Tomasz Uchacz

UV–vis spectroscopy and semiempirical quantum chemical studies on methyl derivatives of annulated analogues of azafluoranthene and azulene dyes

Paper reports the measured optical absorption and fluorescence spectra of 4-(2-chlorophenyl)-7-methyl-1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline (MCPDPPQ), as well as 6-methyl-1,3-diphenyl-3H-indeno[1,2,3-de]pyrazolo[3,4-b]quinoline (MDPIPQ) and 9-methyl-6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene (MPTNA) representing cyclized five- or seven-membered regioisomeric products of MCPDPPQ, respectively. The spectra has been recorded in solvents of different polarity and compared with the results of quantum chemical calculations performed by means of the semiempirical method PM3 in combination with molecular dynamics (MD) simulations. Cyclization of MCPDPPQ into MDPIPQ or MPTNA is accompanied by a significant red shift of the first optical absorption and fluorescence bands. While the solvent polarity rises all the dyes exhibit the blue shift of the first absorption band and the red shift of the fluorescence band. These trends have been reproduced within the semiempirical calculations in combination with the Lippert-Mataga dielectric polarization model and explained by specific orientations of the dipole moments in the ground and excited states. All dyes may be considered as candidates for the luminescent or electroluminescent applications. Depending on solvent polarity they emit light in the green-yellow range of the visible spectra.

DFT/TDDFT Study on the Electronic Structure and Spectral Properties of Diphenyl Azafluoranthene Derivative

Paper reports the DFT/TDDFT study on the electronic structure and spectral properties of the five-membered annulated diphenyl azafluoranthene derivative 1,3-diphenyl-3H-indeno[1,2,3-de]pyrazolo[3,4-b]quinoline (DPIPQ) by means of polarizable continuum model (PCM) and Onsager reaction field approaches at the B3LYP/6-31+G(d,p) level of theory. The results of calculations are compared with the optical absorption and fluorescence spectra as well as with the cyclic voltammetry data. The DFT/TDDFT/PCM approaches exhibit rather good quantitative agreement regarding the spectral position of the first absorption band; the discrepancy between the experiment and theory is less than 0.06 eV (linear response approach) or 0.25 eV (state specific approach). As for the fluorescence emission the TDDFT/PCM calculations underestimate the transition energy on about of 0.7–0.8 eV. Such discrepancy should be attributed to insufficient quality of the TDDFT/PCM optimization in the excited state. Ignoring the geometrical relaxation in the excited state provides considerably better agreement between the experiment and theory; discrepancy is less than 0.1–0.22 eV depending on a solvent polarity. The dominant influence on the fluorescence emission results mainly from the solvent reorganization in the excited state whereas the solute relaxation is indeed weak and may be ignored.

A pilot study of the novel J-PET plastic scintillator with 2-(4-styrylphenyl)benzoxazole as a wavelength shifter

For the rst time a molecule of 2-(4-styrylphenyl)benzoxazole containing benzoxazole and stilbene groups is applied as a scintillator dopant acting as a wavelength shifter. In this article a light yield of the plastic scintillator, prepared from styrene doped with 2 wt% of 2,5-diphenylbenzoxazole and 0.03 wt% of 2-(4-styrylphenyl)benzoxazole, is determined to be as large as 60% 2% of the anthracene light output. There is a potential to improve this value in the future by the optimization of the additives concentrations.

Synthesis and Spectroscopic Study of Several Novel Annulated Azulene and Azafluoranthene Based Derivatives

A series of cyclized five-membered annulated azafluoranthene (AAF) and seven-membered annulated azulene (AA) derivatives have been synthesized and characterized by spectroscopic methods. The optical absorption and fluorescence spectra have been recorded in organic solvents of different polarity and analyzed within the semiempirical quantum chemical model PM3. In combination with the molecular dynamics simulations it properly reproduces the overall shape of the measured absorption spectra of both AA and AAF dyes including the strongest band in the region of 250–300 nm and the broad first absorption band above 400 nm. While the solvent polarity rises all the dyes exhibit the hypsochromic shift of the first absorption band and the bathochromic shift of the fluorescence band. Such opposite solvatochromic trends appear to be consistent with the Lippert–Mataga solvatochromic model. Compared to AA compounds, both AAF dyes reveal much stronger solvatochromic shift and broadening of the fluorescence band likewise the relative decrease in quantum yield on rising solvent polarity what may be an evidence for the intramolecular charge transfer mechanism being involved into the fluorescence emission. Depending on solvent polarity AA and AAF dyes emit light in the green–yellow range of the visible spectra what may be of interest for potential luminescent or electroluminescent applications.

New Fluorescent Sensors Based on 1H-pyrazolo(3,4-b) quinoline Skeleton

Novel fluorescing dyes 1,3,4-triphenyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl)-1H-pyrazolo[3,4-b]quinoline (K1) and 2-[(2-hydroxyethyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amino]ethanol (L1) have been synthesized and investigated by the means of steady state and time-resolved fluorescence techniques. These compounds act as sensors for the fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium and calcium) in solvents of different polarities (THF and acetonitrile). The mechanism, which allows application of these compounds as sensors, is an electron transfer from the electro-donative part of molecule to the acceptor part (fluorophore), which is retarded upon complexation of the electro-donative part by inorganic cations. We found that crown ether-containing compound is very sensitive to the addition of any investigated ions but amino alcohol-containing one exhibits better selectivity to the addition of two-valued cations. Two kinds of the complexes (LM+ and L2M+) were found in the investigated systems. In addition, the dyes may be used as fluorescence indicators in solvents of lower polarity like tetrahydrofuran.

A New Fluorescent Sensor Based on 1H-pyrazolo[3,4-b]quinoline Skeleton. Part 2

A novel fluorescent dye bis-(pyridin-2-yl-methyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amine (P1) has been synthesized and investigated by means of steady state and time-resolved fluorescence techniques. This compound acts as sensor for fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium, calcium, and zinc) in highly polar solvents such as acetonitrile. The mechanism which allows application of this compound as sensor is an electron transfer from the electron-donative part of molecule (amine) to the acceptor part (pyrazoloquinoline derivative), which is retarded upon complexation of the electro-donative part by inorganic cations. The binding constants are strongly dependent on the charge density of the analyzed cations. The 2/1 complexes of P1 with Zn++ and Mg++ cations posses large binding constants. Moreover, in the presence of these cations a significant bathochromic shift of fluorescence is observed. The most probable explanation of such behaviour is the formation of intramolecular excimer. This is partially supported by the quantum chemical calculations.

Solution processable double layer organic light emitting diodes (OLEDs) based on 6-N,N-arylsubstituted-1H-pyrazolo[3,4-b]quinolines

Abstract Three 1H-pyrazolo[3,4-b]quinolines (PQs) with N,N-diarylamine moiety were synthesized. They were used as dopants in poly(9-N-vinylcarbazole) (PVK) matrice. An additional star burst oligoquinoline TRI-Q electron transporting layer was deposited on emission layer from solution. The devices with configuration ITO/PEDOT:PSS/PVK-PQ/TRI-Q/Ca/Al show bright green emission with luminance L = 355–806 cd m−2.

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

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.

Applications of Fluorescent Sensor Based on 1H-pyrazolo[3,4-b]quinoline in Analytical Chemistry

Fluorescent dye 2-[(2-Hydroxyethyl)-(1,3-diphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amino]ethanol (LL1) was examined for its efficiency in the detection of small inorganic cations (lithium, sodium, barium, calcium, magnesium, cadmium, lead and zinc). The dye was synthesized in the laboratory and investigated by means of both, steady-state and time-resolved fluorescence techniques. This compound acts as a fluorescent sensor suitable for detection of small inorganic cations (lithium, sodium, barium, calcium, magnesium, cadmium, lead and zinc) in strongly polar solvent (acetonitrile). An electron transfer from the electro-donative part (receptor) of the molecule to the acceptor part (fluorophore) is thought to be the main mechanism that underlies functionality of the compound as a sensor. This process can be retarded upon complexation of the receptor moiety by inorganic cations. Relatively high sensitivity but poor selectivity of the aminoalcohol thatcontains indicator towards the two-valued cations was observed. However, upon addition of some amounts of water the selectivity of this sensor has been enhanced (especially towards lead cation). The preliminary results in analytical application of the sensor are discussed.

On the spectral properties of methyl and methoxy derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoxalines: Experiment and DFT/TDDFT calculations

Paper reports the synthesis and spectroscopic studies of two novel 1,3-diphenyl pyrazoloquinoxaline (PQX) derivatives with 6-substituted methyl (MePQX) or methoxy (MeOPQX) side groups. The optical absorption and fluorescence emission spectra are recorded in solvents of different polarity. Other photophysical constants, such as the fluorescence lifetime and quantum yield, radiationless and radiative rate constants, electronic transition dipole moments, give complete characterization of MePQX and MeOPQX dyes as materials for potential luminescence or electroluminescence applications. Measured optical absorption and fluorescence emission spectra are compared with the results of quantum-chemical analysis using density functional theory (DFT/TDDFT) methods based on hybrid and long range corrected (LRC) exchange-correlation (xc) functionals in combination with solvation self consistent reaction field model. Comparing to conventional hybrid xc-functionals, the DFT/TDDFT calculations using LRC xc-functionals yield considerably more accurate description of optical absorption and fluorescence emission spectra. The best description of the absorption-emission circle provides the model assuming that optical absorption takes place from preferably flat or weakly twisted molecular conformations in the ground state, as particularly is suggested by the geometrical DFT optimization, whereas the fluorescence emission would be expected from more twisted molecular conformations in the excited state.