Taniyuki Furuyama

Rationally designed phthalocyanines having their main absorption band beyond 1000 nm.

Highly air-stable phthalocyanines (Pcs) having their main absorption band beyond 1000 nm have been synthesized using main-group elements as peripheral and central (core) substituents. The resultant [(PhS)(8)PcP(OMe)(2)][PF(6)] and [(PhSe)(8)PcP(OMe)(2)][PF(6)] show a single Q-band peak at 1018 and 1033 nm, respectively, which was achieved by carefully taking into account the spectroscopic properties of Pcs and the characteristics of the frontier orbitals. The large red shift can be considered to originate from synergistic effects involving both the group-15 and -16 elements.

Design, Synthesis, and Properties of Phthalocyanine Complexes with Main-Group Elements Showing Main Absorption and Fluorescence beyond 1000 nm

We present a comprehensive description of the unique properties of newly developed phthalocyanines (Pcs) containing main-group elements that absorb and emit in the near-IR region. Group 16 (S, Se, and Te) elements and group 15 (P, As, and Sb) elements were used as peripheral and central (core) substituents. With the introduction of group 16 elements into free-base Pc, a red-shift of the Q-band was observed, as a result of the electron-donating ability of group 16 elements particularly at the α positions. An X-ray crystallographic analysis of α-ArS-, ArSe-, and ArTe-linked free-base Pcs was also successfully performed, and the relationship between structure and optical properties was clarified. When a group 15 element ion was introduced into the center of the Pc ring, the resulting Pcs showed a single Q-band peak beyond 1000 nm (up to 1056 nm in CH2Cl2). In particular, [(ArS)8PcP(OMe)2](+) and [(ArS)8PcAs(OMe)2](+) exhibited a distinct fluorescence in the 960-1400 nm region with moderate quantum yields. The atomic radius of the group 15 element is important for determining the Pc structure, so that this can be controlled by the choice of group 15 elements. Electrochemical data revealed, while MO calculations suggested, that the red-shift of the Q-band is attributable to a decrease of the HOMO-LUMO gap due to significant and moderate stabilization of the LUMO and HOMO, respectively. The effect of peripheral substutuents and a central P(V) ion on the Q-band shift was independently predicted by MO calculations, while the magnitude of the total calculated shift was in good agreement with the experimental observations. The combination of spectral, electrochemical, and theoretical considerations revealed that all of the central group 15 elements, peripheral group 16 elements, and their positions are necessary to shift the Q-band beyond 1000 nm, indicating that the substitution effects of group 15 and 16 elements act synergistically. The Pcs having Q-bands beyond 1000 nm in this study also had stability under aerobic conditions comparative to that of CuPc, which is presently being widely used in consumer products.

Development of Mono- and Di-AcO Substituted BODIPYs on the Boron Center

Mono- and di-AcO substituted BODIPYs (1 and 2) were synthesized from TM-BDP. The structures of 1 and 2 were supported by single crystal X-ray analysis. Both 1 and 2 possess a large absorption coefficient, high fluorescence quantum yield, and high light stability. Compound 2 has much improved water solubility which is highly desirable for biological applications. Theoretical calculation supports our observations in X-ray analysis, absorption, and cyclic voltammetry.

Absorption and electrochemical properties of cobalt and iron phthalocyanines and their quaternized derivatives: aggregation equilibrium and oxygen reduction electrocatalysis.

The synthesis and investigation of the electronic properties of Co(II) and Fe(II)tetrakis(pyridine-3-yloxy)phthalocyanines, as well as the respective quaternized complexes, are reported here. After quaternization reaction, the compounds showed increased solubility in water, and their aggregation equilibrium was analyzed by varying the solution concentration, pH, and composition. Cyclic voltammograms of the four compounds showed both metal and ring centered redox processes, with the former being highly sensitive to methylation of the pyridyl groups. The catalytic effect of the phthalocyanines adsorbed on glassy carbon electrodes in the oxygen reduction reaction (ORR) was investigated by cyclic voltammetry (CV) and rotating disk voltammetry (RDV). The highest catalytic activities were observed for the Fe(II) complexes in alkaline media, and a 2 + 2 mechanism, which consists of a first complete O2 to H2O2 process and a subsequent incomplete H2O2 to H2O process, is proposed.

Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] π‐Electron Systems

The electronic excited states of two forms of meso-hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1) have been investigated by density functional calculations and magnetic circular dichroism (MCD) spectroscopy, in order to assign their low-energy excited singlet states. We found that the perimeter model can be successfully applied to the interpretation of the electronic states. In the case of the neutral forms (Au(2)-N, Au-N), the absorption bands observed in the NIR and visible region can be assigned to pi-pi* transitions referred to as the L and B bands, respectively, analogous to the Q and Soret bands of regular porphyrins. In marked contrast with the neutral forms, the absorption bands of the reduced forms (Au(2)-R and Au-R) are attributed to pi-pi* transitions involving six frontier molecular pi orbitals. By applying the 4N-electron perimeter model, the six orbitals are labeled as h(-), h(+), s(-), s(+), l(-), and l(+), while the observed absorption bands can be assigned to the S, N(1), N(2), P(1), and P(2) transitions, in order of increasing energy.

An Extremely Air-Stable 19π Porphyrinoid

A one-electron reduced species of a cationic phosphorus(V) tetraazaporphyrin complex has been isolated as an air-stable solid. Cyclic voltammetry and magnetic measurements showed the species to be a neutral π radical, and the solid state structure was elucidated by single crystal X-ray diffraction analysis. Magnetic circular dichroism spectroscopy and theoretical calculations also support a 19π electron conjugated electronic circuit.

Enantioselective Diels–Alder Reaction of 1,2-Dihydropyridines with Aldehydes Using β-Amino Alcohol Organocatalyst

The enantioselective Diels-Alder reaction of 1,2-dihydropyridines with aldehydes using an easily prepared optically active β-amino alcohol catalyst was found to provide optically active isoquinuclidines, an efficient synthetic intermediate of pharmaceutically important compounds such as oseltamivir phosphate, with a satisfactory chemical yield and enantioselectivity (up to 96%, up to 98% ee). In addition, the obtained highly optically pure isoquinuclidine was easily converted to an optically active piperidine having four successive carbon centers.

Superazaporphyrins: Meso‐Pentaazapentaphyrins and One of Their Low‐Symmetry Derivatives

Supersized: Three pentaazapentaphyrin derivatives, that is, the superazaporphyrins (SAzPs), as well as a superphthalocyanine (SPc) and a mixed low-symmetry derivative have been prepared and characterized. Decaaryl SAzPs have a distorted (4n+2) π structure and show the Q bands at about λ=840-880 nm. These compounds are relatively air stable.

Synthesis of new chlorin e6 trimethyl and protoporphyrin IX dimethyl ester derivatives and their photophysical and electrochemical characterizations.

In view of increasing demands for efficient photosensitizers for photodynamic therapy (PDT), we herein report the synthesis and photophysical characterizations of new chlorin e6 trimethyl ester and protoporphyrin IX dimethyl ester dyads as free bases and Zn(II) complexes. The synthesis of these molecules linked at the β-pyrrolic positions to pyrano[3,2-c]coumarin, pyrano[3,2-c]quinolinone, and pyrano[3,2-c]naphthoquinone moieties was performed by using the domino Knoevenagel hetero Diels-Alder reaction. The α-methylenechromanes, α-methylenequinoline, and ortho-quinone methides were generated in situ from a Knoevenagel reaction of 4-hydroxycoumarin, 4-hydroxy-6-methylcoumarin, 4-hydroxy-N-methylquinolinone, and 2-hydroxy-1,4-naphthoquinone, respectively, with paraformaldehyde in dioxane. All the dyads as free bases and as Zn(II) complexes were obtained in high yields. All new compounds were fully characterized by 1D and 2D NMR techniques, UV/Vis spectroscopy, and HRMS. Their photophysical properties were evaluated by measuring the fluorescence quantum yield, the singlet oxygen quantum yield by luminescence detection, and also the triplet lifetimes were correlated by flash photolysis and intersystem crossing (ISC) rates. The fluorescence lifetimes were measured by a time-correlated single photon count (TCSPC) method, fluorescence decay associated spectra (FDAS), and anisotropy measurements. Magnetic circular dichroism (MCD) and circular dichroism (CD) spectra were recorded for one Zn(II) complex in order to obtain information, respectively, on the electronic and conformational states, and interpretation of these spectra was enhanced by molecular orbital (MO) calculations. Electrochemical studies of the Zn(II) complexes were also carried out to gain insights into their behavior for such applications.

A Bottom-up Synthesis of Antiaromatic Expanded Phthalocyanines: Pentabenzotriazasmaragdyrins, i.e. Norcorroles of Superphthalocyanines.

The first example of an antiaromatic expanded phthalocyanine, classified as a norcorrole of a superphthalocyanine has been prepared and fully characterized. The newly developed phthalonitrile dimerization reaction was a crucial step, which allowed for the bottom-up synthesis of expanded phthalocyanines. Their structure was confirmed by single crystal X-ray diffraction analysis. The 20 π antiaromaticity of the macrocycles was suggested by optical and theoretical calculations.