Organic LEDs Based on Bis(8-hydroxyquinoline) Zinc Derivatives with a Styryl Group

For the first time, organic light-emitting diodes (OLEDs) based on bis(8-hydroxyquinoline) zinc with a styryl group (ZnStq) dispersed in poly(N-vinylcarbazole) matrix (ZnStq_R:PVK, where R = H, Cl, OCH3) were fabricated. The ZnStq_R:PVK films made via the spin-coating method were used as the active layer in these devices. The produced OLEDs showed strong electroluminescence with yellow emissions at 590, 587 and 578 nm for the ZnStq_H:PVK, ZnStq_Cl:PVK and ZnStq_OCH3:PVK, respectively. For all the studied thin films, the main photoluminescence emission bands were observed between 565 and 571 nm. The OLED with the ZnStq_OCH3:PVK layer with a narrow electroluminescence spectrum was found to have sufficient color purity to produce ultra-high-resolution displays with reduced power consumption (full width at half maximum of 59 nm, maximum brightness of 2244 cd/m2 and maximum current efficiency of 1.24 cd/A, with a turn-on voltage of 6.94 V and a threshold voltage of 7.35 V). To characterize the photophysical properties of the active layer, the ZnStq_R:PVK layers samples were additionally deposited on glass and silicon substrates. We found that the obtained results predestine ZnStq_R:PVK layers for use in the lighting industry in the future.

Photoinduced charge transfer in push-pull pyrazoline-based chromophores - Relationship between molecular structure and photophysical, photovoltaic properties

The manuscript describes the effect of molecular structure on the photophysical and photovoltaic properties of the pyrazoline-based donor-branched-π-system-acceptor compounds decorated with two end groups: phenyl or thiophene. Although the absorption to the first singlet excited state is strongly allowed, the emission quantum yield is low in all studied solvents. This behaviour was explained by the existence of two non-radiative deactivation channels: the back electron transfer process, especially operated in polar solvents, and internal conversion realized as the rotation of flexible rotors (cyano, keto phenyl or thiophene). The feasibility of the photoinduced electron transfer process was corroborated by electrochemical, spectroelectrochemical measurements as well as DFT calculations. DFT calculations also support the existence of multiple conformations in the ground state, which differ from one another in terms of charge distribution and the values of ground state dipole moment. Finally, the mechanism of the singlet excited state deactivation of the studied compounds was determined by ultrafast pump-probe measurements. Our studies revealed that charge/electron transfer process may undergo over carbonyl bridge, included in branched π-system. Moreover, the thiophene decorated pyrazoline is characterized by a better photovoltaic power conversion efficiency, while the phenyl-ended pyrazoline can be applied as a viscosity sensor.

Zinc Oxide Films Fabricated via Sol-Gel Method and Dip-Coating Technique-Effect of Sol Aging on Optical Properties, Morphology and Photocatalytic Activity

Zinc oxide layers on soda-lime glass substrates were fabricated using the sol-gel method and the dip-coating technique. Zinc acetate dihydrate was applied as the precursor, while diethanolamine as the stabilizing agent. This study aimed to determine what effect has the duration of the sol aging process on the properties of fabricated ZnO films. Investigations were carried out with the sol that was aged during the period from 2 to 64 days. The sol was studied using the dynamic light scattering method to determine its distribution of molecule size. The properties of ZnO layers were studied using the following methods: scanning electron microscopy, atomic force microscopy, transmission and reflection spectroscopy in the UV-Vis range, and the goniometric method for determination of the water contact angle. Furthermore, photocatalytic properties of ZnO layers were studied by the observation and quantification of the methylene blue dye degradation in an aqueous solution under UV illumination. Our studies showed that ZnO layers have grain structure, and their physical-chemical properties depend on the duration of aging. The strongest photocatalytic activity was observed for layers produced from the sol that was aged over 30 days. These layers have also the greatest porosity (37.1%) and the largest water contact angle (68.53°). Our studies have also shown that there are two absorption bands in studied ZnO layers, and values of optical energy band gaps determined from positions of maxima in reflectance characteristics are equal to those determined using the Tauc method. Optical energy band gaps of the ZnO layer fabricated from the sol aged over 30 days are E_g^I = 4.485 eV and E_g^II = 3.300 eV for the first and second bands, respectively. This layer also showed the highest photocatalytic activity, causing the pollution to degrade 79.5% after 120 min of UV irradiation. We believe that ZnO layers presented here, thanks to their attractive photocatalytic properties, may find application in environmental protection for the degradation of organic pollutants.

Influence of P3HT:PCBM Ratio on Thermal and Transport Properties of Bulk Heterojunction Solar Cells

The influence of P3HT:PCBM ratio on thermal and transport properties of solar cells were determined by photothermal beam deflection spectrometry, which is advantageous tool for non-destructively study of bulk heterojunction layers of organic solar cells. P3HT:PCBM layers of different P3HT:PCBM ratios were deposited on top of PEDOT:PSS/ITO layers which were included in organic bulk-heterojunction solar cells. The thermal diffusivity, energy gap and charge carrier lifetime were measured at different illumination conditions and with a different P3HT:PCBM ratios. As expected, it was found that the energy band gap depends on the P3HT:PCBM ratio. Thermal diffusivity is decreasing, while charge carrier lifetime is increasing with PCBM concentration. Energy band gap was found to be independent on illumination intensity, while thermal diffusivity was increasing and carrier lifetime was decreasing with illumination intensity. The carrier lifetime exhibits qualitatively similar dependence on the PCBM concentration when compared to the open-circuit voltage of operating solar cells under AM1.5 illumination. BDS and standard I-V measurement yielded comparable results arguing that the former is suitable for characterization of organic solar cells.

Sol-Gel Derived Silica-Titania Waveguide Films for Applications in Evanescent Wave Sensors-Comprehensive Study

Composite silica-titania waveguide films of refractive index ca. 1.8 are fabricated on glass substrates using a sol-gel method and dip-coating technique. Tetraethyl orthosilicate and tetraethyl orthotitanate with molar ratio 1:1 are precursors. Fabricated waveguides are annealed at 500 °C for 60 min. Their optical properties are studied using ellipsometry and UV-Vis spectrophotometry. Optical losses are determined using the streak method. The material structure and chemical composition, of the silica-titania films are analyzed using transmission electron microscopy (TEM) and electron dispersive spectroscopy (EDS), respectively. The surface morphology was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods. The results presented in this work show that the waveguide films are amorphous, and their parameters are stable for over a 13 years. The optical losses depend on their thickness and light polarization. Their lowest values are less than 0.06 dB cm^-1. The paper presents the results of theoretical analysis of scattering losses on nanocrystals and pores in the bulk and interfaces of the waveguide film. These results combined with experimental data clearly indicate that light scattering at the interface to a glass substrate is the main source of optical losses. Presented waveguide films are suitable for application in evanescent wave sensors.

1H-Pyrazolo[3,4-b]quinolines: Synthesis and Properties over 100 Years of Research

This paper summarises a little over 100 years of research on the synthesis and the photophysical and biological properties of 1H-pyrazolo[3,4-b]quinolines that was published in the years 1911–2021. The main methods of synthesis are described, which include Friedländer condensation, synthesis from anthranilic acid derivatives, multicomponent synthesis and others. The use of this class of compounds as potential fluorescent sensors and biologically active compounds is shown. This review intends to summarize the abovementioned aspects of 1H-pyrazolo[3,4-b]quinoline chemistry. Some of the results that are presented in this publication come from the laboratories of the authors of this review.

Mechanical and Combustion Properties of Agglomerates of Wood of Popular Eastern European Species

The objective of the reported project was to produce wood agglomerates from popular East European species to determine their strength and combustion properties. Closed-die pellets were produced from sawdust of six types of wood common on the East European market: pine, willow, oak, poplar, birch, and beech. The properties of pellets, determined by the type of wood, were influenced by the compaction pressure and the moisture content of the sawdust. The highest average pellet density was obtained for oak sawdust, while the lowest density was obtained for poplar pellets. Expansion of pellets after removing from the die was found to be dependent on the wood species, and as expected, on compaction pressure. The pellet expansion increased after 2 h of conditioning in the laboratory and with an increase in moisture content. The highest and the smallest strength were obtained for oak pellets and for birch sawdust, respectively. The strength of the pellets increased by more than 100% with an increase in the compaction pressure from 60 MPa to 120 MPa. The average strength decreased by 65% with increasing moisture content. For all tested materials, drop resistance remained at a high level, acceptable in industrial practice. The highest calorific value of 18.97 MJ/kg was obtained for pine pellets. The highest ash value of 1.52% was obtained for willow pellets and the lowest value of 0.32% for pine pellets.

Friction and Shear Properties of Pine Biomass and Pellets

Knowledge on the mechanical properties of granular biomass is important for the design and efficient operation of equipment used for handling, storage, and processing. Their mechanical properties are used as a measure of material quality. In this study, the mechanical properties of granular biomass obtained from pines (sawdust, shavings, long shavings, and pellets) were determined under a moisture content range of 10–50%. The coefficient of sliding friction µ of four construction materials was determined using a 210-mm-diameter direct shear tester (Jenike’s shear box). To measure the shear resistance of the biomass materials (represented as torque T), a prototype vane tester was constructed. The characteristics of shear resistance with respect to time T(t) were determined for material samples under normal pressure p ranging from 5 to 30 kPa and a vane rotation rate of 3 rpm. Measurements were performed for five geometries of the rotor, reflecting typical deformation conditions encountered in the processing of granular biomass. The coefficient of sliding friction was found to be affected by the type of material, moisture content, and normal compressive pressure. Depending on the biomass material, the highest µ, which ranged from 0.50 to 0.62, was obtained for black steel, whereas the lowest µ, which ranged from 0.27 to 0.52, was obtained for aluminum. The lowest coefficient of sliding friction was observed for dry materials and high normal pressure. The torque T was observed to be affected by the rotor shape, material, normal pressure, and moisture content. The parameters presented provide information useful for the design of transport equipment and processing of granular wood biomass.

The Influence of Osmotic Dehydration Conditions on Drying Kinetics and Total Carotenoid Content of Kiwiberry (Actinidia Arguta)

Kiwiberries (Actinidia arguta var. Geneva) were osmotically dehydrated in sucrose, xylitol and maltitol 60 % water solutions at 30 and 50 °C. After pre-treatment, the samples were dried using convective method at 70 °C until fruits have reached a dimensionless moisture ratio (MR) of 0.02. Osmotic pre-treatment significantly improved drying kinetics during the first stage of the process. All the pre-treated samples reached water activity level (aw) less than 0.6 after 7 h of drying. When maltitol or xylitol was used as an osmotic agent at 30 °C, the time required for drying was reduced by 23 and 32 %, respectively. In turn, dehydration performed at 50 °C had no positive effect on the drying kinetics. The shortest drying time was obtained for the samples dehydrated in xylitol at 30 °C. In the case of these samples target MR was reached after 542 min whereas in the case of untreated samples drying lasted 810 min. The highest retention of carotenoid was observed for the samples osmotically pre-treated in maltitol solution at 30 °C and sucrose solution at 50 °C.

The effect of vegetable and spice addition on the acrylamide content and antioxidant activity of innovative cereal products

The aim of the work was to assess the impact of vegetable and spice addition on the acrylamide content and antioxidant activity of extruded cereal crisps. The foods were based on grain ingredients, such as brown rice, whole grain flour, wheat bran, with different vegetables. Products from one group contained green vegetables, such as broccoli and zucchini; garlic was included as a flavour additive (0.75-1.50%). The second group of crisps consisted of similar cereal ingredients with pumpkin and cinnamon; additionally ginger was included as a flavour additive (0.75-1.50%). The results indicate that the production of a new, innovative product with appropriate nutritional value and acceptable quality is a complex process. The production process significantly changed the nutritional value of the product. The content of acrylamide in zucchini and broccoli crisps was relatively low; ranging from 78 to 86 μg/kg of product. The addition of garlic did not significantly affect the acrylamide content in the final product. For cereal-pumpkin crisps, the acrylamide content was 7 times higher in comparison with zucchini and broccoli products. The acrylamide content in pumpkin and ginger crisps exceeded the benchmark level. The antioxidant activity of the pumpkin product was significantly higher (p < 0.05) than for crisps with green vegetables.

Mass Transfer in Osmotic Dehydration of Kiwiberry: Experimental and Mathematical Modelling Studies

The aim of this study was to analyze the impact of osmotic solutions and temperature on the osmotic dehydration (OD) of two cultivars of kiwiberry. OD was carried out in sucrose, xylitol and maltitol solutions at 30 °C and 50 °C, respectively. The process of osmotic dehydration was described by the means of water loss (WL), solid gain (SG), weight reduction (WR), and water content changes. Moreover, dehydration was described by mathematical models often used in the literature. The highest WL, WR and SG values were observed for samples treated by xylitol and maltitol at 50 °C. The statistical analysis of the mathematical modelling of the process showed that in most cases, the Peleg’s equation exhibits better fitting for the experimental data.

Diastase Activity Retention and Physical Properties of Honey/Arabic Gum Mixtures After Spray Drying and Storage

The effect of heat treatment (75 °C) and spray drying with the addition of Arabic gum (inlet/outlet air temperature 180/75 °C), on the diastase activity of multifloral honey (MH) and rape honey (RH) was investigated. The physical properties of the powders (particle size and morphology, water content and activity, bulk loose and tapped density, angle of repose, hygroscopicity) directly after drying and after 12 weeks of storage were studied. During heat treatment, diastase activity decreased gradually, to decline below limit values after 180 min. Diastase activity in the powders was lower than in fresh honeys, but it was concluded that temperature was not the only factor affecting this decrease. Powders were characterized by low water content and medium flowability, which was improved after storage due to particle size increase. Diastase activity in powders was stable during storage.

Effect of Processing Conditions on Microstructure and Pasting Properties of Extrusion-Cooked Starches

The aim of the work was to investigate the effect of extrusion-cooking process conditions on the structure and pasting properties of starch extrudates. In addition, the extrudates structure was observed using scanning electron microscopy (SEM) and confocal laser microscopy (CSLM). Wheat, corn and potato starch were extrusion-cooked with different process parameters (moisture content, screw speed, process temperature) in a single screw extruder. Results showed influence of the process parameters on extruded starches pasting properties. Viscosity measurements indicated that water content during starch extrusion is more important than process temperature. The extrudates structure observed with scanning electron and confocal laser microscopes showed that the main effect of extrusion-cooking was loss of the crystalline structure of the starch and the formation of a cellular structure of the extrudates. In extrudates processed at higher starch moisture content reduced the quantity and diameters of created cells was observed.

Spectral kinetics of fluorescence spectra of fluoroderivatives of pyrazoloquinoline in different polymer matrices

Three fluoro-substituted pyrazoloquinoline derivatives have been placed in polymer matrices: polycarbonate, poly(methyl methacrylate) and polystyrene. Absorption, excitation and time-resolved fluorescence spectra have been recorded and luminescence lifetime of the optically active composites has been determined. Influence of the dielectric environment the optical properties of the chromophores are discussed. Experimental data and conclusions are supported with (TD)DFT calculations.

IR laser induced spectral kinetics of AgGaGe3Se8:Cu chalcogenide crystals

The possibility to operate by optical spectra near the absorption edge gap was discovered for the AgGaGe3Se8:Cu semiconducting chalcogenide crystals under influence of microsecond CO2 laser with pulse energy 60 mJ operating at wavelength 10.6 μm. An occurrence of substantial photoinduced optical density was observed at wavelengths in the spectral range of 610-620 nm. Introducing of Cu ions leads to substantial spectral asymmetry in the observed spectra. The process achieves its maximum value after the 80-120 s of CO2 laser treatment and relaxes with almost irreversible changes after the same time. The contribution of thermo heating did not exceed 5-6%. Only the irreversible changes of the sample's surface topography were observed during the CO2 laser treatment, which do not influence the treatment. So the surface states do not play a principal role and the effect is prevailingly originated from the. The observed effect may be used for control of the CO2 laser power density.

Novel dipyrazolopyridine derivatives as deep blue emitters for polymer based organic light emitting diodes

Paper reports synthesis and spectroscopic properties of four newly synthesized dipyrazolo[3,4-b; 3',4'-e]pyridine (DPP) derivatives. The spectroscopic studies are supplemented by quantum-chemical calculations using DFT/TDDFT/PCM method at the B3LYP/6-31+G(d,p) level of theory. The optical absorption and fluorescence emission processes appear to be weakly dependent on attached side phenyl and/or methyl groups exhibiting in cyclohexane solution the first absorption band (00' transition) in the region of 386-401 nm and the fluorescence band (0'0 transition) in the range of 412-425 nm. The electroluminescence devices (OLEDs) with an active PVK layer doped by DPP dyes have been designed. All the devices exhibit deep blue electroluminescence with the emission maximum being rather weakly dependent on the type of the fluorescent dopant. The obtained results demonstrate that a series of newly synthesized DPP dyes may be considered as perspective blue fluorescent emitters for electroluminescent applications.

Optical operation by chromophores featuring 4,5-dicyanoimidazole embedded within poly(methyl methacrylate) matrices

We have studied photoinduced absorption, birefringence, and optical second-harmonic generation in poly(methyl methacrylate) (PMMA) films doped by organic chromophores featuring 4,5-dicyanoimidazole in the weight content equal to 5%. The chromophores indicated as IM1-IM6 were synthesized from 2-bromo-1-methylimidazole-4,5-dicarbonitrile by either nucleophilic substitution or Suzuki-Miyaura cross-coupling reaction. The samples were obtained as films of several micrometers thickness by the spin-coating method on a quartz substrate. Measurements of the optically induced birefringence were done by the Senarmont method at wavelength 1150 nm, and photoinduced absorption was studied in the spectral range 250-700 nm under optical treatment by 300 mW cw 532 nm laser. Photoinduced optical effects were studied by bicolor 1064 and 532 nm coherent laser pulses. The maximal changes were observed for the ratio between fundamental and writing beam intensities equal to about 7:1. To interpret the observed experimental measurements, theoretical simulations of photoinduced optical properties were performed by quantum chemical computational methods.

Spectroscopy of fluoro derivatives of 1H-pyrazolo[3,4-b]quinoline in different solvents

Theoretical simulations of UV-vis spectra for organic chromophores: 3-(4-fluorophenyl)-1,4-diphenyl-, 1-(4-fluorophenyl)-3,4-diphenyl- and 4-(4-fluorophenyl)-1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline. Density Functional Theory 6-31G calculations were performed. The molecular geometry and UV-vis spectra were simulated with the time-dependent DFT calculations. Influence of number of occupied and excited states on the behavior of the spectra is explored. To further improve the calculations a Polarizable Continuum Model (PCM) was employed to simulate the influence of solvent polarity. It was used in both geometry optimization and spectra simulation. An attempt to find a correlation between the values of dipole moments and the spectral shifts was performed. The results were compared with experiment.

Influence of chromophore dipole moments in parameters of organic light emitting devices based on phenyl and methyl modified pyrazoloquinoline

Absorption, photo- and electroluminescence spectra of some trityl substituted 1H-pyrazolo[3,4-b]quinolines derivatives (methyl- and phenyl substituted) and fabrication of the single layered organic light emitting diodes are reported. The bulky trityl substituent was introduced to prevent aggregation and crystallization of the dopant in polymer matrix. Role of ground state dipole moments in the observed red Stokes shift, electroluminescent features and photocarrier transport is explored. The maximally achieved brightness about 50Cd/m(2) is observed in the spectral range extending from 443nm up to 462nm. The voltage threshold was varied from 7.8V up to 10V. The brightness-current dependences show an existence of at least two types of carrier injections.

Optical absorption of bisphenol A based pyrazoloquinoline dimers

The paper presents the measured absorption spectra for several newly synthesized derivatives of bisphenol A based pyrazoloquinoline dimers (BAPQD). The experimental results are compared with quantum chemical calculations performed by semiempirical method AM1 and PM3. Molecular mechanic analysis shows that BAPQD dyes possess by a large number of equilibrium molecular conformations with similar total energies and small energy barriers between these states; thus at room temperature (T=300 K) the molecular dynamics exhibits slow temporal evolution passing a large number of intermediate slightly non-equilibrium conformational states. For this reason the semiempirical quantum chemical methods have been combined with the molecular dynamics simulations. The semiempirical PM3 method exhibits the best agreement with the experimental data, especially in the prediction of the spectral position of the first absorption band (absorption threshold). Taking into account that such good agreement is found for a set of more complex organic systems like BAPQD this may be of substantial interest for chemical engineering which deals with the designing of new efficient organic luminophores for electroluminescent applications.

Spectral emission properties of 4-aryloxy-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]quinolines

Spectral emission properties of novel 4-aryloxy-1H-pyrazolo[3,4-b]quinolines were investigated. All of the compounds exhibit strong blue luminescence in the solution and in the solid state as well. Pyrazoloquinolines were used as dopants in PVK matrices in electroluminescent devices with ITO/PVK:PQ/Ca/Al light emitting diode configuration.

Photoluminescence of 1-phenyl,3-methyl pyrazoloquinoline derivatives

Paper presents the absorption and photoluminescence of 7-TFM, 6-F, 6-CN, 6-TBu and 6-COOEt derivatives of 1-phenyl-3-methyl-1H-Pyrazolo[3,4-b]quinoline (MPPQ). The measured spectra are compared with the results of the quantum chemical calculations performed by means of the semi-empirical methods (AM1 or PM3) that have been applied either to the equilibrium molecular conformations in vacuo (T=0K) or combined with the MD simulations (T=300 K). The photoluminescent spectra of MPPQ dyes are highly solvatochromic. The emission bands broaden and shift to the red with the increasing of solvent polarity, indicating thus a substantial dipole moment of the excited states. According to the quantum chemical analysis the reason for the strong solvatochromism of MPPQ dyes is related with intramolecular charge transfer (ICT) state. Due to the large dipole moment in the twisted geometry the ICT state is believed to become the lowest excited state in a strongly polar environment. This would explain a considerable solvatochromic shift in the highly polar solvents observed for all MPPQ dyes in the experiment. Such hypothesis is supported by the semi-empirical quantum chemical evaluations.

Molecular dynamics modeling in quantum chemical calculations. Optical absorption spectra of 1,3-Dimethyl-1H-Pyrazolo[3,4-b]quinoline derivatives

Paper presents the quantum chemical modeling of the optical absorption spectra of 6-fluoro, 6-bromo, 7-trifluoromethyl, 6-cyano and 6-carboethoxy derivatives of 1,3-Dimethyl-1H-Pyrazolo[3,4-b]quinoline. The calculations are performed by means of the semiempirical quantum chemical methods (AM1 or PM3) in combination with molecular dynamics (MD) simulations at T=300 K. It is shown that a particular rotational dynamics of the methyl, trifluoromethyl or ethyl groups practically does not influence the optical absorption in the spectral range 200-500 nm whereas broadening of absorption bands may be well reproduced within MD simulations including all types of nuclei vibrations. The results of calculations are compared with the measured spectra of optical absorption. The quantum chemical method AM1 in combination with MD simulations gives for all dyes the best agreement between the calculated and measured spectral positions of the first absorption band (absorption threshold).

Photovoltaic response and values of state dipole moments in single-layered pyrazoloquinoline/polymer composites

We report the photovoltaic response of composite films formed by polymer transport matrices poly(3-octylthiophene) (P3OT) and poly(3-decylthiophene) (PDT) with incorporated 1H-pyrazolo[3,4-b]quinoline (PAQ) chromophore (see the first figure). The photovoltage (PV) data were obtained for different substituted PAQ possessing different state dipole moments. The photovoltaic cells were formed between ITO and aluminum electrodes. We found that the PV signal of polymer/PAQ substantially depends on the state dipole moments of the pyrazoloquinoline chromophore. This fact indicates on a possibility of significant enhancement of PV efficiency by appropriate variations of the state dipole moments of chromophore. This results in photoinduced electron transfer from polymer serving as donors to PAQ being the electron acceptor. Despite an efficiency of the PV devices is below 1%, however, it may be substantially enhanced in future varying the chromophore state dipole moments appropriately.

Photoluminescence and electroluminescence of methoxy and carboethoxy derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline

A series of methoxy (MO) and carboethoxy (CE) derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline ([DPPQ]) are characterized by spectroscopic methods. All dyes show the photoluminescent spectra which are highly solvatochromic. In the case of 6MO[DPPQ] and 6CE[DPPQ] the emission bands are broad and shifted to the red with increasing of solvent polarity whereas the dyes 6MO1pMO[DPPQ] and 6MO13pMO[DPPQ] exhibit a reverse solvatochromism. The large difference between the excited- and state-dipole moments indicates a strong electron transfer effects in all dyes. The EL spectra are obtained for the fabricated OLEDs with a general structure of EL device ITO/PVK:6X[DPPQ]/Ca/Al. The blue emission originating from PVK host matrix appears to be quenched in EL spectra of doped PVK matrix giving rise to emission in blue, blue-green or green spectral regions. The obtained results demonstrate that a series of newly synthesized methoxy and carboethoxy [DPPQ]-derivatives may be considered as promising materials for electroluminescent applications.

Photoinduced transparency in polypyrrole films

For the first time we have discovered drastic photoinduced effects in the transparency for the pyrrole films. Photoinduced investigations of transparency were performed for the polypyrroles with different number of the pyrrole rings. We have established a considerable increase of the transparency from 70-75% up to 82-84% for the wavelengths of the probing lasers operating within the 530-1040 nm spectral range. The photoexcitation was performed by nanosecond pulsed polarized Nd-YAG laser generating at 1.34 microm. The phototransparent changes are completely reversible and disappear after switching off the laser treatment. The typical relaxation time for the photoinduced transparency is equal to about 10-20 micros and the changes of the transparency are strictly related with the values of state dipole moments of the polypyrroles. As a possible mechanism for explanation of the observed dependences one can consider existence of the charged trapping levels intra the forbidden energy gaps which effectively interact with the electric strength of the external polarized optical field and state dipole moments of the particular polymers.

Optical absorption of methoxy and carboethoxy derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline

Paper deals with experimental investigations and quantum chemical calculations of the optical absorption spectra of methoxy and carboethoxy 1,3-diphenyl derivatives of the pyrazoloquinoline ([PQ]): 6-methoxy-1,3-dyphenil-[PQ], 6-methoxy-1,3-(p-methoxyphenyl)-[PQ], 6-methoxy-1-(p-methoxyphenyl)-[PQ] and 6-carboethoxy-1,3-diphenyl-[PQ]. The quantum chemical calculations are performed by means of the semiempirical quantum chemical methods (AM1 or PM3) applied to: (a) the equilibrium molecular conformation in vacuo (T=0 K); (b) the molecular dynamic (MD) trajectory (T=300 K) which includes the dynamics of a certain molecular fragment (moiety) only (fragmental MD simulations); or (c) the MD trajectory obtained for most general case within the total MD simulations at T=300 K. The results of these calculations are compared with the measured spectra of the optical absorption. The quantum chemical simulations show that the dynamics of the methoxy or carboethoxy groups practically does not influence the absorption spectrum whereas the strongest its modification (300<lambda< or =360 nm) is found to be related with dynamics of phenyl(II) [Ph2] or phenyl(II)-methoxy [Ph2-MeO] moieties which are characterized by large libration amplitudes. At the same time, the total MD reproduces evidently much better the halfwidth of most absorption bands compared to ones observed in the measured spectra. Comparing the measured and calculated spectral positions of the absorption threshold the quantum chemical method PM3 gives the best agreement for all compounds.

Spectroscopy of PVK-phenyl derivatives disturbed the long-range ordering of liquid crystalline phase

It has been shown that replacing of O-CH3 substituents in PVK-phenyl derivative chromophores by C-N groups leads to appearance of long-ranged dipole-dipole interactions in the composites including PVK-CN, fullerenes and cyano-biphenyl derivatives. Following quantum chemical calculations it has been demonstrated that interaction of the chromophores with the LC matrices favors dipole-dipole ordering, however it description requires to take into account non-homogenous space charge density distribution. During doping by PVK-CN derivatives phase transition has been found from uniaxial system with pure nematic to the quasi-smectic LC state with the substantially different parameter of ordering. Moreover it was established that during this substitution the switching times drastically jump from millisecond to microsecond regime.

Influence of bond lengths between substituents and mother molecule on spectral properties of pyrazoloquinolines

Absorption and luminescent spectra of several new synthesized pyrazolo-quinoline possessing different substituents are studied. Absorption spectra of all the considered compounds possess five relatively strong absorption bands at about 430, 320, 270, 253 and about 230 nm. A correlation between the bond lengths between the substituent molecule and mother molecule with the observed spectral shifts was found. Theoretical spectra obtained within semi-empirical quantum chemical AM1 calculation methods seem to be more widened compared to the experimental ones due to electron-vibration interactions. However generally a good coincidence between spectral positions between experimental and calculated spectral peak positions was achieved. The corresponding experimental spectra have an absorption edges situated at about 430 nm which appears in fairly good agreement with quantum chemical simulations, namely for absorption spectra calculated by semi-empirical AM1-method. The red shifts in the experimental luminescence spectra are a consequence of electron-vibration interactions which increase with the effective radius and polarizabilities of the particular substituents.

Specific features of UV-vis absorption spectra of cis- and trans-polythiophenes

UV-vis optical spectra of several polythiophene with number of dimers n=1, 5, 10, 15 for cis- and trans-forms were investigated. The study was done theoretically using semi-empirical AM1 (Austin Model 1) and PM3 (Parametric Method 3) methods with the appropriate molecular geometry optimization. The experimental UV-vis absorption spectra were used for verification of the both semi-empirical theoretical models. With the increasing number of dimers a red shift of the absorption edge was observed. Solvent does not play a crucial role on behavior of the absorption spectrum. A comparison of the both semi-empirical methods with the observed experimental absorption spectra is performed. Role of state dipole moments of the investigated polythiophenes in the behavior of the observed UV-vis spectra is discussed. Particular role of pi-conjugated bonds is demonstrated.

Optical spectra of some 6-styrylo-1H-pyrazolo[3,4-b]quinolines

It was proposed a method of synthesis several 6-styrylo1-1H-pyrazolo[3,4-b]quinolines as promising material for optoelectronics. Particularly, 6-styryl-1,3-diphenyl-1H-pyrazolo[3,4-b]quinolines were prepared by Wadsworth-Emmons reaction. One of advantageous of these materials is stability of their optical spectra versus the possible cis- and trans-transformation. Theoretical and experimental studies of optical absorption and photoluminescence excitation spectra for styryloquinolines were done. They show that the AM1 semi-empirical method gives better results compared to other approaches. We have found that the solvents do not play a role in the behavior of the spectra. The backside-substituted groups do not influence substantially the observed optical spectra.

Optical poling effect and optical absorption of cyan, ethylcarboxyl and tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline: experiment and quantum-chemical simulations

We present here results of experimental studies and quantum-chemical simulations of optical absorption and optical poling effects performed on a new synthesized cyan, ethylcarboxyl and tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline incorporated into polymer matrix or dissolved in organic solutions. The efficiency of second-order optical susceptibility d vs photoinduced power density I(p) clearly saturates to certain magnitude d(eff) at sufficient power densities (I(p) > or = 1.3 GW cm(-2)). Comparing experimental data and results of semiempirical quantum-chemical simulations one can conclude that there exists generally a good correlation between the magnitude of saturated susceptibilities d(eff) and macroscopic hyperpolarizabilities for all compounds except the chromophore 1,3-dimethyl-6-cyano-[PQ] only. The discrepancy for this compound may reflect a specific contribution of surrounding polymer matrix. According to the quantum chemical analysis the methyl-containing cyan and ethylocarcoxyl derivatives reveal four/five strong absorption bands in the spectral range 200-500 nm. A substitution of the methyl groups by the phenyl group causes the substantial changes of the absorption spectra mainly in the spectral range 240-370 nm. Measured and calculated absorption spectra manifest rather good agreement mainly in the part regarding the spectral positions of the first oscillator (absorption threshold). The quantum-chemical PM3 method shows the best agreement with experiment. At the same time a considerable broadening almost of all absorption bands appears as a characteristic feature of all measured spectra. The discrepancies between the calculated and the measured spectra are attributed to electron-vibronic coupling as well as to a specific rotational dynamics of phenyl rings.

Optical absorption of 1H-pyrazolo[3,4-b]quinoline and its derivatives

The results of experimental studies and quantum chemical simulations of the absorption spectra of 1H-pyrazolo[3,4-b]quinoline and its derivatives are presented. The quantum chemical calculations (semi-empirical AM1 and PM3 methods) show similarity in the absorption spectra of 1H-pyrazolo[3,4-b]quinoline and 1,3-dimethyl-1H-pyrazolo[3,4-b]quinoline which are characterized by five strong absorption bands in the spectral range 200-500 nm. A substitution of the methyl groups by at least one phenyl group causes the drastic changes of the absorption spectra mainly within the spectral range 240-370 nm. We attribute these differences to additional molecular double bonding segments C=C of the substituted phenyl groups, i.e. to pi --> pi* transitions. A comparison of measured and the calculated absorption spectra manifests quite satisfactory agreement for all compounds in the part regarding the spectral position of the first oscillator (absorption threshold). At the same time, the measured spectra demonstrate the considerable broadening practically of all absorption bands and even complete damping some of them in the case of phenyl derivatives. The experiments performed with highly and weakly polar organic solvents shows that the solvent effect on the absorption spectra is small. For this reason the discrepancies between the calculated and the measured spectra are attributed to electron-vibronic coupling as well as to rotational dynamics of phenyl rings.