Harvesting infrared photons with tricarbocyanine dye clusters

The absorption of 4,5-benzoindotricarbocyanine dye (IR125) in the infrared can be tuned by controlling the type of aggregation in different media. Molecular clusters of this dye formed in a mixed solvent show broad absorption in the 550-950 nm region as compared to the absorption bands of J- and H-type aggregates. The molecular clusters of the carbocyanine dye are electrophoretically deposited as thin film on optically transparent electrodes using a dc electric field. These tricarbocyanine dye cluster films are photoactive in the infrared region and produce cathodic current when employed as photocathode in a photoelectrochemical cell. Transient absorption spectroscopy of the molecular clusters show short-lived singlet state in the picosecond time scale (lifetime 6 ps) and a charge separated state in the nanosecond time scale. Implication of such dye cluster films for harvesting infrared photons in a photoelectrochemical cell is discussed.     

Ultrafast cooling of photoexcited electrons in gold nanoparticle-thiolated DNA conjugates involves the dissociation of the gold-thiol bond

Using UV-visible extinction spectroscopy and femtosecond pump-probe transient absorption spectroscopy, we have studied the effect of femtosecond laser heating on gold nanoparticles attached to DNA ligands via thiol groups. It is found that femtosecond pulse excitation of the DNA-modified nanoparticles at a wavelength of 400 nm leads to desorption of the thiolated DNA strands from the nanoparticle surface by the dissociation of the gold-sulfur bond. The laser-initiated gold-sulfur bond-breaking process is a new pathway for nonradiative relaxation of the optically excited electrons within the DNA-modified gold nanoparticles, as manifested by a faster decay rate of the excited electronic distribution at progressively higher laser pulse energies. The experimental results favor a bond dissociation mechanism involving the coupling between the photoexcited electrons of the nanoparticles and the gold-sulfur bond vibrations over one involving the conventional phonon-phonon thermal heating processes. The latter processes have been observed previously by our group to be effective in the selective photothermal destruction of cancer cells bound to anti-epidermal growth factor receptor-conjugated gold nanoparticles.     

CpNi(dithiolene)] (and diselenolene) neutral radical complexes

Various preparations of the neutral radical [CpNi(dddt)] complex (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were investigated with CpNi sources, [Cp2Ni], [Cp2Ni](BF4), [CpNi(CO)]2, and [CpNi(cod)](BF4), and dithiolene transfer sources, O=C(dddt), the naked dithiolate (dddt(2-)), the monoanion of square-planar Ni dithiolene complex (NBu4)[Ni(dddt)2], and the neutral complex [Ni(dddt)2]. The reaction of [CpNi(cod)](BF4) with (NBu4)[Ni(dddt)2] gave the highest yield for the preparation of [CpNi(dddt)] (86%). [CpNi(ddds)] (ddds = 5,6-dihydro-1,4-dithiin-2,3-diselenolate), [CpNi(dsdt)] (dsdt = 5,6-dihydro-1,4-diselenin-2,3-dithiolate), [CpNi(bdt)] (bdt = 1,2-benzenedithiolate), and [CpNi(bds)] (bds = 1,2-benzenediselenolate) were synthesized by the reactions of [Cp2Ni] with the corresponding neutral Ni dithiolene complexes [Ni(ddds)2]2, [Ni(dsdt)2], [Ni(bdt)2], and [Ni(bds)2], respectively. The five, formally Ni(III), radical complexes oxidize and reduce reversibly. They exhibit, in the neutral state, a strong absorption in the NIR region, from 1000 nm in the dddt/ddds/dsdt series to 720 nm in the bdt/bds series with epsilon values between 2500 and 5000 M(-1) cm(-1). The molecular and solid state structures of the five complexes were determined by X-ray structure analyses. [CpNi(dddt)] and [CpNi(ddds)] are isostructural, while [CpNi(dsdt)] exhibits a closely related structure. Similarly, [CpNi(bdt)] and [CpNi(bds)] are also isostructural. Correlations between structural data and magnetic measurements show the presence of alternated spin chains in [CpNi(dddt)], [CpNi(ddds)], and [CpNi(dsdt)], while a remarkably strong antiferromagnetic interaction in [CpNi(bdt)] and [CpNi(bds)] is attributed to a Cp...Cp face-to-face sigma overlap, an original feature in organometallic radical complexes.     

Heteroleptic rhodium complexes containing both the dipyrrin/cyclooctadiene ligands and application of [(η-C8H12)Rh(4-pyrdpm)] in the construction of homo-/hetero-bimetallic complexes

Heteroleptic rhodium(I) complexes with the general formulations [(η⁴-C₈H₁₂)Rh(L)] [η⁴-C₈H₁₂ = 1,5-cyclooctadiene; L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene, ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm; 5-(4-pyridyl)dipyrromethene, 4-pyrdpm; 5-(3-pyridyl)dipyrromethene, 3-pyrdpm] have been synthesized. The complex [(η⁴-C₈H₁₂)Rh(4-pyrdpm)] have been used as a synthon in the construction of homo-bimetallic complex [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Rh(η⁵-C₅Me₅)Cl₂] and hetero-bimetallic complexes [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ir(η⁵-C₅Me₅)Cl₂], [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ru(η⁶-C₁₀H₁₄)Cl₂] and [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ru(η⁶-C₆H₆)Cl₂]. Resulting complexes have been characterized by elemental analyses and spectral studies. Molecular structures of the representative mononuclear complexes [(η⁴-C₈H₁₂)Rh(ndpm)] and [(η⁴-C₈H₁₂)Rh(4-pyrdpm)] have been authenticated crystallographically.     

A finite element approach for finding positive solutions of semilinear elliptic Dirichlet problems

In the present article, we described the finite element method for finding positive solutions for the elliptic problems of the type ‐ Δu = λf(x)g(u) for x ε Ω, with Dirichlet boundary condition. By using Matlab, we visualize the range of λ in which this problem achieves a numerical solution, and also discussed the behavior of the branch of this solution. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009     

In situ Raman microscopy during discharge of a high capacity silicon–carbon composite Li-ion battery negative electrode

In situ Raman microscopy study has been performed in order to characterize the surface of the Si/C composite anode and also to monitor the alloying/dealloying behavior of Si/C with Li ion during electrochemical discharging/charging processes at a microscopic level. This study shows that the Si particles are covered by graphite and hard carbon, with demonstration of further evidence of amorphisation of silicon and presence of mixed phases of Li–Si.     

Modeling antimalarial and antihuman African trypanosomiasis compounds: a ligand- and structure-based approaches

Molecular Diversity - This study examines the interaction of 137 antimalarial and antihuman African trypanosomiasis compounds [bis(2-aminoimidazolines), bisguanidinediphenyls and polyamines] on...     

3D highly porous microspherical morphology of NiO nanoparticles for supercapacitor application

Journal of Solid State Electrochemistry - In the present work, the effect of reaction temperature and urea concentration on the electrochemical performance of NiO nanoparticles is investigated. The...     

Copper-Catalyzed Intramolecular SEAr Reaction–Oxidation under Aerobic Conditions: Synthesis of Styryl-/Alkenyl-Substituted Xanthone Derivatives

Herein, we report a copper-catalyzed intramolecular electrophilic aromatic substitution (S_EAr)−oxidation process to access a wide range of diversified xanthone derivatives using air as a sole oxidant. Specifically, this protocol affords hitherto unknown styryl-/alkenyl-substituted xanthone derivatives in moderate to high yields. The practicality of the method has been demonstrated by gram-scale syntheses.