Oligothiophene-containing coumarin dyes for efficient dye-sensitized solar cells

We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO(2) solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-800 nm. A solar energy-to-electricity conversion efficiency (eta) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm(-2)) with a mask: short-circuit current density (J(sc)) = 13.5 mA cm(-2); open-circuit voltage (V(oc)) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity.     

Improving the properties of the proton exchange membranes by introducing α-methylstyrene in the pre-irradiation induced graft polymerization

New proton exchange membranes (PEMs) were prepared by pre-irradiation induced grafting of α-methylstyrene (AMS)/styrene (STY)/divinylbenzene (DVB) into the crosslinked polytetrafluoroethylene (RX-PTFE) films and successively sulfonated. The new PEMs showed the improved glass transition temperature and chemical stability as compared with the PEMs prepared by pre-irradiation induced grafting of STY/DVB. The balance of the cost, grafting kinetic, thermal properties and the properties of the resulted proton exchange membrane is the key point of this work.     

Carrier generation process on photoconductive polymer films as studied by magnetic field effects on the charge-transfer fluorescence and photocurrent

We have studied the magnetic field effects (MFEs) on the charge-transfer fluorescence and transient photocurrent of a 1,2,4,5-tetracyanobenzene-doped poly(N-vinylcarbazole) film, which reflect the recombination and escape yields of the carriers, respectively. The recombination yield dependence of the external magnetic field (B) clearly shows two types of the MFEs, growth with increasing B due to the hyperfine mechanism (HFM) and a negative dip due to the level-crossing mechanism (LCM). On the other hand, the escape yield indicates complementary MFEs with a sharp decrease in yield with increasing B and then a positive dip. Simultaneous observation of the HFM- and LCM-MFEs proves the stepwise hole-hopping mechanism rather the long-range hole-jumping one. The quantitative analysis of the recombination and escape MFEs is performed using the stochastic Liouville equations (SLE) for a one-dimensional lattice model in which the stepwise hole hops take place between the nearest neighbor carbazole units with spin conservation. The SLE analysis provides the recombination and hole transfer rate constants of 7.0 x 10(7) and 4.5 x 10(8) s(-1), respectively. The boundary site number for the ion pairs in the one-dimensional model is estimated by the best fit to the experimental results. The interionic distance of the boundary ion pair in the one-dimensional model including eight sites agrees with the thermalization distance in the Onsager model. Hence, it is concluded that the elementary processes in the Onsager model applied to molecular amorphous solids are the stepwise hole hops rather than a long-range hole jump.     

Furanodictine A and B: amino sugar analogues produced by cellular slime mold Dictyostelium discoideum showing neuronal differentiation activity

We investigated the constituents of Dictyostelium discoideum to clarify the diversity of secondary metabolites of Dictyostelium cellular slime molds and to explore biologically active substances that could be useful in the development of novel drugs. From a methanol extract of the multicellular fruit body of D. discoideum, we isolated two novel amino sugar analogues, furanodictine A (1) and B (2). They are the first 3,6-anhydrosugars to be isolated from natural sources. Their relative structures were elucidated by spectral means, and the absolute configurations were confirmed by asymmetric syntheses of 1 and 2. These furanodictines potently induce neuronal differentiation of rat pheochromocytoma (PC-12) cells.     

Comproportionation reaction and hindered rotation of coordinated pyridine rings in an acetate-bridged tetraplatinum(II) cluster with pyridine-based ligands in the cluster plane

A series of pyridine-substituted derivatives of octaacetatotetraplatinum(II), [Pt4(CH3COO)8-n(L)2n]n+ (L= 4-dimethylaminopyridine (dmap), pyridine (py), 4-cyanopyridine (cpy); n = 1-4) were prepared, and the tetra- and octasubstituted forms (n = 2 and 4) were isolated. 1HNMR spectra showed that this type of cluster undergoes a comproportionation reaction. Reactions between clusters in which n = 0 and 2, n = 0 and 4, and n = 2 and 4 afforded Pt4 clusters with n = 1, 2, and 3, respectively, as a main product in acetonitrile. The dmap-substituted clusters, trans-[Pt4(CH3COO)6(dmap)4](ClO4)2 x 3CH3NO2 (3a(ClO4)2 x 3CH3NO2) and [Pt4(CH3COO)4(dmap)8](ClO4)4 x 4 H2O (5a(ClO4)4-4H2O), have been structurally characterized. Both 3a and 5a have a square-planar cluster core comprised of four PtII ions, and all eight out-of-plane coordination sites are occupied by acetate ligands in a bridging mode. In 5a, all of the in-plane sites are occupied by dmap ligands. In 3a, four dmap ligands occupy the coordination sites at the two mutually opposite edges of the square planar cluster skeleton, giving a trans tetrasubstituted form of [Pt4(CH3COO)8-] (1). In octasubstituted 5a, adjacent dmap ligands are so closely arranged that the Pt-N distances (2.20(3), 2.30(3) A) are longer than those in tetrasubstituted 3a (2.13(1), 2.15(1) A) and related Pt4 clusters. Furthermore, rotation of the dmap ligand about the Pt-N bond in 5a was restricted, and the rate constant of the rotation was 4.5s(-1) at 20 degrees C from dynamic NMR study. Cluster [Pt4(CH3COO)5(dmap)6]3+ (4a) also exhibited similar hindered rotation with the rate constants of 2.0s(-1), 12s(-1) and approximately 10(4)s(-1) at 20 degrees C depending on the coordination sites of the dmap ligands in 4a.     

Synthesis of (−)-terrecyclic acid A. Absolute configuration of terrecyclic acid A and quadrone

(?)-Terrecyclic acid A ($\text{15}$) was synthesized from (+)-fenchone ($\text{1}$). The absolute configuration of terrecyclic acid A and quadrone was established.     

Relationship between symmetry of porphyrinic pi-conjugated systems and singlet oxygen (1Delta g) yields: low-symmetry tetraazaporphyrin derivatives

We have investigated the excited-state properties and singlet oxygen ((1)Delta(g)) generation mechanism in phthalocyanines (4M; M = H(2), Mg, or Zn) and in low-symmetry metal-free, magnesium, and zinc tetraazaporphyrins (TAPs), that is, monobenzo-substituted (1M), adjacently dibenzo-substituted (2AdM), oppositely dibenzo-substituted (2OpM), and tribenzo-substituted (3M) TAP derivatives, whose pi conjugated systems were altered by fusing benzo rings. The S(1)(x) and S(1)(y) states (these lowest excited singlet states are degenerate in D(4)(h) symmetry) split in the low-symmetry TAP derivatives. The excited-state energies were quantitatively determined from the electronic absorption spectra. The lowest excited triplet (T(1)(x)) energies were also determined from phosphorescence spectra, while the second lowest excited triplet (T(1)(y)) states were evaluated by using the energy splitting between the T(1)(x) and T(1)(y) states previously reported (Miwa, H.; Ishii, K.; Kobayashi, N. Chem. Eur. J. 2004, 10, 4422-4435). The singlet oxygen quantum yields (Phi(Delta)) are strongly dependent on the pi conjugated system. In particular, while the Phi(Delta) value of 2AdH(2) is smallest in our system, that of 2OpH(2), an isomer of 2AdH(2), is larger than that of 4Zn, in contrast to the heavy atom effect. The relationship between the molecular structure and Phi(Delta) values can be transformed into a relationship between the S(1)(x) --> T(1)(y) intersystem crossing rate constant (k(ISC)) and the energy difference between the S(1)(x) and T(1)(y) states (DeltaE(S)(x)(T)(y)). In each of the Zn, Mg, and metal-free compounds, the Phi(Delta)/tau(F) values (tau(F): fluorescence lifetime), which are related to the k(ISC) values, are proportional to exp(-DeltaE(S)(x)(T)(y)), indicating that singlet oxygen ((1)Delta(g)) is produced via the T(1)(y) state and that the S(1)(x) --> T(1)(y) ISC process follows the energy-gap law. From the viewpoint of photodynamic therapy, our methodology, where the Phi(Delta) value can be controlled by changing the symmetry of pi conjugated systems without heavy elements, appears useful for preparing novel photosensitizers.     

High throughput screening of O-glycosylation conditions

We report a novel methodology for rapid and quantitative screening of O-glycosylation reactions of application to the analysis of parallel reaction systems. Our system exploits perdeuterated benzyl (Bn-d₇) ether, and stereoselectivity and yield are evaluated by ¹H NMR and MALDI-TOF MS, respectively. This paper summarizes over 240 screenings of 1 → 3 linkage formation between glucose residues targeting the α-isomer in high yield.     

Statevector reduction in discrete time: A random walk in Hilbert space

A simple model is presented in which the statevector evolves every seconds in one of two ways, according to a particular probability rule. It is shown that this random walk in Hilbert space results in reduction of the statevector. It is also shown how the continuous spontaneous localization (CSL) theory of statevector reduction is achieved as a limiting case of this model, exactly as Brownian motion is a limiting case of ordinary random walk. Finally, a slightly different but completely equivalent form of the CSL equations suggested by the simple model given here is discussed.