Zdeněk Zelinger

Fluorescent polyurethane nanofabrics: a source of singlet oxygen and oxygen sensing.

Polyurethane (PUR) nanofabrics based on nanofibers of average diameters in the range of 250-110 nm with different meso-tetraphenylporphyrin (TPP) loading (0.01-5 wt %) were prepared by an electrospinning process. The oxygen quenching of excited states and singlet oxygen-sensitized delayed fluorescence (SODF) of TPP were studied at different oxygen pressures. We found that TPP in PUR matrix is present in monomeric state, and it is easily accessed by oxygen. Analysis of the kinetics of the TPP triplet, singlet oxygen, and SODF indicates that repopulation of TPP fluorescent state includes reaction of singlet oxygen with TPP triplets. The integrated SODF achieved more than 20% of the prompt fluorescence for nanofabric loaded with 5 wt % TPP. The dependence of SODF intensity on the TPP concentration in nanofibers is nearly quadratic.

InAsSbP/InAs lasers (2.9 μm) for spectroscopy of ammonia: low temperature investigations

Abstract The performance of the InAsSbP/InAs lasers for absorption spectroscopy of ammonia at 3370–3660 cm−1 was first shown. These continuous wave lasers based on the III–V semiconductor are alternative to a widespread utilised Pb-salt device and were first investigated in closed-cycle He-cryostat at temperatures of 32–85 K. The spectral and tuning characteristics of the laser were considered versus both heatsink temperatures and drive currents in viewpoint of applications in molecular laser spectroscopy, with best device performance being found at 45–65 K. The preliminary experiments to record spectra of the ammonia absorption with the diode were undertaken.

Detailed study of fine and hyperfine structures in rotational spectra of the free fluoroformyloxyl radical FCO2

More than 160 new hyperfine components of rotational transitions of the free fluoroformyloxyl radical FCO(2) have been measured using the Prague millimeter wave high resolution spectrometer. The frequencies of these transitions together with the previously measured data were analyzed in detail and precise values of magnetic hyperfine and fine parameters were obtained. These new parameters significantly improve the values of previously determined hyperfine parameters which were rather unreliable. The new fine and hyperfine parameters obtained in this study are compatible with those of the simultaneously electron paramagnetic resonance study. Besides that, significantly improved ground state rotational and centrifugal distortion constants of the fluoroformyloxyl radical were derived.

The Effect of the Irradiation Wavelength on the Processes Sensitized by Protoporphyrin IX Dimethyl Ester

The formation of triplet states of photosensitizers and singlet oxygen during reactions sensitized by protoporphyrin IX dimethyl ester (PPDME) and the products of its photo-oxidation in solution were studied by time-resolved spectroscopy. Irradiation with long-wavelength light (670 nm), which is absorbed by the products of photo-oxidation of PPDME, provides lower quantum yields of singlet oxygen than in sensitization with PPDME alone, which absorbs light with a wavelength of 630 nm. Spectroscopic measurements also confirmed the lower rate of sensitized photo-oxidation of bilirubin during irradiation with light with a wavelength of 670 nm.

Diode laser application for research of molecular ions

Abstract We have developed several methods of diode laser spectroscopy and have applied them for high-resolution spectroscopy and kinetic studies of molecular ions. For these purposes we have used a special high-voltage modulation technique for generation of ions in the plasma of a gas discharge. This modulator enables the studies of the formation and decay processes of ions. The modulator can also alternately switch the polarity of a high voltage and can be used for experimental measurement of velocity modulation of ions in the gas discharge. It was found that this spectrometer can be successfully used in the following regions: • -velocity modulation spectroscopy of molecular ions (ArD+, SD−), • -distinction between the velocity modulation signal of cation and anion (due to the reverse phase of both signals), • -measurement of Doppler shifts of ions (information about the velocity and mobilities of ions), • -ion kinetics (measurement of times of formation and decay of ions in the gas discharge).

Observation of HD18O, CH3OH and vibrationally-excited N2O from Odin/SMR measurements

The sub-millimetre radiometer (SMR) instrument aboard the Odin satellite launched in February 2001 is dedicated to the observation of trace gas profiles in the stratosphere and in the mesosphere, in particular water vapour and its isotopic species HDO, H2 17O and H2 18O. By averaging more than 400 000 Odin/SMR spectra over the period from November 2002 to March 2003, weak lines have been detected in the atmosphere. These weak lines have been attributed to water isotopic species HD18O, to a vibrationally-excited N2O, and to CH3OH.

Simulation of Air Pollution in a Wind Tunnel

Laser photoacoustic spectrometry and a line permeation pollution source were used in a study of the dispersion of pollution in an urban agglomerate using simulation in a wind tunnel. Applications of this measuring technique utilize the high sensitivity and broad dynamic range (3 orders of magnitude in this case) of the photoacoustic detection method. The minimum detected absorbance in the photoacoustic detection method employed in this work was at the level of ≅4.3 × 10-6 (≅ 8 μg/m3 CH3OH). The effectiveness and flexibility of the permeation method of generation of various concentrations of gases was verified for simulation of emission pollution sources in a wind tunnel. The line permeation pollution source developed in this work, with a concentration flux of (8.3 × 10-5 ± 2 × 10-6) g/s at 20 °C, generated a concentration level in the model used from a background value of 80–90 μg/m3 up to values of ≅ 1000 μg/m3 of methanol. A simple model street canyon together with the pollution source was employed to carry out a number of measurements of spatial profiles. The dispersion of the pollutant was studied at the bottom and on the walls of the street canyon together with the concentration variation with changes in the wind speed. The laboratory model was used to demonstrate the differences in ventilation of the street canyon. Using the laser sheet visualisation method, a video technique was applied to show the real flow in the street canyon for various reference velocities. Spatial measurement of the concentration distribution inside the street canyon was carried out on the model with reference velocity of 1.5 m/s. The dependence of the concentration field on the Reynolds number was estimated from the measurements of concentrations in the vicinity of the line permeation source.

Photophysical properties of CdSe quantum dot self-assemblies with zinc phthalocyanines and azaphthalocyanines

The formation of self-assemblies between CdSe quantum dots (QDs) and Zn phthalocyanines (Pc) and azaphthalocyanines (AzaPc) bearing alkylsulfanyl substituents and the photophysical properties of these assemblies were studied using both steady-state and time-resolved luminescence/absorption spectroscopy. The formation of the self-assemblies was accompanied by a blue shift of the Q band of the dyes and by a quenching of the CdSe QDs luminescence. The largest spectral shift of the Q-band was approximately 7 nm and was observed for pentan-3-ylsulfanyl-functionalised phthalocyanine (). Assuming a 1 : 1 stoichiometry, the calculated binding constant was 4 × 10(4) M(-1). Pc substituted with the bulky tert-butylsulfanyl groups (1) exhibited a smaller shift of the Q band. The quenching of the CdSe QDs luminescence by 1 was more effective than that observed for 3. The results indicated that the luminescence quenching may be due to a photoinduced charge transfer between 1 or 3 and the CdSe QDs. In contrast, the AzaPc (2) with the same substituents as 1 had little effect on the QDs luminescence. For all cases, we found an inefficient resonance energy transfer between the attached dyes and the CdSe QD. The formation of the self-assemblies had negligible effects on the photogeneration of the singlet oxygen, O2((1)Δg), that was fully controlled only by the absorption of the light by the macrocycles.

Effect of temperature on photophysical properties of polymeric nanofiber materials with porphyrin photosensitizers.

Electrospun nanofibers possess large surface to volume ratios, high porosity, and good mechanical properties that are necessary for biological applications. We prepared different types of photoactive polymeric nanofiber materials with encapsulated or externally bound porphyrin photosensitizers. The kinetics of formation and the decay of both singlet oxygen O2((1)Δg) and porphyrin triplet states that are generated by irradiation of nanofiber materials in an air atmosphere or in an air-saturated aqueous solution were measured and evaluated by luminescence and transient absorption spectroscopy in the temperature range between 5 and 60 °C. We found shortening of the O2((1)Δg) lifetime and a significant increase in singlet oxygen-sensitized delayed fluorescence at higher temperatures. These photophysical data show an increase in the diffusion coefficient for O2((1)Δg) with temperature, and they are consistent with a stronger antibacterial effect of the nanofiber material on Escherichia coli at higher temperature.

Dispersion of Light and Heavy Pollutants in Urban Scale Models: CO2 Laser Photoacoustic Studies

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO2 laser photoacoustic spectroscopy in the region of the atmospheric window (9–10 μm). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.