Electronic energy transfer trivial

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... 

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. 

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. 

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. 

The intermolecular transfer of electronic excitation energy is a common phenomenon in photochemistry. It is called photosensitization and may occur by a number of mechanisms, both radiative and nonradiative. In the radiative process, also called the trivial mechanism, the acceptor, A, absorbs a quantum emitted by a donor, D (Equations 13.11 and 13.12). 

A sensitizer is of paramount importance to photovoltaic performance. The sensitizer is attached to the surface of a mesoporous wide band-gap semiconductor serving as electron transporter. While the trivial ultraviolet absorption for 375 with a molar extinction coefficient (s) of 50.0 x 103 M [ cm-1 peaks at 372 nm, the s value of its low-energy band at 525 nm (mainly stemming from the intramolecular charge transfer transition) is 44.8 x 103 IVT1 cm-1 (08JA9202). 

The reduction half-reaction is an easy two-electron transfer reaction, while four electrons are involved in the oxidation of water to form oxygen. While by no means trivial, it is considerably easier to photo-oxidize water than it is to photoreduce CO2. Moreover, hydrogen can be readily converted into electricity - and back again - with fuel cells and electrolyzers. This offers the prospect of a future energy infrastructure based oti sunlight, hydrogen, and electricity, as illustrated in Fig. 1.2. 

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