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A β-cyclodextrin labeled with seven naphthoyloxy chromophores was studied by steady-state and time-resolved fluorescence spectroscopy in order to get information on the dynamics of energy hopping between chromophores. The steady-state fluorescence anisotropy was recorded as a function of excitation wavelength in a mixture of methanol and ethanol at 110 K (rigid glass). The fluorescence anisotropy decay was obtained under the same conditions by the multifrequency phase-modulation technique upon excitation at 290 nm. The data were analyzed and interpreted on the basis of a theoretical model involving a unique rate constant for energy hopping between nearest neighbors. In particular, this model predicts a long-time leveling-off of the emission anisotropy at 1/7th of the fundamental anisotropy, which is confirmed by both steady-state and time-resolved data and thus indicates that there is no preferred mutual orientation between the chromophores. As regards the rate of energy hopping, an average value of 2 × 109 s-1 can be deduced from the comparison between the theoretical and experimental decays. This value is shown to be consistent with a dipole-dipole mechanism of energy transfer. © 1996 American Chemical Society.

Dynamics of intramolecular electronic energy transfer in bichromophoric molecules, consisting of two coumarins linked by a variable number of methylene groups, is investigated by multifrequency phase-modulation fluorometry. From observation of the acceptor delayed emission, information on the rate of transfer can be obtained. © 1985.

Fluorescence depolarization by energy transfer resulting from dipole–dipole interaction (Förster type) is studied in donor–acceptor pairs of like and unlike chromophores at a fixed distance and with random and uncorrelated static orientations. For unlike chromophores, the acceptor anisotropy decay is shown to display three different extreme types of behavior. When the intrinsic decay rate of the acceptor is much faster than both the transfer rate and the donor intrinsic decay rate, the acceptor anisotropy decays from a positive value, then rises and passes through a maximum, and finally tends to a negative limiting value, yielding a zero steady-state value. The existence of a maximum is shown to be due to the peculiar relation between the orientation factor and the average angle formed by the donor and acceptor transition moments. For pairs of like chromophores, the exact anisotropy is calculated and compared with that given by an approximate treatment. It is also shown that the anisotropy of the indirectly excited partner varies with time, tending to zero, in contradiction to previous work, where it is reported to be 4% of that of the directly excited chromophore. [ABSTRACT FROM AUTHOR]

The fluorescent dye 1-anilinonapthalene-8-sulfonic acid (ANS) has been used as a probe of changes in membrane conformation accompanying excitation of the electroplax ofElectrophorus electricus. ANS binds reversibly to the excitable membrane at rest. During generation of an action potential, an increase in ANS-fluorescence intensity is observed which resembles but does not strictly follow the membrane potential. Experiments using the current-clamp technique have demonstrated a linear relationship between the change in membrane potential and the change in ANS fluorescence intensity. The change in fluorescence intensity is not a consequence of binding to membrane sites of increased affinity nor of an electrophoretic concentration of ANS molecules at the membrane surface.It is not known whether the change in fluorescence intensity is due to a change in quantum yield of bound ANS or to an increase in the amount of bound ANS. In either case, the change in fluorescence intensity may be interpreted as a change in membrane conformation. [ABSTRACT FROM AUTHOR]