Aleksander A. Kubicki

Unusual absorption and fluorescence properties of 1,6-diphenyl- 1,3,5-hexatriene in poly(vinyl alcohol) film

Abstract The effect of temperature on the absorption and fluorescence properties of 1,6-diphenyl-1,3,5-hexatriene (DPH) in poly(vinyl alcohol) (PVA) film was investigated in the range 295–428 K. On heating above 353 K, the optical density (in the long-wavelength region) and the quantum yield of DPH increase rapidly. This effect is irreversible, i.e. once the sample is heated it retains its absorbance and fluorescence quantum yield on cooling to room temperature. It has its origin in the cis—trans conversion of DPH molecules in the PVA melt at high temperatures.

Anomalous behaviour of emission anisotropy for short living derivatives of stilbene

Abstract Stilbene and its derivatives are often used as fluorescent probes to study photophysical properties of different media. These compounds are characterized by a high quantum yield and a very short mean excited state lifetimes what allows studying changes of emission anisotropy r as a function of both excitation and observation wavelength. In this Letter absorption, fluorescence as well as polarization excitation and emission spectra are presented for stilbenes in solvents of different viscosity and polarity. Higher emission anisotropy values in the absorption band are observed which stay at the same level upon excitations different than those corresponding to the 0–0 transition wavelength. It can be explained by the presence of two luminescent centers contributing to emitted light or by incomplete relaxation of the excited states before emission.

Transition moment directions and selected spectroscopic properties of Ivabradine

Based on the Kawski-Gryczynski method the value of angle β=38° between absorption and fluorescence transition moments of Ivabradine was determined. Such a high value of β is responsible for low emission anisotropy of Ivabradine in a rigid polyvinyl alcohol matrix and in anhydrous glycerol despite the elongated shape of the fluorophore. Selected steady-state and time-resolved spectroscopic results support the analysis.

Electronic Excitation Energy Migration in Partly Ordered Polymeric Films

Multistep intermolecular energy migration between elongated fluorophores (carbocyanines) in uniaxially oriented polymer films is studied based on fluorescence depolarization and Monte-Carlo simulations. Contrary to disordered systems it is found experimentally that the concentration depolarization of fluorescence in uniaxially oriented films is extremely weak despite effective energy migration. Based on the concentration depolarization experiment in the ordered matrix it is possible to estimate the angle between absorption and fluorescence transition moments of carbocyanines. The values of that angle are very close to those obtained from other methods.

Förster Resonance Energy Transfer and Trapping in Selected Systems: Analysis by Monte-Carlo Simulation

Monte-Carlo simulation method is described and applied as an efficient tool to analyze experimental data in the presence of energy transfer in selected systems, where the use of analytical approaches is limited or even impossible. Several numerical and physical problems accompanying Monte-Carlo simulation are addressed. It is shown that the Monte-Carlo simulation enables to obtain orientation factor in partly ordered systems and other important energy transfer parameters unavailable directly from experiments. It is shown how Monte-Carlo simulation can predict some important features of energy transport like its directional character in ordered media.