Molecular engineering of organic sensitizers containing p-phenylene vinylene unit for dye-sensitized solar cells

Three organic sensitizers containing bis-dimethylfluorenyl amino donor and a cyanoacrylic acid acceptor bridged by p-phenylene vinylene unit were synthesized. The power conversion efficiency was quite sensitive to the length of bridged phenylene vinylene groups. A nanocrystalline TiO2 dye-sensitized solar cell was fabricated using three sensitizers. The maximum power conversion efficiency of JK-59 reached 7.02%.     

Enantioselective Rhodium-Catalyzed Pauson–Khand Reactions of 1,6-Chloroenynes with 1,1-Disubstituted Olefins

An enantioselective rhodium(I)-catalyzed Pauson–Khand reaction (PKR) using 1,6-chloroenynes that contain challenging 1,1-disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which are only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non-polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre-polarizes the alkyne to lower the barrier for metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand. Hence, the chloroalkyne enables the efficient and enantioselective PKR with 1,6-enynes that contain challenging 1,1-disubstituted olefins, thereby representing a new paradigm for enantioselective reactions involving 1,6-enynes.     

Electronic structure and magnetism in transition metals doped 8-hydroxy-quinoline aluminum

We report the room-temperature ferromagnetism in transition metals (Co, Ni)-doped 8-hydroxy-quinoline aluminum (Alq3) by thermal coevaporation of high purity metal and Alq3 powders. For 5% Co-doped Alq3, a maximum magnetization of approximately 0.33 microB/Co at 10 K was obtained and ferromagnetic behavior was observed up to 300 K. The Co atoms interact chemically with O atoms and provide electrons to Alq3, forming new states acting as electron trap sites. From this, it is suggested that ferromagnetism may be associated with the strong chemical interaction of Co atoms and Alq3 molecules.     

The mechanism of the rhodium(I)-catalyzed [2 + 2 + 1] carbocyclization reaction of dienes and CO: a computational study

The rhodium(I) catalyzed [2 + 2 + 1] carbocyclization of tethered diene-enes to afford substituted hexahydropentalenones with high levels of diastereoselectivity was modeled using density functional theory. Previously, this transformation was observed to be facile, whereas the analogous bis-ene substrate could not be cyclized under any reasonable conditions. To establish a conceptual understanding of the carbocyclization mechanism and to identify the functional role of the diene fragment we analyzed the simulated reaction mechanisms using the two parent systems. We discovered a thus far unrecognized, but intuitively plausible, role of the CO ligand for controlling the electron density at the metal center, which affects the feasibility of oxidative addition and reductive elimination steps that are key components of the mechanism. Our calculations suggest that the diene moiety is unique and required because of its ability to undergo a eta(2)-->eta(4) reorganization allowing for the thermoneutral expulsion of one CO ligand, which in turn generates an electron-rich, coordinatively saturated Rh(I) center that can efficiently promote the oxidative addition with a low barrier. A number of functionalization strategies were considered explicitly to derive a rational plan for optimizing the catalysis and to expose the roles of the different components of the reactant-catalyst complex.     

Lewis acid stabilized methylidene and oxoscandium complexes

The methylidene scandium complex (PNP)Sc(mu3-CH2)(mu2-CH3)2[Al(CH3)2]2 (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can be prepared from the reaction of (PNP)Sc(CH3)2 and 2 equiv of Al(CH3)3. The Lewis acid stabilized methylidenes candium complex has been crystallographically characterized, and its bonding scheme analyzed by DFT. In addition, we report preliminary reactivity studies of the Sc-CH2 ligand with substrates such as H2NAr and OCPh2. While the former results in an Br?nsted acid-base reaction, the latter reagent produces the olefin H2C CPh2 along with the novel oxoscandium complex (PNP)Sc(mu3-O)(mu2-CH3)2[Al(CH3)2]2, quantitatively.     

Right-angled Artin groups in the C∞ diffeomorphism group of the real line

We prove that every right-angled Artin group embeds into the C^∞ diffeomorphism group of the real line. As a corollary, we show every limit group, and more generally every countable residually RAAG group, embeds into the C^∞ diffeomorphism group of the real line.     

Electrical transport characteristics of surface-conductance-controlled, dielectrophoretically separated single-walled carbon nanotubes

Alternating current dielectrophoresis has attracted considerable attention as a possible candidate to separate single-walled carbon nanotubes according to electronic types. Recently, the significant effect of surface charge on the polarizability of semiconducting nanotubes was demonstrated using comparative Raman spectroscopic studies. Here we present electrical transport characteristics of surface-charge-controlled, dielectrophoretically deposited nanotube arrays. The surface charge was controlled using cationic/anionic surfactant mixtures. Complete separation between metallic and semiconducting species was achieved at the electric field frequency of 10 MHz only when the surface charge of nanotubes was neutralized, which is consistent with previous Raman investigation. A theoretical analysis, using zeta potential information as input, further supported the experimental observation.     

Limiting Distributions for a Polynuclear Growth Model with External Sources

The purpose of this paper is to investigate the limiting distribution functions for a polynuclear growth model with two external sources which was considered by Prähofer and Spohn. Depending on the strength of the sources, the limiting distribution functions are either the Tracy–Widom functions of random matrix theory or a new explicit function which has the special property that its mean is zero. Moreover, we obtain transition functions between pairs of the above distribution functions in suitably scaled limits. There are also similar results for a discrete totally asymmetric exclusion process.