Energy transfer electronic, intermolecular

The nomenclature relating to electronic energy transfer is such that it is named according to the multiplicity of D and A as D —A energy transfer, common examples being  

Since the excited-state donor molecules are initially produced by photoexcitation and the energy is transferred to A, energy transfer is also referred to as the photosensitisation of A or the quenching of D.  

Nonradiative energy transfer has a major role in the process of photosynthesis. Light is absorbed by large numbers of chlorophyll molecules in light-harvesting antennae and energy is transferred in a stepwise manner to photosynthetic reaction centres, at which photochemical reactions occur. This fundamental energy-transfer process will be considered in more detail in Chapter 12. 

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C. Intermolecular Electronic Energy Transfer Quenching of one excited-state species may result in transfer of electronic energy to the quenching species. Intermolecular energy transfer has become an important technique in photochemistry because it often permits the selective population or depopulation of one specific excited-state species. 

Figure 6.17 Intermolecular electronic energy transfer. Emission spectra of biacetyl solutions in aerated hexane containing increasing concentrations of benzene. All solutions contain 0.005 M biacetyl. Exciting wavelength 265 nm. See text. From Ref. [34,g].

The decrease of the fluorescence intensity by interaction of the excited state of the fluorophore with its surroundings is known as quenching (not random ptrocess). The intermolecular electronic energy transfer is the possible way of RTIL fluorescence quenching ... 

The next important phenomena that the result of supramolecular effect are the concentration and proximity effects concerning the components of analytical reaction, even through they are considerably different in hydrophobicity, charge of the species, complexing or collisional type of interaction. The concentration and proximity effects determine the equilibrium of analytical reaction, the efficiencies of intramolecular or intermolecular electronic energy or electron transfer and as a result the sensitivity of analytical reactions. 

Clarke (326) has studied the optical electron spin polarization in triplet anthracene and has observed ESR emission at 1.5°K which was attributed to a non-Boltzman distribution over the triplet spin levels at low temperature. The dynamics of optical spin polarization in triplet naphthalene at 1.6°K was also reported by Sixl and Schwoerer (327a) and van der Waals et al. (327b). have used a general method to study dynamics of populating and depopulating triplet spin levels by microwave-induced delayed phosphorescence. These experiments enable measurements of the lifetimes of each triplet spin state and thus can provide important information about intramolecular decay processes and intermolecular triplet energy transfer. 

THE USE OF INTERMOLECULAR DISTANCES BETWEEN ADSORBATES AS YARDSTICKS ELECTRONIC ENERGY TRANSFER (34). 

Direct intermolecular electronic-eneigy transfer was first observed in this way in the gas phase, in a mixture of mercury and thallium vapours (G. Cario and J. Franck, Z Physik 17 (1923) 202). An instance of the phenomenon in solution was reported by Th. FSrster in Aim. Phys. 1 (1948) 55 Z Elektrochem. 53 (1949) 93. It is often called sensitised fluorescence . It is a case of non-radiative energy transfer, by contrast with radiative transfer in which a photon is emitted by one molecule and absorbed by another (A - A + /iv )n> + B -> B). The latter type of transfer gives little information on molecular interactions indeed the A and B molecules need not even be in the same vessel. It is of great practical importance, however, notably in photosynthesis, which makes use of photons emitted from the sun (Section 4.3.6.1). 

An electronic energy transfer process is the one-step transfer of electronic excitation energy from an excited donor molecule (D ) to an acceptor molecule (A) in separate molecules (intermolecular energy transfer) or in a different part of the same molecule (intramolecular energy transfer) [863,867, 1766, 1804, 2161, 2162, 2220]. 

Dissociation of the molecule, usually into radicals Intermolecular energy transfer giving another electronically exited species, which may undergo reaction Luminescenee ineluding phosphorescence and fluorescence... 

One striking prediction of the energy gap law and eq. 11 and 14 is that in the inverted region, the electron transfer rate constant (kjjj. = ket) should decrease as the reaction becomes more favorable (lnknr -AE). Some evidence has been obtained for a fall-off in rate constants with increasing -AE (or -AG) for intermolecular reactions (21). Perhaps most notable is the pulse radiolysis data of Beitz and Miller (22). Nonetheless, the applicability of the energy gap law to intermolecular electron transfer in a detailed way has yet to be proven. 

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