Forster’s mechanism

The spectroscopic characteristics of actinide and lanthanide luminescent probes are sensitive to numerous parameters, such as modifications of solvent composition, addition of supporting electrolytes, temperature changes etc. Therefore, TRES appears as an interesting tool for the chemist, because it provides sensitive experimental data. However, the interactions between the probe and the surrounding medium (in a wide sense) appear to be intricate and difficult to handle. In this sense, attempts to describe lifetime variations as a function of a unique parameter, the hydration sphere number, have shown their limitations. On the other hand, the open questions related to Forster s mechanism are a vivid and still not fully explored field. 

FRET intensity can be expressed in function of the distance of the two molecules as shown in eq. (1) assuming a dipole-dipole (Forster s) mechanism for the energy transfer. This gives the basis for calculating the distance of two molecules by measuring FRET intensity ... 

Energy transfer can result from different interaction mechanisms. The interactions may be Coulombic and/or due to intermolecular orbital overlap. The Coulombic interactions consist of long-range dipole-dipole interactions (Forster s... 

Forster s formulation of long-range dipole-dipole transfer (very weak coupling) Forster derived the following expression for the transfer rate constant from classical considerations as well as on quantum-mechanical grounds ... 

HUl, C.A.S., Forster, S., Farahani, M.R.M., Hale, M.D.C. and Williams, G. (2005). An investigation of cell wall micropore blocking as a possible mechanism for the decay resistance of anhydride modified wood. International Bio deterioration and Biodegradation, 55(1), 69-76. 

Details on the mechanisms and theories of excitation energy transfer via dipole-dipole interaction (FRET Forster resonance energy transfer) and via exchange interaction (Dexter s mechanism) can be found in B. Valeur, Molecular Fluorescence. Principles and Applications, Wiley-VCH, Weinheim, 2002, chap. 4 and 9. 

Mechanism of CL enhancement. According to Forster s theory, energy transfer is a distance dependent interaction between the different electronic excited states of molecules in which excitation energy is transferred from one molecule (donor) to another molecule (acceptor). Fig. 3 shows that fluorescence of HSA at 348nm decreased with increasing FCLA concentration. The energy from excited-state HSA maybe be transferred to FCLA or be lost in a non-radiative manner. 

When one metal ion plays the role of a donor for sensitizing the emission of a second accepting metal ion, the characteristic lifetimes T of their excited states, which are related to their deactivation rates by em = ( em) / are affected by the intermetallic communication process (Figure 122). If the energy transfer rate is much faster than the deactivation rate of the donor ion, the situation is very simple and assuming a Forster s dipole-dipolar mechanism, the yield of the transfer is given similarly to Eq. (77) by... 

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