A. Kawski

FLUORESCENT DIMERS OF RHODAMINE 6G IN CONCENTRATED ETHYLENE GLYCOL SOLUTION

Abstract Aggregation of rhodamine 6G in concentrated ethylene glycol solutions is studied as a function of temperature. The measurements of absorption and fluorescence spectra evidence that the system of interest consists of two fluorescent species: monomers and dimers. Strong overlaps between all absorption and fluorescence bands in this system enable forward and reverse energy transport between monomers and dimers. The quantitative analysis of the effect of nonradiative energy transport (NET) on the fluorescence spectra as well as on the fluorescence quantum yields of monomers and dimers explains the temperature and concentration regularities observed. In particular, it is shown that in the concentrated solution the calculated monomer quantum yield is underrated compared to that measured, if the reverse NET is neglected. The lack of information on the value of the dimer quantum yield does not allow for full analysis of the forward and reverse NET in the system. However, it is shown that if that quantum yield is determined as the best fit parameter, an excellent agreement between the experimental and calculated values is obtained.

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.

Nonradiative excitation energy transport in one-component disordered systems.

AbstractHigh-accuracy Monte Carlo simulations of the time-dependent excitation probabilityGs(t) and steady-state emission anisotropyrM/r0M for one-component three-dimensional systems were performed. It was found that the values ofrM/r0M obtained for the averaged orientation factor

The Influence of Reverse Energy Transport on Emission Anisotropy in Two-Component Viscous Solutions

\overline {\kappa ^2 }

Thermochromic Absorption, Fluorescence Band Shifts and Dipole Moments of BADAN and ACRYLODAN

only slightly overrate those obtained for the real values of the orientation factor κik2. This result is essentially different from that previously reported. Simulation results were compared with the probability coursesGs(t) andR(t) obtained within the frameworks of diagrammatic and two-particle Huber models, respectively. The results turned out to be in good agreement withR(t) but deviated visibly fromGs(t) at long times and/or high concentrations. Emission anisotropy measurements on glycerolic solutions of Na-fluorescein and rhodamine 6G were carried out at different excitation wavelengths. Very good agreement between the experimental data and the theory was found, with λex≈λ0-0 for concentrations not exceeding 3.5·10−2 and 7.5·10−3M in the case of Na-fluorescein and rhodamine 6G, respectively. Up to these concentrations, the solutions investigated can be treated as one-component systems. The discrepancies observed at higher concentrations are caused by the presence of dimers. It was found that forλex λ0-0), they lie higher than the respective theoretical values. Such a dispersive character of the energy migration can be explained qualitatively by the presence of fluorescent centers with 0-0 transitions differing from the “mean” at λ0-0.

Tautomerism and stereoisomerism of nitracrine, its nitro isomers and their protonated forms in solution examined by absorption and fluorescence spectroscopy

The fluorescence of ACRYLODAN (6-acryloyl-2-dimethylamino-naphtalene) consists of two bands in liquid polar solvents like 1,2-dichloroethane, N,N-dimethylformamide, or acetonitrile. The intensity ratio of long emission (LE) and short emission (SE) bands, LE/SE, depends on the excitation wavelength. For λexc = 420 nm only LE band appears. The observed two fluorescence bands of ACRYLODAN in polar solvents containing trace amounts of water originate from two different components: LE of ACRYLODAN and SE of the product resulting from hydrolysis back to 2-dimethylaminonaphtalenic acid.

Ground and Excited State Dipole Moments of LAURDAN Determined from Solvatochromic and Thermochromic Shifts of Absorption and Fluorescence Spectra

The effect of nonradiative reverse energy transport (NRET) in two donor-acceptor systems was studied experimentally. It was found that the NRET occurring in system I; rhodamine 6G (donor) and rhodamine B (acceptor), considerably lowers the emission anisotropy at medium and high concentrations. These results qualitatively confirm the predictions of the approximate theoretical approach of L. Kulak and C. Bojarski (see the preceding paper). In system II; rhodamine 6G (donor) and Nile Blue (acceptor), for which the NRET process does not occur, a good agreement with no-back-transport theory was obtained.

Einfluß der Polarität und Viskosität des Lösungsmittels auf die Deaktivierung des S1-Zustandes von Donator-Akzeptor-substituiertentrans-Stilbenen

Abstract The effect of concentration depolarization of donor (D) fluorescence in the presence of an acceptor (A) for two D-A systems differing in critical radii ratio, R 0DA R 0DD , and with constant reduced concentration ratio ( γ D γ A ) was investigated. According to the theory of Loring, Andersen and Fayer, the emission anisotropy measurements confirmed different concentration dependences for both systems at high concentrations. The effect of R 0DA / R 0DD upon the emission anisotropy changes in the subsystems with weak and strong energy migration, as well as the influence of the correlation effect on the concentration depolarization of fluorescence is discussed. Modern theories of nonradiative excitation energy transport in two-component systems were compared in the light of the experimental data obtained.