Spectral investigations on 1,5-dipiperidino anthraquinone

Optical absorption, fluorescence emission and surface enhanced Raman spectra of 1,5-dipiperidino anthraquinone (1,5-DPAQ) have been examined to elucidate the nature of molecule in different environments. Fluorescence emission and optical absorption measurements show that the polarity of the solvent plays a vital role through intermolecular hydrogen bonding and reorientational motion of solvent molecule around excited state fluorophore. Anisotropy measurement gives the angle between absorption and emission transition dipoles. The vibrational features observed in surface enhanced Raman spectroscopy (SERS) suggest that the molecules are chemisorbed. The adsorption of the molecule is through pi electrons in the anthraquinone ring and the axial lone pair of electrons of nitrogen. The orientation of the molecule is found to be 'flat-on'.     

Spectral investigations of preferential solvation and solute-solvent interactions of 1,4-dimethylamino anthraquinone in CH2Cl2/C2H5OH mixtures

The optical absorption and IR spectra of 1,4-dimethylamino anthraquinone (1,4-DMAAQ) in CH(2)Cl(2)/C(2)H(5)OH mixtures have been investigated. The preferential solvation of 1,4-DMAAQ in CH(2)Cl(2)/C(2)H(5)OH mixed solvents has been studied by monitoring the charge transfer band of 1,4-DMAAQ. The optical absorption spectral study indicates that 1,4-DMAAQ is preferentially solvated by CH(2)Cl(2) in CH(2)Cl(2)/C(2)H(5)OH mixtures. This can be confirmed by the observed index of preferential solvation value (delta(s1)) as well as higher mole fraction of CH(2)Cl(2) in the solvation microsphere (x(1)(L)) than in the bulk solvent (x(1)). The CH(2)Cl(2) molecules become more available to enter the solvation shell of 1,4-DMAAQ because of the hydrogen bonded clusters formed by ethanol molecules. This is also evident from the non-linear behavior of the transition energy (E(12)) as well as the absence of synergistic behavior. IR spectral studies show that the observed shifts in the nu(CO) and nu(NH) of 1,4-DMAAQ are due to the dipole-dipole interaction between the 1,4-DMAAQ and the associated ethanol.     

Two-step laser excitation fluorescence study of the magnetic field effect on the hydrogen abstraction reaction of anthraquinone in SDS micellar solution

The magnetic field effect on the hydrogen abstraction reaction of anthraquinone in sodium dodecyl sulfate (SDS) micellar solution has been studied by two-step laser excitation fluorescence including a variable delay technique. The risetime of the “cage product” is 380 ns at 0 G and 890 ns at 800 G, while its yield decreases by 20% at 800 G. The results are interpreted in terms of the radical pair model of CIDNP.     

Structural luminescence spectra of biogenous porphyrins under selective laser excitation and dependence of this effect on excitation wavelength

Selective laser excitation removes an inhomogeneous width in wideband luminescence spectra of solid solutions of biogenous porphyrins resulting in spectra consisting of narrow zero-phonon lines and phonon sidebands. The effect depends strongly on excitation frequency and disappears gradually upon increasing this frequency within the inhomogeneously broadened pure electronic transition band.     

Ab initio quantum-mechanical characterization of the electronic states of anthraquinone,quinizarin, and 1,4-diamino anthraquinone

The ground and excited singlet and triplet states of 9,10-anthraquinone and its 1,4-dihydroxy and 1,4-diamino derivatives are investigated by ab initio configuration interaction calculations, using a floating Gaussian basis. For anthraquinone the calculated electronic absorption spectrum is consistent with previous experimental and theoretical results. The possible mechanisms of intersystem crossing and intensity borrowing in phosphorescence are discussed in terms of first- and second-order spin-orbit and vibronic perturbations of the computed singlet and triplet states. The calculated spectra of the 1,4-disubstituted derivatives are more complex than previously suggested from low-resolution polarized absorption studies. The principal effect of 1,4-substitution by electron donating groups is shown to be a powerful conjugative effect which significantly modifies selected molecular orbitals of anthraquinone; the resultant effect on the absorption spectra is the creation of two new substituent-induced π → π* transitions, one of which corresponds to the intense visible absorption band of these systems.     

Spectral investigations on melanterite mineral from France.

EPR, Optical and IR spectral studies on a naturally occurring mineral melanterite are carried out at room temperature. EPR studies indicate the presence of Cu(II) ion in tetragonally distorted octahedral site and hyperfine lines could not be resolved due to higher concentration of the paramagnetic impurity in the mineral. Optical absorption spectrum is a characteristic of Fe(II) and Cu(II) ions. Crystal field parameters are evaluated. IR spectrum confirms the presence of water and sulphate ions.     

Spectral investigations of amino acid picrates

FTIR and laser Raman spectra of beta-alanine beta-alaninium picrate and dl-phenylalanine dl-phenylalaninium picrate crystals of space group P1 (C(i)) have been me in the 4000-50 cm(-1) range, at room temperature. The former crystal consists of beta-alanine beta-alaninium and the later dl-phenylalanine dl-phenylalaninium as cations. The presence of both carbonyl (CO) and carboxylate COO(-) groups in these crystals is the evidence for the existence of the zwitterion and the protonated forms. Factor group analysis has been made and the numbers of vibrational modes have been calculated. The tentative assignments of the observed bands are given. Fermi resonance has also been observed in one of the crystal beta-alanine beta-alaninium picrate. The picrate group forms the anion in both crystals and the characteristic bands nu(as)NO(2), nu(s)NO(2), and nu(phen)C-O stretching are observed in the spectra. These suggest that the picrate ion is unaffected by the presence of the cations.     

Spectral and magnetic investigations on some binuclear oxovanadium compounds

Several binuclear oxovanadium compounds of binucleating ligands are synthesised and investigated by magnetic, spectral and esr methods. The experimental results show that there is weak exchange interaction mediated by the bridging organic molecules between the vanadium centres. The magnitude of this interaction is more than that observed in the corresponding copper(II) dimers. The possible reason for this is discussed.     

AES investigations of the iron surface composition after laser irradiation under atmospheric conditions

The laser induced modification of iron surfaces with atmospheric species was investigated by means of Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). Different laser systems were used for irradiating iron samples in a wide range of the laser processing parameters up to small foci and ultra short pulses.A nitriding of iron connected with an oxidation of the near surface region was observed in the wavelength range between 193 nm and 10.6 m using large foci (0.1 cm²) and short pulses (10...1400ns). In case of small foci (7·10^–6cm²) with ns-pulses (50 ns) an enrichment of the iron melt with nitrogen and an advanced oxidation of the surrounding area of the laser spot were detected. When using shorter pulses (200 fs, 40 ps) no indications for a nitriding were found.     

High-resolution 13C NMR studies of solid 1,4-bis(n-butylamino)anthraquinone

High-resolution ¹³C NMR spectra of solid 1,4-bis(n-butylamino)anthraquinone are presented. In spectra measured at 22.6 MHz the effects of two short-range and two long-range residual (¹³C, ¹⁴N) dipolar couplings have been observed. Only the short-range effects are observable in the 50.3 MHz spectra. These typical asymmetric doublets allow the determination of the ¹⁴N nuclear quadrupole coupling constant (χ=e²Qq/h=?3.0 MHz), the asymmetry parameter (η=0.3) and the orientation of the electric field gradient tensor of the ¹⁴N in the molecular framework.     

Luminescence investigations of the adsorption properties of disperse Al2O3 surfaces by means of selective laser excitation

A new method for the determination of the adsorption activity of disperse materials by means of inorganic luminescent probes under selective laser excitation has been developed and tested for the investigation of the adsorption properties of disperse Al(2)O(3) surfaces. Water-uranyl complexes have been used as luminescent probes for these experiments, and the photoluminescence spectra of UO(2)(2+) molecular ions adsorbed on the disperse Al(2)O(3) surfaces were investigated. The luminescence properties of this adsorption system, as in the previously studied case of SiO(2), were determined by the type and structure of the adsorption complexes (AC) formed. Different ACs cause many (7 observed) "elementary" luminescence spectra. The water-uranyl-complex adsorption binding energies were obtained. The values of the binding energies and the electric field strength of the surface active centers support the validity of the water-uranyl model of AC and the electrostatic consideration used.     

Atomic fluorescence spectrometry with laser excitation

A laser atomic fluorescence spectrometry for the detection of trace concentrations of the elements is described. The detection limits for Pb, Fe, Na, Pt, Ir, Eu, Cu, Ag, Co and Mn in aqueous solutions obtained at present are the best ones for the rapid spectral analytical methods. The analytical potentials of the laser spectrometer are exemplified by the analysis of real samples of different chemical composition.     

Two-color two-photon excitation using femtosecond laser pulses

The use of two-color two-photon (2c2p) excitation easily extends the wavelength range of Ti:sapphire lasers to the UV, widening the scope of its applications especially in biological sciences. We report observation of 2c2p excitation fluorescence of p-terphenyl (PTP), 2-methyl-5-t-butyl-p-quaterphenyl (DMQ) and tryptophan upon excitation with 400 and 800 nm wavelengths using the second harmonic and fundamental wavelength of a mode-locked Ti:sapphire femtosecond laser. This excitation is energetically equivalent to a one-photon excitation wavelength at 266 nm. The fluorescence signal is observed only when both wavelengths are spatially and temporally overlapping. Adjustment of the relative delay of the two laser pulses renders a cross correlation curve which is in good agreement with the pulse width of our laser. The fluorescence signal is linearly dependent on the intensity of each of the two colors but quadratically on the total incident illumination power of both colors. In fluorescence microscopy, the use of a combination of intense IR and low-intensity blue light as a substitute for UV light for excitation can have numerous advantages. Additionally, the effect of differently polarized excitation photons relative to each other is demonstrated. This offers information about different transition symmetries and yields deeper insight into the two-photon excitation process.     

Basic investigations for laser microanalysis: IV. The dependence on the laser wavelength in laser ablation

The fourth harmonic wavelength at 266 nm as well as the fundamental radiation at 1.06 m of a pulsed Nd: YAG laser has been used for ablation of solid samples. Using different buffer gases and different samples, the ablated masses and plasma temperatures obtained with the two different laser wavelengths are compared. The analytical application of 266-nm laser pulses is studied by the measurement of aluminium and manganese in steel and boraxglass (Na₂B₄O₇) samples.     

Spectral and structural correlations of 1,4- and 3,4-dihydroquinazolines

Alkylation of the nucleophilic addition product of 2,4-diphenylquinazoline and organometallic derivatives produced a mixture of 1,4- and 3,4-dihydroquinazoline dreivatives. The structures were established through pmr correlations of chemical shifts of the N-CH₃ groups produced when the alkylating agent was methyl iodide. Spectra (uv, pmr) of known open-chain amidines were used to confirm the structures of the isomeric dimethyl 2,4-diphenyldihydroquinazolines. The uv spectra of 2-phenyl-3,4-dihydroquinazolines possessed an absorption maximum at 320 nm while the 1,4-dihydroanalogues had a maximum at 290 nm. Characteristic absorptions in the 1550–1650 cm^?1 region of the infrared spectra also differentiated these two groups of compounds. Removal of the 2-phenyl substituent renders these correlations less reliable.     

Trace analysis by microwave excitation of sealed samples-I: preliminary investigations

An important limitation to the sensitivity of analytical methods using atomic spectroscopy is the short residence-time of the atoms in the light-path. The possibility has been studied of sealing the samples in a quartz tube where they are forced to emit light by microwave excitation. The detection of amounts below one ng in a volume of 0.5 ml seems possible.     

Spectral shifts in the fluorescence spectrum of anthracene under the influence of laser driven shock compression

We report spectral shifts in the fluorescence emission of a solution of anthracene in benzene under the influence of laser driven shock compression. Red-shifts of up to 800 cm⁻¹ are observed in the peak of the 0–1 vibronic band of anthracene corresponding to maximum pressures of =10 kbar. These results are in agreement with literature values of spectral shifts obtained under conditions of high static pressure. Laser driven shock provides an attractive alternative to conventional shock generation schemes when used in conjunction with optical spectroscopy as a probe of molecular level changes.