Proton-coupled electron-transfer reduction of dioxygen catalyzed by a saddle-distorted cobalt phthalocyanine.

Proton-coupled electron-transfer reduction of dioxygen (O(2)) to afford hydrogen peroxide (H(2)O(2)) was investigated by using ferrocene derivatives as reductants and saddle-distorted (α-octaphenylphthalocyaninato)cobalt(II) (Co(II)(Ph(8)Pc)) as a catalyst under acidic conditions. The selective two-electron reduction of O(2) by dimethylferrocene (Me(2)Fc) and decamethylferrocene (Me(10)Fc) occurs to yield H(2)O(2) and the corresponding ferrocenium ions (Me(2)Fc(+) and Me(10)Fc(+), respectively). Mechanisms of the catalytic reduction of O(2) are discussed on the basis of detailed kinetics studies on the overall catalytic reactions as well as on each redox reaction in the catalytic cycle. The active species to react with O(2) in the catalytic reaction is switched from Co(II)(Ph(8)Pc) to protonated Co(I)(Ph(8)PcH), depending on the reducing ability of ferrocene derivatives employed. The protonation of Co(II)(Ph(8)Pc) inhibits the direct reduction of O(2); however, the proton-coupled electron transfer from Me(10)Fc to Co(II)(Ph(8)Pc) and the protonated [Co(II)(Ph(8)PcH)](+) occurs to produce Co(I)(Ph(8)PcH) and [Co(I)(Ph(8)PcH(2))](+), respectively, which react immediately with O(2). The rate-determining step is a proton-coupled electron-transfer reduction of O(2) by Co(II)(Ph(8)Pc) in the Co(II)(Ph(8)Pc)-catalyzed cycle with Me(2)Fc, whereas it is changed to the electron-transfer reduction of [Co(II)(Ph(8)PcH)](+) by Me(10)Fc in the Co(I)(Ph(8)PcH)-catalyzed cycle with Me(10)Fc. A single crystal of monoprotonated [Co(III)(Ph(8)Pc)](+), [Co(III)Cl(2)(Ph(8)PcH)], produced by the proton-coupled electron-transfer reduction of O(2) by Co(II)(Ph(8)Pc) with HCl, was obtained, and the crystal structure was determined in comparison with that of Co(II)(Ph(8)Pc).

Relationship between crystal packing and high electron mobility in the single crystal of thienyl-substituted methanofullerene.

The X-ray crystal structure of 1-(3-methoxy-carbonyl)-propyl-1-thienyl-[6,6]-methanofullerene (ThCBM) was determined and the electron mobility of the single crystal was measured using a TRMC method to reveal high electron mobility (2 cm(2) V(-1) s(-1)) along the long axis (a-axis) and its remarkable anisotropy (7 times).

Control of electron-transfer reduction by protonation of zinc octabutoxyphthalocyanine assisted by intramolecular hydrogen bonding.

Facile protonation of α-octabutoxyphthalocyaninato zinc(II) (Zn(OBu)(8)Pc) occurs to afford up to tetra-protonated species stabilized by intramolecular hydrogen bonding, resulting in positive shifts of the reduction potentials of Zn(OBu)(8)PcH(n)(n+) (n = 1-4) with increasing the number of protons attached to facilitate electron-transfer reduction.

Structure and photoinduced electron transfer dynamics of a series of hydrogen-bonded supramolecular complexes composed of electron donors and a saddle-distorted diprotonated porphyrin.

The excited-state photodynamics of intrasupramolecular photoinduced electron transfer was investigated in a series of hydrogen-bonded supramolecular complexes composed of diprotonated 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H(4)DPP(2+)) and electron donors bearing a carboxylate group. The formation of supramolecular complexes was examined by spectroscopic measurements. The binding constants obtained by spectroscopic titration indicate the strong binding (10(8)-10(10) M(-2)) even in a polar and coordinating solvent, benzonitrile (PhCN). The crystal structure of the supramolecular assembly using ferrocenecarboxylate (FcCOO(-)) was determined to reveal a new structural motif involving two-point and single-point hydrogen bonding among saddle-distorted H(4)DPP(2+) dication and two FcCOO(-) anions. Femtosecond laser flash photolysis was applied to investigate the photodynamics in the hydrogen-bonded supramolecular complexes. Rate constants obtained were evaluated in light of the Marcus theory of electron transfer, allowing us to determine the reorganization energy and the electronic coupling matrix constant of photoinduced electron transfer and back electron transfer to be 0.68 eV and 43 cm(-1), respectively. The distance dependence of electron transfer was also examined by using a series of ferrocenecarboxylate derivatives connected by linear phenylene linkers, and the distance dependence of the rate constant of electron transfer (k(ET)) was determined to be k(ET) = k(0) exp(-beta r), in which beta = 0.64 A(-1).

Crystal structures and properties of a monoprotonated porphyrin.

A stable monoprotonated porphyrin (porphyrin monoacid) was obtained by reaction of saddle-distorted dodecaphenylporphyrin with anthracene sulfonic acids and the crystal structures of the supramolecular assemblies were determined.

Charge separation in metallomacrocycle complexes linked with electron acceptors by axial coordination.

A simple but elegant way to obtain linked donor-acceptor entities involving metallomacrocycle complexes with fixed distance and orientation is the use of coordination of axial ligands to metallomacrocycle complexes. A series of electron acceptor-bearing silicon phthalocyanine (SiPc) triads have been readily synthesized, using the six-coordinated nature of the central silicon atom, by attachment of two electron-acceptor units, fullerene SiPc-(C(60))(2), trinitrofluorenone SiPc-(TNF)(2) and trinitrodicyanomethylenefluorene SiPc-(TNDCF)(2). The nitrogen of pyridylnaphthalenediimide (PyNIm) can coordinate to the metal center of zinc porphyrin to form a donor-acceptor complexes: ZnTPP-PyNIm. The binding of pyridine moieties to Zn-porphyrin complexes is much enhanced by the distortion of porphyrin ring. By taking advantage of saddle distortion of zinc octaphenylphthalocyanine (ZnOPPc) and diprotonated dodecaphenylporphyrin (H(4)DPP(2+)), a discrete supramolecular assembly composed of Zn(OPPc) and H(4)DPP(2+) and is obtained by using 4-pyridinecarboxylate (4-PyCOO(-)) with the axial coordination bond and hydrogen bonding. The charge separation in these metal macrocycles linked with electron acceptors with axial coordination bonds is described together with the application to develop supramolecular solar cells.