Miklós Kubinyi

Vibrational spectra and normal coordinate analysis of phenol and hydroquinone

Abstract The infrared and Raman spectra of hydroquinone have been recorded in solution and in crystalline state (β-modification). The spectra have been assigned with the help of normal coordinate analysis. The calculations have been performed for phenol and the two planar conformers of hydroquinone. The force constants have been computed with the CNDO force method. The scaling factors obtained by fitting the calculated frequencies of phenol to the observed ones have been transferred to hydroquinone.

Determination of the thickness and optical constants of thin films from transmission spectra

Abstract A method has been developed to determine the thickness and the wavelength-dependent refractive indices and absorption coefficients of thin optical films by fitting a five parameter function to measured transmission spectra. Initial values for the fitting parameters are obtained from the transmission values at the spectral maxima and minima of the interference patterns created by the films. This is followed by a systematic variation of those parameters which can cause a failure of the calculation by reaching local minima of the residual sum of squares. The final fitting is performed with a Marquardt algorithm. A Monte Carlo simulation has indicated that the accuracy of this method is at least one order of magnitude better than that of the methods utilising only the interference extrema.

Quantum chemical studies on excited state intermolecular proton transfer of oxazine dyes

Abstract The excited state lifetimes of oxazine dyes nile blue and oxazine 720 show a significant solvent dependence. As an aid to the interpretation of the decay in acidic environments the ground electronic states and the first singlet excited states of oxazine monocations and dications have been studied by methods of quantum chemistry. Ab initio calculations carried out on the lower members on this series show a significant increase of the electron densities of the ring nitrogen on excitation. The calculated electron energies also suggest that the second proton attaches to the ring nitrogen in the excited states, in contrast to the ground states where (in the case of oxazine 720) the second proton attaches to the terminal nitrogen. A kinetic scheme is proposed for the decay process in which in acidic environments the main deactivation path is the reaction of excited state monocations with protons, followed by internal conversion and subsequent deprotonation of the ground state dications.

Synthesis of chiral 1,3-calix[4](crown-6) ethers as potential mediators for asymmetric recognition processes

Abstract Novel chromogenic 1,3-calix[4](crown-6) derivatives comprised of 1,1′-binaphthyl-, methyl-α- d -glucoside-and d -mannitol moieties in the crown ether ring have been synthesized. UV–vis spectroscopic measurements of the 2,4-dinitrophenylazo chromogenic molecules indicated noticeable chiral discrimination associated with coloration towards primary amine enantiomers.

Rotational reorientation dynamics of nile blue A and oxazine 720 in protic solvents

Abstract The temperature dependence of the orientational relaxation times of the cationic oxazine dyes nile blue A and oxazine 720 have been determined in water, methanol, ethanol and ethyleneglycol, by measuring the picosecond decays of the polarization dichroism of transient absorption signals. It has been shown that the observed orientational relaxation times are attributed to the ground state solutes. The equilibrium geometries of the two ground state cations, their dipole moments and their atomic charge distributions have been computed in accurate density functional calculations. The hydrodynamic and dielectric contributions to the orientational relaxation times have been estimated on the bases of generalized Stokes–Einstein–Debye theory and of point charge dipole approach, using the molecular parameters obtained in the quantum chemical calculations. The results indicate that the solvent shells around the solutes significantly enhance the orientational relaxation times. The temperature dependence of this effect is negligible in water and methanol, small, but observable in ethanol, and strong in ethyleneglycol.

Triplet state spectroscopic studies on some 5,10,15,20-tetrakis(methoxyphenyl)porphyrins

Abstract Extensive triplet state spectroscopic investigations were carried out with a series of 5,10,15,20-tetrakis(methoxyphenyl)porphyrins. Triplet absorption spectra, triplet lifetime, triplet quantum yield and quantum yield for singlet oxygen production were determined with different absorption and emission techniques, using the frequency-doubled beam of a Nd:YAG laser. It has been found that these synthetic porphyrins are effective photosensitizers which can be used as model compounds to investigate the theoretical and instrumental aspects of PDT.

Intermolecular photoinduced proton transfer in nile blue and oxazine 720

Abstract The S1 excited state lifetimes of laser dyes nile blue (NB) and oxazine 720 (OX) have been determined in acidic aqueous solutions as functions of pH. The decay constant show a linear dependence on [H+], with an identical slope for both molecules. The reason for the faster decay in acidic solutions results from the formation of dications by reaction of excited state monocations with hydrogen ions. These results suggest that in the excited state reaction the additional proton locates on the ring nitrogen atom rather than on the terminal amino groups.

Photochromism of a spiropyran derivative of 1,3-calix[4]crown-5

A new spiropyran derivative containing a calixcrown ring has been synthesised. Thermal conversion from merocyanine to the spiropyran form was studied in ethanol and in acetonitrile, and equilibrium and kinetic data were compared with those of the parent 6-nitrospiropyran. The kinetics of thermal decay of the merocyanine form of the calixcrown-spiropyran molecule shows a biexponential character in both solvents, while the decay is much slower in ethanol than in acetonitrile.

Optical spectroscopic studies on the complexation of stilbazolium dyes with a water soluble pillar[5]arene

The host–guest interactions of a water soluble carboxylato-pillar[5]arene (WPA5) and three stilbazolium dyes (containing 9-anthryl, 1-pyrenyl and 4-dimethylaminophenyl groups) were studied by UV-Vis and fluorescence spectroscopy giving a detailed description of the spectral changes. A different spectroscopic response was observed in each case, with the most significant result of 28-fold fluorescence enhancement and intense color change in the case of 4-dimethylaminostyryl-N-methylpyridinium iodide (DAST, G3). In addition, a FID (fluorescence indicator displacement) system comprised of WPA5 and G3 was shown to detect paraquat by turn-off fluorescence in aqueous solution.

Fluorescence decay dynamics of organic dye molecules in solution

Abstract A picosecond laser system consisting of two tuneable dye lasers pumped synchronously by a mode locked argon-ion laser has been used for studying the relaxation of the S 1 excited states of dye molecules Nile Blue and Oxazine 720. The dependence of the excited state lifetimes on the solvent and on the temperature are discussed. Both intramolecular and intermolecular decay channels contribute to the radiationaless de-excitation. The mechanism of intramolecular decay is different, while that of intermolecular decay is very similar for the two molecules.