The role of cellulose acetate as a matrix for aggregation of pseudoisocyanine iodide: absorption and emission studies

Films of pseudoisocyanine iodide in a cellulose acetate matrix were prepared by spin coating and characterized by UV/Vis absorption and fluorescence spectroscopies. The comparison with self-supported films of the same dye enabled analysing the role of the matrix in the aggregation of pseudoisocyanine iodide ([PIC]I). It was proved that cellulose acetate is a suitable support for [PIC]I J-aggregates, which form during spinning, as shown by a very sharp J-band in the absorption spectra. This indicates a perfect coherence between stacked monomers in the supported J-aggregates. It was possible to individualize the emission spectrum of [PIC]I J-aggregates in cellulose acetate, by decomposition of the steady-state fluorescence spectra of the films. The dependence on the excitation wavelength of the relative emission intensities of monomers and J-aggregates, for lambda(em) = 587 nm, lead to confirm that the latter species have an absorption maximum at approximately 500 nm in cellulose acetate. Finally, polarised absorption spectra of films obtained by the vertical spin coating technique showed that cellulose acetate allows a partial orientation of J-aggregates.     

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.     

Relaxation processes of singlet excited state of 3,3′-diethyloxadicarbocyanine iodide (DODCI) photoisomer

Fluorescence induced by laser excitation was used in the study of the deactivation processes of excited states of both isomeric forms of 3,3′-diethyloxadicarbocyanine iodide (DODCI). Connection between excited states was analyzed by a two-step excitation method, and no evidence of a direct connection between them was found at low concentrations. This technique allowed us to obtain a normal fluorescence free photoisomer spectrum for the first time. Using cw excitation, saturated fluorescence spectra were interpreted on the basis of a photochromic system involving normal and photoisomer ground states and excited singlet states. A similar one-dimensional barrier picture is obtained, comparing the results with the direct photoisomerization process.     

Molekülabsorptionsspektrometrie bei elektrothermischer verdampfung in einer graphitrohrküvette: IV. Bestimmung von jodidspuren durch tlj-molekülabsorption

Molecular absorption, spectrometry with electrothermal volatilization in a graphite tube. Part 5. Determination of iodide traces by molecular absorption of TlI.The molecular absorption of thermally stable TlI, generated by evaporation in a normal graphite cuvette, is suitable for the determination of traces of iodide in small samples. Optimal conditions are described, and interferences are discussed. The reciprocal sensitivities relative to 0.01 absorbance are 80 ng of iodide at 202 nm and 160 ng of ng ^J- (380.4 nm).     

TRIPLET YIELD OF MEROCYANINE 540 IN WATER IS WAVELENGTH DEPENDENT

Monomers and aggregates of Merocyanine 540 (MC540) in water are able to photoisomerize. The shape of the photoisomer absorption spectrum is very similar to that of the ground state. Triplet state of MC540 in water has been produced by energy transfer from triplet anthracene and displays a broad absorption spectrum between 600 and 700 nm. The triplet state may also be produced by direct excitation of MC540 with UV light. However, when the dye is excited by visible light, no triplet state absorbance in the red could be detected so that the triplet yield of MC540 in water seems to be excitation wavelength dependent.     

Transient absorptions in a polymethine laser dye

Transient absorptions in HITC are investigated in the range 650-950 nm by a conventional flash photolysis technique and “picosecond” spectroscopy with a train of 6 to 7 pulses. This study gives evidence for S₁-S_n absorption, photoisomer and triplet generation. The comparison between experimental data and computer solutions allows the determination of the rate constants of these processes and molar extinction coefficients of the absorption spectra. Taking into account these results, we discuss the limitations of the performances of the flashlamp excited HITC dye laser.     

Determination of iodine via the spectrum of barium mono-iodide using high-resolution continuum source molecular absorption spectrometry in a graphite furnace

Molecular absorption spectra of the diatomic molecules AlI, GaI, InI, TlI, MgI, CaI, SrI and BaI, generated in a graphite furnace, were studied using a high-resolution echelle spectrometer with the aim of finding a simple, reliable and sensitive analytical method for the determination of iodine. Among them, the barium mono-iodide (BaI) was found to have the strongest absorption bands around 538 nm and 560 nm, each of them consisting of a series of well-resolved rotational lines with half-widths of about 40–50 pm. The strongest BaI line, the band head at 538.308 nm has been evaluated systematically for its analytical use for the determination of iodine. High concentrations of hydrochloric acid (or chloride), hydrofluoric acid (or fluoride), iron, potassium and sodium resulted in significant reduction of the BaI molecular absorption. Apart from this, no other serious spectral or non-spectral interference has been observed. Different chemical forms of iodine, such as iodide, iodate and organically bound iodine produced identical BaI absorption sensitivity. The detection limit for iodine was 600 pg, and the calibration curve was linear up to 250 ng iodine. Two real samples with different chemical forms of iodine were analyzed using the proposed method. One sample was an iodide pill with a specified iodide content of 200 mg, the other one was a thyroid hormone pill with a specified content of 63.5 mg. The results were in good or satisfactory agreement with those of independent methods, the potentiometric titration and the inductively coupled plasma time-of-flight mass spectrometry (ICP-ToF-MS); the deviations were 2% and 8% for the iodide and the thyroid hormone sample, respectively. The relative standard deviation of the analytical results (n = 3) was below 2%.     

Direct determination of nanogram amounts of iodine by atomic-absorption spectroscopy using a graphite-tube atomizer

The direct determination of iodine by AAS at its 183.0 and 178.2 nm resonance lines by using a small graphite-tube atomizer, electrodeless discharge-lamp source and vacuum monochromator is described. Optimum conditions for the determination of iodine have been established; similar sensitivity is obtained when iodide or iodate samples are examined. With 10 mul aqueous samples sensitivities (for 1% absorption) of 4 x 10(-10) g and 2 x 10(-10) g of I were obtained at 183.0 and 178.2 nm respectively; a detection limit of 2 x 10(-10) g was observed at both lines. Non-specific molecular absorption from common inorganic salts causes interference with the determination; the iodine non-resonance line at 184.4 nm may be employed to correct for this interference when moderate amounts of common salts are present.     

Spectroscopic behavior of 1,1′-diethyl-2,2′-dicarbocyanine iodide in ethanol/water solutions with high ionic strength

Absorption spectra of 1,1′-diethyl-2,2′-dicarbocyanine iodide (DDI) have been obtained in ethanol/water mixtures. Increase of ionic strength obtained by addition of salts (e.g. NaCl) to the solvent mixture containing 10% of H₂O and 90% of EtOH leads to appearance of a new absorption band at 849 nm. Intensity of this band increases with salt concentration which suggests that this spectral feature is related to a DDI aggregate. However, no emission has been observed with excitation at 850 nm indicating that this feature does not correspond to a J-type aggregate. Addition of NaCl to DDI solutions possessing the EtOH/H₂O (v:v) ratio different from 1:9 does not induce appearance of the new absorption band.     

The Faraday effect for sodium anion in solution

The Faraday effect for sodium dissolved in EDA indicates a magentic moment of about one Bohr magneton for the excited state involved in the 650 nm absorption. Comparison with results for iodide ion suggest a structure for the 650 nm band. A simple connection between ellipticity and derivative of absorption is pointed out and used in analyzing the data.     

纳米AgBr乳剂的制备及其紫外吸收光谱的研究

通常人们把粒径1~100 nm之间的金属、半导体、氧化物及各种化合物的粒子或者粒子的集合体称为纳米粒子。近年来的纳米粒子化学和物理的迅速发展已经证实:随着原子或分子簇尺寸的减小,表面原子的比例逐渐增大,粒子表现了与块状材料不同的特性,其粒子显示出以“量子尺寸效应”为主的特点,特性表现出种种异常^[1,2]。     

Fast and simple method for determination of iodide in human urine, serum, sea water, and cooking salt by capillary zone electrophoresis

For the determination of iodide in urine, where 80-90% of consumed iodine is excreted, a fast, simple, and sensitive method of capillary zone electrophoresis was elaborated and tested also for additional complex matrices such as human serum, cooking salt, and seawater. Several approaches were examined for the separation of iodide from other macro- and microcomponents in the tested matrices, and the best results were obtained when host-guest interaction with alpha-cyclodextrin or ion-pairing with polyethylenimine was employed. In both cases comparable resolution and sensitivity were reached. Due to the relatively high price of cyclodextrin only the method with polyethylenimine was further optimized and a simple procedure enabling the determination of iodide in untreated human urine, serum, cooking salt, and seawater was elaborated. The samples were injected for 20 s at 0.5 psi (3.45 kPa) into a fused-silica capillary (0.18 mm ID, 50 cm effective length) coated with polyacrylamide (electroosmotic flow < 2 x 10(-9) m(2)V(-1)s(-1)) and filled with the optimized background electrolyte composed of 20 mM KH(2)PO(4) and 0.7% m/v polyethylenimine. For detection, UV absorption at 200 and 230 nm was measured. Concentration limits of detection reached at 230 nm were for human urine 0.14 microM, for human serum 0.17 microM, for seawater 0.17 microM, and for cooking salt 89 nM. Relative standard deviations of iodide peak area and height in all matrices ranged within 0.93 to 4.19%.     

Zeeman effect of the S1 ← S0 transition of the two tautomeric forms of chlorin: a study by photochemical hole burning in an n-hexane host

Zeeman experiments are reported on the S₁ ← S₀ O-O transitions of chlorin (7,8-dihydroporphin) and its photoisomer in an n-hexane crystal by photochemical hole burning at 4.2 K. The holes shift with a quadratic field dependence of -39.0 MHz/T² (chlorin) and ?245.3 MHz/T² (photoisomer). For chlorin A = ¦<S₁¦L_z¦S₂ > ¦=4.5. Single-site absorption and fluo spectra are reported. PPP calculations were performed.     

Tuning of the properties of rhodopsin-based molecular switches

The modification of relevant chemical properties of rhodopsin-based molecular photoswitches is presented. We show how both the substituents present and the nitrogen atom quaternization are capable to change the wavelength of absorption and the thermal stability of the photoisomer. Adjusting these properties, the molecular switches could be turned into useful compounds for solar energy storage devices.     

Picosecond kinetics and transient spectra of pseudoisocyanine monomers and J-aggregates in aqueous solution

Bleaching of monomer and J-aggregate bands of pseudoisocyanine was observed using tunable excitation wavelengths. Both bleached bands decrease with (15 ± 3) ps. A residual J-band bleaching exists up to 1 ns. A new transient absorption in superposition with the J-band was round to consist of two bands with different time behaviour.     

High-temperature thermal decomposition of benzyl radicals

The thermal decomposition of the benzyl radical was studied in shock tube experiments using ultraviolet laser absorption at 266 nm for detection of benzyl. Test gas mixtures of 50 and 100 ppm of benzyl iodide dilute in argon were heated in reflected shock waves to temperatures ranging from 1430 to 1730 K at total pressures around 1.5 bar. The temporal behavior of the 266 nm absorption allowed for determination of the benzyl absorption cross-section at 266 nm and the rate coefficient for benzyl decomposition, C6H5CH2 --> C7H6 + H. The rate coefficient for benzyl decomposition at 1.5 bar can be described using a two-parameter Arrhenius expression by k1(T) = 8.20 x 10(14) exp(-40 600 K/T) [s(-1)], and the benzyl absorption cross-section at 266 nm was determined to be sigma(benzyl) = 1.9 x 10(-17) cm2 molecule(-1) with no discernible temperature dependence over the temperature range of the experiments.     

Photoinduced molecular rearrangements. Some comments on the ring‐photoisomerization of 1,2,4‐oxadiazoles into 1,3,4‐oxadiazoles

The ring‐photoisomerization of 3‐amino‐ and 3‐methylamino‐5‐phenyl‐1,2,4‐oxadiazoles into the corresponding 2‐amino‐ and 2‐methylamino‐5‐phenyl‐1,3,4‐oxadiazoles has been reinvestigated by examining the effect of a base on the photoreaction. On irradiating at λ = 254 nm in methanol, yields of the ring‐photoisomers were found to be significantly enhanced by the addition of triethylamine (TEA) in the photoreaction medium. By contrast, irradiation of the 3‐amino‐5‐phenyloxadiazole in acetonitrile containing TEA gave an almost complete photoreduction into benzoylguanidine, while few percent of the ring photoisomer were detected. Furthermore, the pyrene‐sensitized photolysis of 3‐amino‐5‐phenyloxadiazole in acetonitrile containing triethylamine also gave benzoylguanidine but no traces of the ring photoisomer.     

Chemical enhancement method for the determination of mercury by spectrophotometry after iodide extraction

A selective and sensitive spectrophotometric method for the determination of 0.08-2.5 ppb of mercury(II) is described. Mercury is extracted as tetraiodomercury(II)-Cd-phenanthroline ion-pair into benzene and selectively stripped into EDTA. The iodide associated with mercury present in the stripping is oxidized to iodate and then treated with excess iodide to give iodine. The iodine formed is extracted into benzene and equilibrated with iodate in acidic medium in the presence of chloride and Rhodamine 6G for the formation of ICI(-)(2) species and its extraction as ion-pair with Rhodamine 6G. Determination is completed by measuring the absorption of the extract at 535 nm. The coefficient of variation is 1.5% for 10 determinations of 200 ng of mercury. The method has been applied to establish the mercury content of natural waters and chloralkali plant effluent.     

Spectrophotometric determination of palladium by reaction with tin(II) in binary halide mixtures

The coloured complexes produced in the systems Pd(II): Sn(II):X:X', where X and X' are different halide ions, have been studied. In bromide/iodide mixtures, palladium(II) reacts with tin(II) species in acidic ethanol media to form a deep purple complex with maximum absorption at 555 nm. This is the basis of a rapid and sensitive spectrophotometric method for the determination of palladium. The complex is stable in the absence of air, but water interferes and must not be present in amounts more than 15% of the total volume of the ethanolic mixture.     

Butterfly diradical intermediates in photochemical reactions of Fe2(CO)6(mu-S2)

Photolysis of the tetrahedrane Fe2(CO)6(mu-S2) at 450 +/- 35 nm in a Nujol matrix at low temperatures gives an isomer characterized by its nu(CO) infrared frequencies. Comparison of these experimental frequencies with those calculated by density functional theory using the BP86 functional indicates this photoisomer to be the butterfly singlet diradical Fe2(CO)6S2 isomer in which the S-S bond of the tetrahedrane is broken but the Fe-Fe bond is retained. Photolysis at higher energies (420-280 nm) results in CO loss from this singlet butterfly diradical as indicated again by comparison of the experimental infrared nu(CO) frequencies with those calculated for an Fe2(CO)5S2 isomer of this type.