Photo-excited fluorophore

Figure 3 (a) Orbital scheme illustrating the quenching of a photo-excited fluorophore (FI ) by a metal centre (M) the metal has now oxidizing tendencies and a Fl -to-M eT process t es place. In the ion pair that forms, FI", M , a back-eT process, from M to FI takes place fluorescence is quenched, (b) Thermodynamic cycle for the calculation of AG°ex. 

Figure 4 Orbital scheme illustrating the quenching of a photo-excited fluorophore FI by a nearby metal centre M via an electronic energy transfer (ET) mechanism. A simultaneous exchange of two electrons takes place, one from FI to M, one from M to FI. Following this circular electron motion, FI is deactivated. The excited M centre which is obtained can emit and relax to its ground state, but in most cases undergoes a non-radiative decay.

Fig. 10.5 The basis of an OFF/ON redox switch of fluorescence. Either an energy transfer (FT) or an electron transfer (cT) mechanism can be responsible for the quenching of the light emitting fragment fluorophore (FI ) in a multicomponent redox unit-spacer-fluorophore system. Switch efficiency requires that the control unit C in its oxidized form, quenches the proximate photo-excited fluorophore FI and the reduced form does not (OFF/ON switch). The other favorable on/off situation can be obtained when quenches FI and does not (Reprinted with permission from Bergonzi et al. 1998, Copyright 1998 Elsevier)...

The emissive counterpart to CD is circularly polarized photoluminescence (CPPL). Where the fluorophore is chiral, then the photo-excited state can return to the ground state with emission of circularly polarized light, the direction of polarization of which depends on the relative intensities of the right-handed and left-handed emissions (/r and /L, respectively), which in turn depends on the chirality of the material, or more accurately, the chirality of the photo-excited state of the material. CPPL studies on poly silanes are extremely rare, however, due to the low CPPL intensity and rapid sample degradation in solution, and problems due to artifacts in the solid state. 

Many phenomena other than fluorescence emission contribute to fluorophore deexcitation. These other alternatives to fluorescence are radiationless loss, phosphorescence, photo-oxidation, and energy transfer. Thus, the weaker the competitive phenomena, the higher the de-excitation via fluorescence. 

R5. The energy of a laser is higher than that of a lamp, thus allowing one to work at low fluorophore concentrations. However, since fluorophores are light-sensitive, excitation with a laser could accelerate the photo-bleaching rate. 

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