Properties of copper (fluoro-)phthalocyanine layers deposited on epitaxial graphene

We investigate the atomic structure and electronic properties of monolayers of copper phthalocyanines (CuPc) deposited on epitaxial graphene substrate. We focus in particular on hexadecafluorophthalocyanine (F(16)CuPc), using both theoretical and experimental (scanning tunneling microscopy - STM) studies. For the individual CuPc and F(16)CuPc molecules, we calculated the electronic and optical properties using density functional theory (DFT) and time-dependent DFT and found a red-shift in the absorption peaks of F(16)CuPc relative to those of CuPc. In F(16)CuPc, the electronic wavefunctions are more polarized toward the electronegative fluorine atoms and away from the Cu atom at the center of the molecule. When adsorbed on graphene, the molecules lie flat and form closely packed patterns: F(16)CuPc forms a hexagonal pattern with two well-ordered alternating α and β stripes while CuPc arranges into a square lattice. The competition between molecule-substrate and intermolecular van der Waals interactions plays a crucial role in establishing the molecular patterns leading to tunable electron transfer from graphene to the molecules. This transfer is controlled by the layer thickness of, or the applied voltage on, epitaxial graphene resulting in selective F(16)CuPc adsorption, as observed in STM experiments. In addition, phthalocyanine adsorption modifies the electronic structure of the underlying graphene substrate introducing intensity smoothing in the range of 2-3 eV below the Dirac point (E(D)) and a small peak in the density of states at ～0.4 eV above E(D).     

Synthesis, structures, and reactivity of yttrium alkyl and alkynyl complexes with mixed Tp(Me2)/Cp ligands

The structurally characterized Tp(Me2)-supported rare earth metal monoalkyl complex (Tp(Me2))CpYCH(2)Ph(THF) (1) was synthesized via the salt-metathesis reaction of (Tp(Me2))CpYCl(THF) with KCH(2)Ph in THF at room temperature. Treatment of 1 with 1 equiv of PhC≡CH under the same conditions afforded the corresponding alkynyl complex (Tp(Me2))CpYC≡CPh(THF) (2). Complex 1 exhibits high activity toward carbodiimides, isocyanate, isothiocyanate, and CS(2); treatment of 1 with such substrates led to the formation of a series of the corresponding Y-C(benzyl) σ-bond insertion products (Tp(Me2))CpY[(RN)(2)CCH(2)Ph] (R = (i)Pr(3a), Cy(3b), 2,6-(i)Pr-C(6)H(3)(3c)), (Tp(Me2))CpY[SC(CH(2)Ph)NPh] (4), (Tp(Me2))CpY[OC(CH(2)Ph)NPh] (5), and (Tp(Me2))CpY(S(2)CCH(2)Ph) (6) in 40-70% isolated yields. Carbodiimides and isothiocyanate can also insert into the Y-C(alkynyl) σ bond of 2 to yield complexes (Tp(Me2))CpY[(RN)(2)CC≡CPh] (R = (i)Pr(7a), Cy(7b)) and (Tp(Me2))CpY[SC(C≡CPh)NPh] (9). Further investigation results indicated that 1 can effectively catalyze the cross-coupling reactions of phenylacetylene with carbodiimides. However, treatment of o-allylaniline with a catalytic amount of 1 gave only the benzyl abstraction product (Tp(Me2))CpY(NHC(6)H(4)CH(2)CH═CH(2)-o)(THF) (10), without observation of the expected organic hydroamination/cyclization product. All of these new complexes were characterized by elemental analysis and spectroscopic properties, and their solid-state structures were also confirmed by single-crystal X-ray diffraction analysis.     

Active cobalt catalyst for the cleavage of benzyl ether

An improved method for the deprotection of benzyl ethers using a catalytic amount of Co(2)(CO)(8) in the presence of Me(2)PhSiH and CO (1 atm) is described. The deprotection reaction is compatible with double bond or sulfur-containing substrates. The method also tolerates other functional groups, such as Ac, Piv, and Bz, and shows potential selectivity in perbenzylated monosaccharides.     

BF3·OEt2-promoted diastereoselective diacetoxylation of alkenes by PhI(OAc)2

Selective syn and anti diacetoxylations of alkenes have been achieved using a PhI(OAc)(2)/BF(3)·OEt(2) system in the presence and absence of water, respectively. A broad range of substrates including electron-deficient alkenes (such as α,β-unsaturated esters) could be elaborated efficiently at room temperature with this methodology, furnishing the desired products in good to excellent yields and diastereoselectivity. In particular, a multigram-scale diastereoselective diacetoxylation of methyl cinnamate (5.00 g) was also accomplished in a few hours, maintaining the same efficiency as small-scale reaction. This novel methodology provides an alternative approach for the preparation of various 1,2-diols.     

Femtosecond dynamics of the ring closing process of diarylethene: a case study of electrocyclic reactions in photochromic single crystals

The cyclization reaction of the photochromic diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene was studied in its single crystal phase with femtosecond transient absorption spectroscopy. The transient absorption measurements were performed with a robust acquisition scheme that explicitly exploits the photoreversibility of the molecular system and monitors the reversibility conditions. The crystalline system demonstrated 3 × 10(4) repeatable cycles before significant degradation was observed. Immediately following photoexcitation, the excited state absorption associated with the open-ring conformation undergoes a large spectral shift with a time constant of approximately 200 fs. Following this evolution on the excited state potential energy surface, the ring closure occurs with a time constant of 5.3 ps, which is significantly slower than previously reported measurements for similar derivatives in the solution phase. Time resolved electron diffraction studies were used to further demonstrate the assignment of the transient absorption dynamics to the ring closing reaction. The mechanistic details of the ring closing are discussed in the context of prior computational work along with a vibrational mode analysis using density functional theory to give some insight into the primary motions involved in the ring closing reaction.     

Interactions of single-stranded DNA on microcantilevers

The microcantilever approach has attracted considerable attention in recent years as a means of label-free detection of a variety of biomolecular and chemical reactions. The underlying physics of the intermolecular interactions that result in mechanical motions is yet to be fully explored, but it seems both rich in science and of technological importance. This paper presents an overview of experiments and theories related to interactions of single-stranded DNA immobilized on microcantilevers. Experiments and theories show that, at high grafting density, hydration forces are the dominant factor determining cantilever deflections, not electrostatics or conformational entropy.     

Label-free fluorescent detection of Cu(II) ions based on DNA cleavage-dependent graphene-quenched DNAzymes

We developed a novel and general methodology to design a label-free fluorescent Cu(II) sensor based on internal DNA cleavage and an extrinsic fluorophore in a graphene/DNAzymes complex with high sensitivity and selectivity.     

Optically pure bulky (hetero)arylalkyl carbinols via kinetic resolution

Planar chiral nucleophilic catalyst Fc-PIP was employed in the kinetic resolution of bulky (hetero)arylalkyl carbinols delivering unreacted alcohols with extremely high enantiomeric excess (>99.0% ees) in ideal conversions ranging from 50.4-56.7%.     

FITC-modified PPy nanotubes embedded in nanoporous AAO membrane can detect trace PCB20 via fluorescence ratiometric measurement

A highly sensitive and selective fluorescence ratiometric sensor membrane for 2,3,3'-trichlorobiphenyl has been achieved, via depositing polypyrrole nanotubes (PPyNTs, the fluorescence indicator) in nano-porous anodic aluminium oxide (NPAAO) template and subsequently immobilizing fluorescein isothiocyanate (as an internal reference) onto the inner walls of the PPyNTs embedded in the NPAAO.     

Nucleic acids determination using the complex of eriochrome black T and silver nanoparticles in a resonance light scattering technique

A novel method for the determination of nucleic acids by using silver nanoparticle (AgNPs)-eriochrome black T (EBT) as a resonance light scattering (RLS) probe has been developed. Under optimum conditions, there are linear relationships between the quenching extent of RLS intensity and the concentration of nucleic acids in the range of 4.0×10(-9)-4.0×10(-7), 4.0×10(-7)-1.6×10(-6) g mL(-1) for fish sperm DNA (fsDNA) and 4.0×10(-8)-2.0×10(-6) g mL(-1) for yeast RNA (yRNA). Their detection limits (S/N=3) are 2.0 ng mL(-1) and 21 ng mL(-1), respectively. The results indicate that AgNPs can form wirelike aggregates and nanoslices in the presence of the EBT. Whereas, when nucleic acids are added into the AgNPs-EBT system, the dynamic balance of AgNPs-EBT system is destroyed and the nanoparticles undergo dispersion again, leading to the RLS intensity of AgNPs-EBT system quenching. Meanwhile, the conformation of fsDNA is changed by the synergistic effect of AgNPs and EBT.