees C for 30 min under argon provided the first example of a discrete quadruple-decker Pc complex, 1. The structure of 1 was unambiguously determined through the use of high-resolution mass spectrometry, elemental analysis, and NMR techniques such as (1)H-(1)H COSY, (13)C-(1)H COSY, and NOE experiments. The absorption and magnetic circular dichroism spectra of 1 resembled those of [LuPc(2)](-) and [Lu(2)Pc(3)] rather than those of the neutral double-decker species [LuPc(2)](0), since the formal charge on each Pc moiety is 2-. Electrochemical measurements exhibited a stacking effect based on the delocalization of the holes or electrons introduced by oxidation or reduction, respectively, over the entire complex.

The crystal structure of 5,10,15,20-tetramethyl-21H,23H-porphine vanadium(IV) oxide, VO(TMP), has been determined. Monoclinic, P21/a, a = 14.298(5), b = 13.445(4), c = 19.895(6)A, β = 97.487(2). Z = 8, C24H20N4OV.

A novel μ-oxo hetero dimer of silicon phthalocyanine and silicon naphthalocyanine was synthesized. Its unique optical properties, such as a single Q band, which is unusual for hetero dimer species, and solvatochromic behavior, were revealed to be better interpreted by taking interchromophore interactions into consideration.

A reaction of 1,2-dicyanobenzene and lithium methoxide at 70 °C in methanol yielded the half-phthalocyanine intermediate, which coordinates to a cadmium(II) ion in the subsequent reaction step to give the first example of a six-coordinate phthalocyanine analogue containing a divalent metal ion at the center.

Vibrational circular dichroism (VCD) spectra of (R)-(−)- and (S)-(+)-camphor-substituted tetrapyrazinoporphyrazines, which show a mirror-image relationship with respect to the line of intensity = 0...

Metal complexes of a highly deformed 1,4,8,11,15,18,22,25-octaphenylphthalocyanine have been synthesized, and found to show various colors ranging from bright green, ocher, and red depending on the central metal employed.

Two terbium ions in a triple-decker complex (Pc)Tb(Pc)Tb(T(p-OMe)PP) (Pc = phthalocyaninato, T(p-OMe)PP = tetra-p-methoxyphenylporphyrinato) have shown sharply different magnetic behaviours depending on symmetry of the coordination polyhedron. The fast quantum tunnelling relaxation process in a square-prismatic site has been revealed to be hindered by magnetic-dipolar coupling between the f-electronic systems.

Homo and heteronuclear quadruple-decker phthalocyanine tetramers containing Y(3+) and/or magnetically anisotropic lanthanide ions such as Tb(3+), Dy(3+), and Er(3+) have been synthesized, and their magnetic properties have been elucidated, giving clear evidence of the long-range interactions between two f-electronic centers.

The C2v isomer of Co(1,2-Nc-C2v) (1,2-Nc = 1,2-naphthalocyaninato) has been isolated by fractional crystallization of the crude mixture of four isomers (C4h, Cs, C2v, D2h), and its crystal structure, electronic absorption, and magnetic circular dichromism have been discussed.

A novel platinum-based macrocycle, iron(II) tetrakis(diaquaplatinum)octacarboxyphthalocyanine (PtFeOCPc), was synthesised and characterised. The heterogeneous electron transfer and electrocatalytic properties of this functional material towards the oxidation of formic acid have been explored on a graphite electrode platform pre-modified with or without acid-functionalised multi-walled carbon nanotubes (MWCNTs). We prove that PtFeOCPc supported on a MWCNT platform (MWCNT–PtFeOCPc) exhibits enhanced electrochemical response in terms of (i) electron transfer towards outer-sphere redox probe, (ii) catalytic rate constant, and (iii) tolerance towards CO poisoning during formic acid oxidation. The results clearly suggest that the MWCNT–PtFeOCPc is a promising platform for potential application as an electrocatalyst for direct formic acid fuel cell.

Electroabsorption spectra of electron donating butyloxy- (OBu) or electron withdrawing butylsulfonyl (SO(2)Bu)-substituted tribenzotetraazachlorin (TBTAC)-C(60) conjugates (1 and 2, respectively) have demonstrated that significant change of the molecular polarizability is associated with the photoexcitation of 1 in the lower energy region, while that in the higher energy region is comparable with the corresponding band of 2, although the pi-aromatic structures of 1 and 2 are identical to each other, being consistent with the previously reported result of the DFT calculations.

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A subphthalocyanine (SubPc) dimer linked by racemic 1,1'-binaphth-2,2'-dioxy (BINOL), 1, has been synthesized and characterized by 1- and 2-D 1H NMR, high resolution mass spectrometry (FAB), X-ray crystallography and electronic absorption spectroscopy. Additionally, the dimer derived from optically-active (R)-(+)-BINOL, 2, has been made and studied using CD and MCD spectroscopies.

A highly deformed [1,4,8,11,15,18,22,25-octaphenylphthalo-cyaninato(2-)]iron(II) has been synthesized, and found to show absorption bands which may be assigned to metal-to-ligand charge transfer (MLCT) transitions in the near-IR region beyond the Q-band in pyridine, due to lowering of molecular symmetry to D2d from D4h symmetry of normal metallophthalocyanines.