Energy transfer from probe

Otherwise, depolarization would also be a result of energy transfer between probe molecules. Because the transition moments of two interacting probes are unlikely to be parallel, this effect is indeed formally equivalent to a rotation. Moreover, artefacts may arise from scattering light that is not totally rejected in the detection system. 

Fluorescence energy transfer has been used to examine the distribution of bacteriorhodopsin in lipid vesicles using energy transfer from DPH to the acceptor retinal.(87) It was pointed out that care must be taken in fluorescence anisotropy studies if the fluorescence lifetime of a probe is decreased by energy transfer (in this case to retinal) since a shorter lifetime will lead to an erroneously high anisotropy value. 

Membranes fusion can be studied using the energy-transfer mechanism. In fact, membrane vesicles labeled with both NBD and rhodamine probes are fused with unlabeled vesicles. In the labeled vesicles, upon excitation of NBD at 470 nm, emission from rhodamine is observed at 585 nm as a result of energy transfer from NBD to rhodamine. The average distance separating the donor from the acceptor molecules increases with fusion of the vesicules, thereby decreasing the energy-transfer efficiency (Struck et al. 1981). 

The aggregation of the PMPS-PEO copolymers in solution and dispersion was fnrthered probed nsing flnorescence spectroscopy. A small red shift in the flnorescent emission maximnm was observed on increasing the water content, attributable to more effective energy transfer from shorter to longer PMPS segments. This indicated... 

Instrumental application of surface-plasmon-enhanced fluorescence was applied in using a TP scanning tunneling microscope [363], This was employed to probe the TP excited fluorescence from organic nanoparticles adsorbed on a silver surface. A size dependence of fluorescence enhancement and photodecomposition was reported as a result of competition between surface-plasmon-enhanced TP fluorescence and nonradiative energy transfer from the excited dye molecules to the silver surface. The schematic experimental setup is shown in Figure 3.14 [363]. 

At high excitation densities in the solid state, the decay of the singlet exciton becomes excitation dependant, bimolecular annihilation of the singlet exci-tons introduces a fast component to the decay [41,42,77,78], this is shown in Fig. 21. In a number of publications pump-probe spectroscopy has been used to study the phenomena surrounding this accelerated decay. The bimolecular annihilation reaction is effectively energy transfer from one excited singlet to... 

Note As for TRF, the term fluorescence is in fact misused in TR-FRET. In the spectroscopic Hteratirre, resonance energy transfer from a long-Hfetime probe such as a lanthanide chelate is termed LRET (luminescence RET) [121]. 

The first reported application of the technique by Kessler and Wilkinson [12] in 1981, deals with various aromatic hydrocarbons chemisorbed on Y-alumina. The samples were adsorbed at less than monolayer levels, and the transient spectra observed were shown to be due to triplet-triplet absorptions. Figure 6 shows the time resolved triplet-triplet absorption spectra obtained from 3% coverage of acridine on powdered silica [14] demonstrating the sensitivity of the method and its ability to probe acid-base reactions at catalytic surfaces. Turro and his coworkers [25,26] have studied various molecules on silica surfaces. The lifetimes of the triplet states of valerophenone and diphenyl-butyrophenone adsorbed on powdered silica were determined to be 0.3 and 0.9 [is, respectively [25] which is at least two orders of magnitude greater than in homogeneous solution. Turro et al [26] also demonstrated triplet energy transfer from benzophenone to naphthalene on silica surfaces via static and dynamic pathways. 

As mentioned already in the introduction energy transfer from ions having a strong absorption band to the rare-earth ions is a powerful tool by which the excited states of the latter can be populated. The absorption and emission maxima and the fluorescent quantum efficiencies of mercury-like ions and Ce3+ depend on the intrinsic properties of the host in which these ions are incorporated. In ref. (2) it was proposed that these ions may serve as a probe for the nephelauxetic effect, and Eu3+ for the electronegativity of glasses. 

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