Energy transfer Forster type

In addition,<1,48,48) it was noted that whereas the azulene effect on the sensitized reaction is sensitive to changes in solvent viscosity, the azulene effect on the direct photoreaction was independent of solvent viscosity, as would be predicted for Forster-type energy transfer. The inescapable conclusion is that cis-trans isomerization upon direct irradiation of stilbene takes place in the singlet manifold. 

It is possible to estimate the rate of vertical singlet energy transfer (9.31) and (9.33) (when Forster-type energy transfer is negligible, spectral overlap integral is very small) from the relation... 

Roda A, Guardigli M, Michelini E et al (2009) Nanobioanalytical luminescence Forster-type energy transfer methods. Anal Bioanal Chem 393 109-123... 

SAOTS was established to be a true monolayer (rather than a bi- or multilayer) by conductivity and Forster-type energy transfer measurements [183]. Energy transfer experiments were carried out on a composite system which consisted of a mixed OTS and donor cyanine dye (D) monolayer on a glass slide, on top of which a mixed cadmium arachidate acceptor cyanine dye (A) monolayer was deposited (by the LB technique) in such a manner that it covered only half of the glass slide. The other half was covered by a pure... 

The presence of an orientation factor in the equation for Forster-type energy transfer has led to the study (63-67) of nonconjugated bichromophores held together by a rigid link, in such a way as to fix the orientation of one chrompphore with regard to the other one, for example, [18] (63). 

The fluorescence studies of the interaction of cytochrome c with the anilinonaphthalene sulfonate-apoenzyme and protoporphyrin-apoenzyme complexes provide another line of evidence (39) in support of the above-mentioned conclusion. Both fluorescence steady-state and lifetime titrations of these fluorescence-labeled apoenzymes with ferro- and ferricytochrome c indicates the formation of a 1 1 complex, the affinity for ferricytochrome c being less than that for ferrocytochrome c. From the phosphorescence and fluorescence quenching, the distance between the emitter (a fluorescence label) and the quencher (the heme of cytochrome c) can be calculated by assuming that no direct electronic interaction exists between them, and that the quenching is derived from the Forster-type energy transfer (65) to the heme. The distance from the apoenzyme-bound emitter to the heme group of cytochrome c is estimated to be 19 A and 14 A for the anilinonaphthalene sulfonate and protoporphyrin... 

The energy transfer in this matrix occurs in different ways. They are (i) Forster type energy transfer, (ii) Dexter transfer (iii) Exciplex - excimer charge transfer and (iv)Trap assisted... 

Forster-type energy transfer from aequorin to GFP suggested ... 

Crystallization of GFP, and the first demonstration of the in vitro Forster-type energy transfer from aequorin to GFP ... 

Minkowski, C., Calzaferri, G., Forster type Energy Transfer along a Specified Axis, Angew. Chem. Int. Ed. 2005, 44, 5325 5329. 

The other alternative for exciton quenching due to doping is Forster-type energy transfer towards a chromophore with bathochromatically shifted absorption spectrum so that the spectral overlap between the donor and acceptor absorption is larger. An example is fluorescence quenching in a film of poly(phenyl-pheny-lene-vinylene) (PPPV) blended with polycarbonate (PC) at a PPPV PC ratio of 20 80 per weight and doped by the 4-dicyanomethylenc-2-methyl-6-p-dimcthyla-... 

Fig. 11.6 Scheme illustrating various transfer processes from the host to the guest electron (hole) transfer from the host LUMO (HOMO) to the guest LUMO (HOMO), Forster-type energy transfer between singlet states and Dexter-type energy transfer from the host to the guest triplet state. The nature of the excitonic state is simplified for better clarity. 

Fig. 3 shows fluorescence intensity of FCLA in the presence of HSA (/lex=288 nm). Intensity increased greatly in the presence as compared to the absence of HSA in the same conditions as for the studies shown in Fig. 3. This provides strong evidence for the occurrence of Forster type energy transfer from the tryptophan moiety (donor) in HSA to the FCLA molecule (acceptor). We know that the distance from bonded-FCLA to Trp214 is less than 5 nm. Therefore, efficient energy transfer can exist between HSA (donor) and FCLA (acceptor).

Secondly, energy deposited within the bulk by excitation of a correlated electron—hole pair (exciton) may transfer by Forster-type energy transfer to, and become localised on, a pair of adjacent surface states as represented by... 

Further evidence of Forster-type energy-transfer effects has been obtained for several excited triplet-state donors and several ground-state doublet nitroxyl radicals. Critical transfer distances of the order of 12—20 A were measured and were on good agreement with calculated values. 

We have previously shown that when PPV is self-assembled with specific electronically active polyanions such as poly(thiophene acetic acid) (PTAA) or sulfonated fiillerenes (S-C60 )(7), the photoluminescence of the PPV is essentially completely quenched by the polyanion. The mechanism of this quenching is believed to be due to a photoinduc electron transfer process taking place between the excited PPV and the adjacent electroactive polyanion molecules. The quenching process, in this case, is not associated with a Forster type energy transfer since in both cases, the required spectral overlap of a donor emission band with an acceptor absorption band is not fulfilled. In addition, photo-induced electron transfer processes have previously been confirmed in PPV/C60 systems and can be exploited to fabricate thin film photovoltaic devices (77). In order to mediate this electron transfer process, we have constructed multilayer heterostructures in which the PPV donor and the polyanion electron acceptor are separated from each other with electronically inert spacer layers of known thickness. In addition to allowing studies of the electron transfer process, such structures provide important insights into the thermal stability of the multilayer structure. The "spacers" used in this study were bilayers of SPS/PAH with an experimentally determined bilayer thickness of 30 +/-5 A. 

However, in contrast to surface enhanced Raman scattering (SERS), maximal enhancement of fluorescence is not observed from molecules that are directly adsorbed on the surface, but from those that are located at a short distance away from the metal surface. The reasons are two counterbalancing effects and can be deduced from Fig. 17a [117]. First, if positioned too close to the metal surface, Forster-type energy transfer can set in and Z((Weni) is rapidly reduced because of the onset of non-radiative quenching (Fig. 17a, dotted line for the influence on the radiative rate constant, see Sect. 2.1) [118]. Second, if the dye is placed too far from the metal surface, coupling is inefficient because the induced field is an evanescent field and its intensity decays exponentially with the distance from the surface (Fig. 17a, solid line). For instance, considering a gold surface and water as the dielectric, the field has decayed to 1/e at ca. 150 nm. Thus, a maximum enhancement Z(mem) exists only in a small zone at an optimum distance from the metal surface. For the Au/water system in... 

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