Forster energy transfer mediation

Furthermore the fluorescence lifetime of the donor molecules is significantly reduced as a consequence of efficient energy transfer to the lower energy trap. Since Forster energy transfer is mediated by dipole-dipole interaction without the need of direct overlap of orbitals, it can overcome distances up to 10 nm. It allows only singlet-singlet transition at low acceptor concentration and at a much faster rate of <10 s. 

Second, we present a Forster resonance energy transfer (FRET) imaging method, which has been used to monitor GPGR-mediated dissociation (activation) and reassociation (deactivation) of heterotrimeric G-protein in single live cells (10, 11). Protein/protein interactions cannot be measured by colocalization of the proteins because the limit of resolution of the light microscope using standard techniques is on the order of hundreds of nanometers, and one cannot be certain that two proteins of interest physically interact even... 

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. 

Forster and Dexter properly identified the microscopic interionic interaction leading to the communication between an excited and an unexcited ion as arising from the multipolar electrostatic fields produced by the excited state. In order to explain transfer in lanthanide doped systems where often there is no direct overlap in the sharp line spectra of acceptor and donor ions, it becomes necessary to invoke phonon assistance to conserve energy which entail the emission and absorption of one or more phonons. As in the case of relaxation, the various phonon mediated transfer processes have characteristic temperature dependences which allow their identification. The microscopic processes have also definite parametric dependences such as on Rj, the distance between interacting centers, on the amount of energy to be taken up or supplemented by... 

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