Femtosecond pulse excitation of vibrational wave packets in chloroform: The effect of gold nanoparticles

Excitation of pure chloroform or a gold colloid in chloroform (average nanoparticle diameter of 2.5 nm) with 740-nm femtosecond pulses of 23-fs duration leads to oscillations in the differential absorption signal ΔA(λ, t) recorded using white-light continuum. The main oscillation modes for both systems are close to the chloroform Raman resonance frequencies of 260, 367, and 668 cm⁻¹. However, marked narrowing and splitting of bands in the Fourier-transform spectra of oscillations are observed in the system of gold colloid in chloroform. The intensity of oscillations linearly increases with the pump pulse intensity in the cases of pure chloroform and the system of gold colloid in chloroform. Apparently, the principal mechanism of excitation of coherent packets in chloroform is femtosecond impulsive stimulated Raman scattering (ISRS). Dissolution of gold nanoparticles leads to a four- to sixfold enhancement of the Raman resonance signal of chloroform in the gold colloid as compared with pure chloroform. The increase in the intensity of Raman resonances is presumably due to amplification in the near field of gold nanoparticles.     

Resonance Raman spectra of metalloporphyrins. On the methine-bridge vibrations of ferric octaethylporphyrins and its α′, β′, γ′, and δ′ deutero derivatives

Raman spectra of Fe³⁺ and Pd²⁺ octaethylporphyrin (OEP) and their α′, β′, γ′, and δ′ deutero derivatives were measured with the 5145, 4880 and 4765 Å lines of an Ar ion laser. Raman bands due to methine-bridge stretching vibrations were assigned and their vibrational amplitudes were calculated from the observed frequency shifts on deuterium substitution of methine-bridge hydrogens. These vibrations correspond to the spin-state sensitive Raman bands of heme proteins. On the basis of symmetry considerations and the observed polarizations, vibrational assignments of other Raman bands were made.     

Two-photon absorption of a supramolecular pseudoisocyanine J-aggregate assembly

Linear spectral properties, including excitation anisotropy, of pseudoisocyanine or 1,1′-diethyl-2,2′-cyanine iodide (PIC) J-aggregates in aqueous solutions with J-band position at 573 nm were investigated. Two-photon absorption of PIC J-aggregates and monomer molecules was studied using an open aperture Z-scan technique. A strong enhancement of the two-photon absorption cross-section of PIC in the supramolecular J-aggregate assembly was observed in aqueous solution. This enhancement is attributed to a strong coupling of the molecular transition dipoles. No two-photon absorption at the peak of the J-band was detected.     

Raman spectrum of 1,1′-diethyl-2,2′-cyanine iodide near the π-π* electronic transition

The Raman spectrum of 1,1′-diethyl-2,2′-cyanine iodide in a methyl alcohol solution (4 × 10⁻⁵m) in which the lines of the argon ion laser at 457.9, 488.0, 496.5, 501.7 and 514.5 nm were employed as excitation sources has been investigated. The strongest lines in the Raman spectrum appear in the region from 1200–1700 cm⁻¹ and are strongly polarized (ϱ= 0.2). Two vibrational modes have been identified with reasonable certainty: one a doublet at 1361 and 1380 cm⁻¹ which involves the stretching of the conjugated chain in the ring of the quinolinic end groups, and the other at 1639 cm⁻¹ which characterizes the stretching of the conjugated chain which bridges the quinolinic end groups. The splitting of the line associated with the ring stretching mode probably arises from the resonance interaction between the two quinolinic end groups. The intensity and polarization of the lines in the spectrum indicate that the vibrational modes of the strongest lines are totally symmetric. The visible electronic spectrum shows maxima at 490.6 and 522.9nm; an analog resolution of the spectrum shows that the contour of the vibronic band can be accounted for by a vibronic progression with a spacing of approximately 1200 cm⁻¹. Both the observed variation of intensity and an approximate calculation based on A-term scattering of totally symmetric vibrational modes support the conclusion that a maximum enhancement of the intensity will be attained when the frequency of exciting radiation is equal to that of the pure electronic transition at 522.9 nm.     

Combination of Resonance and Non-Resonance Chiral Raman Scattering in a Cobalt(III) Complex

Resonance Raman optical activity (RROA) spectra with high sensitivity reveal details on molecular structure, chirality, and excited electronic properties. Despite the difficulty of the measurements, the recorded data for the Co(III) complex with S,S-N,N-ethylenediaminedisuccinic acid are of exceptional quality and, coupled with the theory, spectacularly document the molecular behavior in resonance. This includes a huge enhancement of the chiral scattering, contribution of the antisymmetric polarizabilities to the signal, and the Herzberg-Teller effect significantly shaping the spectra. The chiral component is by about one order of magnitude bigger than for an analogous aluminum complex. The band assignment and intensity profile were confirmed by simulations based on density functional and vibronic theories. The resonance was attributed to the S₀→S₃ transition, with the strongest signal enhancement of Raman and ROA spectral bands below about 800 cm⁻¹. For higher wavenumbers, other excited electronic states contribute to the scattering in a less resonant way. RROA spectroscopy thus appears as a unique tool to study the structure and electronic states of absorbing molecules in analytical chemistry, biology, and material science.     

Direct observation of a 220 cm structure in the lowest π–π* absorption band in the vapour phase of trans-azobenzene

In this work we present the first direct observation of a 220 cm⁻¹ progression in the absorption spectrum of trans-azobenzene in the vapour phase. The mode at 220 cm⁻¹ is essential to explain both the electronic absorption spectrum and the Raman excitation profiles of the most intense Raman bands of trans-azobenzene in the 1000–1600 cm⁻¹ shift range. Our data in the vapour phase assure that this frequency pertains to an internal molecular mode.     

“Adatom” sites,structure and mobility effects on the sers of cyanine

The origins of specific surface-enhanced Raman scattering (SERS) bands of 2,2′-cyanine in an electrochemical system using 488 nm excitation are discussed. Under special conditions of concentration and potential, using KI as supporting electrolyte, bands can be grouped according to their potential dependency. Experimental evidence shows that several cyanine bands are attributable to aggregated molecules. Some cyanine bands depend on the presence of different sites that can be enhanced by exposure to pulsed laser radiation; the temporal behavior of some bands indicates that different surface mobilities exist for some of the molecules.     

Enhancement mechanism of SERS from cyanine dyes adsorbed on Ag2O colloids

Surface enhancement mechanism of Raman scattering from molecules adsorbed on silver oxide colloids is reported. Absorption spectra and Raman spectra of the cyanine dye D266 and pyridine molecules adsorbed on Ag₂O colloids, and the influences of S₂O₃²⁻ and OH⁻ on the SERS are studied respectively. The results indicate that ‘chemical' enhancement is dominant in Ag₂O colloidal solution. Surface complexes of adsorbed molecules and small silver ion clusters Ag_n⁺ as the SERS active sites make an important contribution to surface enhanced Raman scattering (SERS). At these active sites, charge transfer between the adsorbed molecules and the small silver ion clusters is the main enhancement origin. The enhancement factor of D266 adsorbed on Ag₂O colloids is theoretically estimated with the excited-state charge transfer model, which is roughly in accordance with the experiments.     

The Liquid-Liquid Extraction of Copper(II), Nickel(II), and Cobalt(II) with 2,2′-Pyridil-mono-(2-quinolylhydrazone)

A 1:1 synthesis of 2-quinolylhydrazine with 2,2′-pyridil yields the hydrazone 2,2′-pyridil-mono-(2-quinolylhydrazone). In either the Z or E isomeric configuration, the molecule can serve as a tridentate ligand. Equilibrium studies were carried out to determine the effects of pH and concentration of ligand and metal on the distribution of the extracted complex into methyl isobutyl ketone. Graphical analysis of the slopes of the plot of the logarithm of the distribution coefficient vs pH, log [ligand], and log [M(II)] will determine the stoichiometry and polymerization of the complex. In the extraction of Cu(II), Ni(II), and Co(II), there is a small change in log D, where D is the distribution coefficient, with pH indicating the presence of a weakly dissociated ligand. Ligand:metal (1:1) ion-paired species are extracted, each having three absorption peaks in the region 400-550 nm. While a spectrophotometrtc method for each element does not seem feasible due to simultaneous extraction and overlapping absorbances, an extractive-atomic absorption method for the analysis of 1.6 ppm of Cu(II) is presented. Excesses of 20-70 ppm Co(II), Zn(II), Cd(II), Cl⁻, NO₃⁻, and SO₄²⁻ do not interfere.     

Synthesis, characterization and crystal structure determination of platinum(IV) complexes containing, bipyridine derivatives and chloride, [Pt(5,5′-dmbipy)Cl4] and [Pt(6-mbipy)Cl4]

The complex [Pt(5,5′-dmbipy)Cl₄] (1) (5,5′-dmbipy is 5,5′-dimethyl-2,2′-bipyridine) was prepared from the reaction of H₂PtCl₆·6H₂O with 5,5′-dimethyl-2,2′-bipyridine in methanol. The same method was employed to make [Pt(6-mbipy)Cl₄] (2) (6-mbipy is 6-methyl-2,2′-bipyridine). Both complexes were characterized by elemental analysis, IR, UV–Vis, ¹H NMR, ¹³C NMR and ¹⁹⁵Pt NMR spectroscopy. Their solid state structures were determined by the X-ray diffraction method.     

Fourier-transform surface-enhanced Raman scattering study on thiourea and some substituted thioureas adsorbed on chemically deposited silver films

Adsorption of thiourea, N,N′-diphenylthiourea (DIPTU), N-ethyl-N′-phenylthiourea (ETPTU) and N-(p-nitrophenyl)thiourea (NPTU), from acidic and neutral solutions, on chemically deposited silver film substrates are investigated using Fourier transform surface-enhanced Raman scattering (FT-SERS) technique. A strong band in the low frequency region, around 230 cm⁻¹ in the FT-SERS spectra of all these systems, assigned to Ag–S stretch, indicates a preferential adsorption through the sulfur atom. The frequencies and bandwidths of benzene ring vibrational modes in ETPTU as well as DIPTU are almost unaffected by adsorption indicating that benzene rings do not interact directly with the silver surface. A cis-cis conformation (both imino H-atoms cis with respect to thione sulfur atom) is proposed for DIPTU and ETPTU on the silver surface. In the case of NPTU, an additional interaction through the benzene ring is also observed as shown by the frequency shifts and band broadening of some benzene ring modes and weak intensity of the C–H stretching band.     

Synthesis and characterization of novel α- or β-tetra[6,7-dihexyloxy-3-(4-oxyphenyl)coumarin]-substituted metal-free and metallo phthalocyanines

The synthesis of novel phthalonitriles substituted at 3- or 4-position with 6,7-dihexyloxy-3-(4-oxyphenyl)coumarin were performed. The metal-free and metallo phthalocyanines (MPcs) (M = Zn, Co, Cu) were prepared by cyclotetramerization of 6,7-dihexyloxy-3-[p-(2′,3′-dicyanophenoxy)phenyl]coumarin or 6,7-dihexyloxy-3-[p-(3′,4′-dicyanophenoxy)phenyl]coumarin. The newly prepared compounds, phthalonitriles and Pcs, have been characterized by elemental analysis, ¹H NMR, ¹³C NMR, MALDI-TOF, IR, UV–Vis and fluorescence spectral data. The electronic spectra exhibit bands of coumarin identity along with characteristic Q and B bands of the Pc core. The IR-spectra of all Pcs showed three characteristic intense bands at 1709–1700 cm⁻¹ for lactone carbonyl, two bands at 1489–1604 cm⁻¹ for conjugated olefinic system.     

Enantiomeric Discrimination by Surface‐Enhanced Raman Scattering–Chiral Anisotropy of Chiral Nanostructured Gold Films

A surface‐enhanced Raman scattering‐chiral anisotropy (SERS‐ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS‐ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs.     

DNA-binding studies of mixed ligand cobalt(III) complexes

The DNA binding characteristics of mixed ligand complexes of the type [Co(en)₂(L)]Br₃ where en = N,N′-ethylenediamine and L = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 1,10-phenanthroline-5,6-dione (phendione), dipyrido[3,2-a:2′,3′-c]phenazine (dppz) have been investigated by absorption titration, competitive binding fluorescence spectroscopy and viscosity measurements. The order of intercalative ability of the coordinated ligands is dppz > phen > phendione > bpy in this series of complexes.     

Synthesis and spectroscopic properties of a new bipyridine-bipyrazoyl(pyridine)-thiocyanato-ruthenium(II) complex

The complex [Ru(II)(dcbpyH₂)(bdmpp)NCS](PF₆) (1) (where dcbpyH₂ is 2,2′-bipyridine-4,4′-dicarboxylic acid, bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine,) is synthesized and characterized extensively by ¹H NMR and ¹³C NMR 1D and 2D, mass spectroscopy, cyclic voltammetry, electronic absorption spectroscopy and IR. The half-wave potential of the Ru(II)/Ru(III) redox couple was measured at E_1/2=+0.795 V versus Ag/AgCl in CH₃CN. The complex presents three intense metal-to-ligand charge transfer (MLCT) (d_M→π_L*) absorption bands centered at 383 (=21 300 M⁻¹ cm⁻¹), 432 (=22 400 M⁻¹ cm⁻¹) and 475 nm (=23 400 M⁻¹ cm⁻¹), respectively. The absorbance is extremely strong between 400 and 500 nm and even at 620 nm, the extinction coefficient is still high (=3768 M⁻¹ cm⁻¹). The strong π-acceptor property of the trans-isothiocyanate ligand compared with the Cl⁻ ligand is probably the cause of the blue-shift observed in complex 1. These properties make the complex potentially promising for the photosensitization process. The incorporation of TiO₂ photoelectrodes derivatized with this complex into a solar cell using a composite polymer/inorganic oxide solid-state electrolyte confirmed its sensitizing ability. Incident monochromatic photon-to-current conversion efficiency (IPCE) values of about 30% and overall energy conversion efficiency (η) of 1.7% were obtained.     

Electro-oxidation of o-aminophenol studied by cyclic voltammetry and surface enhanced Raman scattering (SERS)

Cyclic voltammetry and surface enhanced Raman scattering (SERS) spectra were used over a wide pH range to examine the products of o-aminophenol oxidation on a roughened silver electrode. The results of the study indicated that at least two oxidation products are formed at the stationary potential of the electrode. The major product in alkaline and neutral media was identified as 2,2′-dihydroxyazobenzene, a linear dimer formed by N---N coupling of o-aminophenol cation radicals. In acidic solutions the cyclic dimer 3-aminophenoxazone formed by C---N coupling of o-aminophenol cation radicals dominates on the silver electrode.     

Rotational analysis of the v7,v11 (a′,a″) pair of bands of the infrared spectrum of the deuterium substituted propynal molecule C2H-CDO

The mid-infrared spectrum of the v₇,v₁₁ (a′,a″) pair of bands of the deuterium substituted propynal molecule C₂H-CDO was recorded at a resolution of about 0.08 cm⁻¹. An analysis of the pair of bands was completed using the method of simulation of the observed bands with synthetic spectra taking into account the effects of second order Coriolis interactions between the energy levels of the two bands. Best fit values for the changes in the rotational constants (A″ − A′), (B″ − B′) and (C″ − C′), the second order Coriolis constant ζ_7,11 and the δ_7,11 = v₁₁ − v₇ constant have been derived.     

Novel Silver/Poly(vinyl alcohol) Nanocomposites for Surface‐Enhanced Raman Scattering‐Active Substrates

Summary: Surface‐enhanced Raman scattering (SERS)‐active substrates with high enhancement were prepared by an in situ reduction method. Novel silver/poly(vinyl alcohol) (PVA) nanocomposite films were obtained, in which the silver nitrate, poly(γ‐glutamic acid) (PGA), and PVA acted as precursor, stabilizer, and polyol reducant, respectively. The UV‐visible spectra of the as‐fabricated films showed that the surface plasmon resonance (SPR) absorption band was narrow and of a stronger intensity, which indicates that the Ag nanoparticle size distribution on the substrate was highly uniform. This finding was further confirmed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and field‐emission scanning electron microscope (FE‐SEM) measurements. It was found that a PGA‐stabilized PVA nanocomposite film revealed the presence of well‐dispersed spherical silver nanoparticles with an average diameter of 90 nm. The new substrate presents high SERS enhancement and the enhanced factor is estimated to be 10⁶ for the detection of benzoic acid.

The Raman scattering enhancement factor for the Raman spectra of benzoic acid on the various nanocomposite films.     

Absorption,Fluorescence and Resonance Rayleigh Scattering Spectra of Interaction of Papain with Calf Thymus DNA

In weak acidic medium, interaction between papain and calf thymus DNA (ctDNA) resulted in absorption spectral change, fluorescence quenching of papain and remarkable enhancement of resonance Rayleigh scattering (RRS). The interaction types and binding modes were discussed by characteristics of RRS, absorption, fluorescence and circular dichroism spectra combining thermodynamic data. Four interaction types include electrostatic attraction, hydrophobic force, hydrogen bonding and aromatic stacking interaction. Papain interacted with the major groove of ctDNA. Aromatic stacking interaction is the main reason of change of absorption spectrum and fluorescence quenching of papain. Surface enhanced scattering effect, resonance energy transfer effect, increase of molecular volume and conformational change make contribution to RRS enhancement. The enhanced RRS intensity (ΔI) is directly proportional to the concentration of ctDNA or papain. The detection limit (3σ) is 5.2 ng·mL^?1 for ctDNA and 5.6 ng·mL^?1 for papain. This creates conditions for determination of papain and ctDNA.     

Characterization of the Fe(III)‐binding Site in Sepia Eumelanin by Resonance Raman Confocal Microspectroscopy¶

The resonance Raman spectrum of Sepia eumelanin is discussed by analogy to model compounds containing catechol (CAT)‐like structural units. These data are then compared with the analogous data on Fe(III)‐enriched Sepia eumelanin. In contrast to the natural eumelanin, the Fe(III)‐enriched samples exhibit absorption features in the visible and near‐IR spectral regions, which are attributed to ligand‐to‐metal charge‐transfer (LMCT) bands. Resonance Raman spectra collected by exciting these LMCT bands reveal bands at 580 and 1470 cm^?1; the intensity of these features increases wioth increasing Fe(III) content. The 580 and 1470 cm^?1 bands are assigned to Fe‐OR stretching and ring deformation modes, respectively. These data further substantiate that the Fe(III)‐ melanin‐binding site in melanin is composed of CAT‐like structural units.