Trivial energy transfer

Energy transfer by the trivial mechanism is characterized by (a) change in the donor emission spectrum (inner filter effect), (b) invariance of the donor emission lifetime, and (c) lack of dependence upon viscosity of the medium. 

If the energy is transferred by trivial emission/reabsorption, it will lengthen the measured lifetime of the donor emission, not shorten it as happens in resonance energy transfer. This comes about because intervening absorption and emission processes take place prior to the final fluorescence emission (the reabsorption cannot take place until the photon has been emitted) the two processes do not compete dynamically, but follow in a serial fashion. In FRET, such an emission/reabsorption process does not occur, and the fluorescence lifetime of the donor decreases. This is an experimental check for reabsorption/reemission. 

For the fate of the excited states in condensed media, we must add to this list energy transfer processes. These are broadly classified as radiative (or trivial ), coulombic (mainly dipole-dipole interaction), or electron-exchange processes. 

Forster (1959) classifies the qualitative features based on which one can distinguish the various modes of energy transfer. Mainly, only collisional transfer depends on solvent viscosity (vide infra), whereas complexing between the donor and acceptor changes the absorption spectrum. On the other hand, the sensitizer lifetime decreases for the long-range resonant transfer process, whereas it should be unchanged for the trivial process. 

Preparing isotopically enriched carbonyls and related species is not always a trivial problem. We have recently developed (20) a method which looks particularly promising in some cases. CW CO2 laser irradiation of a gas phase mixture containing SF5 as an energy transfer agent can promote thermal chemistry without complications due to wall reactions, e.g. 

Energy-transfer processes in which free photons exist as intermediates are sometimes referred to as trivial transfer mechanism. This term is misleading in the sense that such processes (e.g., in combination with internal reflection) can cause very complex and interesting phenomena [61, 65-67]. Radiationless energy-transfer processes have been studied extensively since the pioneering work of Forster [68, 69] and Dexter [70] (see, e.g., [40, 67, 71-73]). Here, we concentrate on the description of one-photon events, specifically with respect to radiationless energy-transfer processes. 

Resonance energy transfer between the aromatic amino acids proceeds by very weak coupling between the donor and acceptor.151,52) Very weak coupling implies that the interaction between the donor and acceptor wave functions is small enough so as not to perturb measurably the individual molecular spectra. This transfer process, which is distinct from the trivial process of absorption of an emitted photon, involves radiationless deexcitation of an excited-state donor molecule with concomitant excitation of a ground-... 

The nonradiative energy transfer must be differentiated from radiative transfer which involves the trivial process of emission by the donor and subsequent absorption of the emitted photon by the acceptor ... 

In fluid solutions only the third mechanism is of importance in transfer of triplet excitation. The trivial mechanism is usually excluded because most molecules do not phosphoresce in solution, and the second mechanism seems to be excluded because the transition moments for the T - S process in the donor and the T - S transition of the acceptor should both be vanishingly small. An interesting possibility which has yet to be explored experimentally is that heavy atom-containing solvents might so enhance T <- S transition probabilities that long-range triplet energy transfer may become important. 

When deciding to study the dynamics of electronic excitation energy transfer in molecular systems by conventional spectroscopic techniques (in contrast to those based on non-linear properties such as photon echo spectroscopy) one has the choice between time-resolved fluorescence and transient absorption. This choice is not inconsequential because the two techniques do not necessarily monitor the same populations. Fluorescence is a very sensitive technique, in the sense that single photons can be detected. In contrast to transient absorption, it monitors solely excited state populations this is the reason for our choice. But, when dealing with DNA components whose quantum yield is as low as 10-4, [3,30] such experiments are far from trivial. 

The SA expression (3.186) coincides with its IET analog KAB only in the trivial case of irreversible energy transfer (k, = 0) when Q= ( + and the... 

There is a third mechanism of energy transfer known as the trivial or radiative energy-transfer mechanism. Here, energy is transferred by radiative deactivation of a donor and reabsorption of this emitted light by an acceptor molecular entity. This mechanism is less important in supramolecular chemistry and is not dealt with in further detail here. 

A quencher should have an excitation energy lower than that of the donor species and the appropriate electronic configuration. Transfer of excitation energy proceeds by radiative or radiationless deactivation of the donor molecular entity. Radiative energy transfer (also called trivial energy transfer) consists of light emission by the donor molecule and reabsorption of the emitted light by the acceptor molecular entity. 

Several different mechanisms of electronic energy transfer are believed to operate under different circumstances. The first of these is the so-called trivial mechanism of radiative transfer, which can be represented by the processes... 

Trivial energy transfer Same as radiative energy transfer. 

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