Foster energy transfer

The energy E in Equation 6.86 has been replaced by the frequency v (in cm-1), FA E) has been replaced by the extinction coefficient sA v) of the acceptor, (pp is the fluorescence quantum yield, and k2 2/3 is an orientation factor. An expression similar to Equation 6.87 was deduced by Foster using a simpler mechanism of the energy transfer.41 The rate constant deduced from the dipole-quadmpole interaction is given in Equation 6.88, where a 1.266 and other parameters and functions are as defined above. 

If polyatomic vibrational relaxation really takes place in this fashion, many of the same kinds of mechanistic questions we have posed for diatomics will obviously become much richer when posed for polyatomics Which particular solvent motions will serve to foster IVR Will some motions actually interfere with IVR Does solvent dynamics play a role in deciding between alternative routes for intramolecular energy transfer Although the specific issues are different from those in this chapter, there is no conceptual barrier to pursuing them with the same techniques. Indeed, our preliminary investigations indicate that many of these questions should be perfectly amenable to the kinds of approaches we have been discussing. 

For energy transfer to occur from the excited chromophore (donor) to the quencher Q (acceptor), the latter must have lower energy states than the donor. The transfer can take place by two processes (1) long-range energy transfer or Foster mechanism and (2) contact, or collisional, or exchange energy transfer. 

The transfers that take place by mechanism 1 are limited by diffusion of molecules in solution and should be affected by the viscosity of the medium. Transfers by mechanism 2, on the other hand, should be much less sensitive to the viscosity of the medium. It was shown by Foster [86] that the rate constant of resonance-energy transfer (mechanism 1), as a function of distance, is ... 

The intramolecular distance r can be estimated by measuring singlet-singlet energy transfer using the Foster equation ... 

Scheme 2. In this photophysical scheme it was proposed that M, and D interact by the generally accepted exciton diffusion mechanism. M was considered to be an isolated naphthalene chromophore which can transfer energy into M with a transfer rate characterized by the rate coefficient kt- Reverse transfer from M to M was considered unimportant for the following reason. Exciton diffusion is expected to be very efficient within sequences of naphthalene chromc hoies within the chain comprising the M sites. In view of the reduced lifetime of M relative to M and of the delocalised nature of the enei within extended chromophore sequences which increases the effective s aration of M and M, Mf to M energy transfer by Foster or Dexter mechanisms is diminidied relative to the M to M process.

The new generation of FRET utilizes a scheme of two-tiered energy transfer in two different time scales. First, a regular fluorophore which absorbs ultraviolet light for excitation, and emits with nsec lifetime, transfers its energy in the nsec timeframe to a lanthanide ion, for example, Eu(3+), via the nonradiative Foster... 

SNR s fluidized-bed cogeneiation system is an early example of the commercial development of AFBC technology. Foster Wheeler designed, fabricated, and erected the coal-fired AFBC/boHer, which generates 6.6 MWe and 37 MW thermal (also denoted as MWt) of heat energy. The thermal energy is transferred via medium-pressure hot water to satisfy the heat demand of the tank farm. The unit bums 6.4 t/h of coal and uses a calcium to sulfur mole ratio of 3 to set the limestone feed rate. The spent bed material may be reiajected iato the bed as needed to maintain or build bed iaventory. The fly ash, collected ia two multicyclone mechanical collectors, may also be transferred pneumatically back to the combustor to iacrease the carbon bumup efficiency from 93%, without fly ash reiajection, to 98%. 

Th. Foster, Delocalized Excitation Excitation Transfer, Bulletin No. 18, U.S. Atomic Energy Commission, Florida State Univ. (1965). 

Table 2. These methods, which expand the range of conditions under which reactions have been studied, have helped provide new insights into chemical reactivity, the role of internal energy in fostering reactivity, and the transfer of energy in molecular systems.

Electronic properties of chlorophylls and related systems are of fundamental interest to understand the molecular mechanisms of energy and charge transfer in complex antenna and photosynthetic reaction centers [104]. Several studies were dedicated to investigate the electronic absorption spectra of photosynthetic chromophores (see Konig and Neugebauer [105] for a recent review). Most of the available experimental information on the electronic properties of chlorophylls is determined in solution. This feature fostered theoretical studies on the electronic properties of photosynthetic chromophores in solution, [106-114] or in interaction with hydrogen bonding species, [113, 115-122] or with the protein environment [123, 124]. 

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