Energy migration and transfer

Many charge-transfer complexes do not fluoresce. Thus, fluorescent probes, either as donor or acceptor, cause fluorescence quenching proportional to the association constant Kc of the complex. Fluorescence quenching may be utilized in the study of small molecules, as well as, particularly, macromolecules, to determine energy migration and transfer [78,79]. The fluorescence yield of the acceptor alone (F0), and that in the presence of... 

Electronic energy transfer from an excited state donor to a suitable acceptor is a fundamental process in photochemistry and is of prime importance in artificial photosynthesis. A variety of mechanisms exist by which energy migration and transfer can take placeand such processes have been used to create the so-called antenna effect . In particular, much research has concentrated on designing molecular systems in which an organic host is used to bind a lanthanide cation in such a way that photoexcitation of the host results in intramolecular energy transfer to the bound cation. ... 

Clearly, this is a simplistic view, since there is a considerable variation in 0g among the PS homopolymers. Yet the excimer fluorescence to fluorescence ratio in DMM solutions is very similar from polymer to polymer. A possible alternative, or additional, route to chain scission may involve intramolecular triplet energy migration and transfer processes. It has been shown (J ) that intramolecular triplet migration is facile in both PS and P(S-alt-MMA), but that sequences of two or more MMA-units interrupt the migration process. If an excited triplet trapping site can release its excess energy without bond scission,... 

Direct evidence of energy migration in the different films was found in polarized fluorescence emission studies. The fluorescence anisotropy indicated that intramolecular energy migration (with a Dexter hopping mechanism) existed in both the solution and spin-cast films. Further energy migration and transfer studies were... 

There are still more excellent examples of the energy migration and energy transfer processes in the literature. They have not been included here due to the authors limited reading and capability and the scope of this chapter. However, from the above discussion, it can be concluded that the energy migration and transfer processes in the conjugated polymers are very complicated. 

Triplet-energy migration and transfer processes have been studied to some extent. The efficiency of the decay of the triplet-triplet of excited poly(2-vinylnaphthalene) by an added quencher, piperylene, has been found to decrease with an increase in the molecular weight of the polymer. An increase in the... 

FIGURE 10. Schematic diagram showing energy migration and transfer in polymer chain [after figure in Pure Appl. Chem., 39, 265 (1974)]. 

Fig. 31 Schematic representation of the artificial photosynthetic reaction center by a monolayer assembly of antenna (H) and A-S-D triad molecules for light harvesting, energy migration and transfer, and charge separation via multistep electron transfer.

Ghiggino KP, Haines DJ, Smith TA, and Wilson GJ. Energy migration and transfer in styrene-containing polymers with inhibited excimer formation. Can. J. Chem. 1995 73 2015-2020. 

Further evidence for these proposals has been obtained through the study of the intramolecular quenching of phenanthryl fluorescence in 9-phenanthrylmethyl methacrylate / 9-anthrylmethyl methacrylate copolymers [95,97], The analysis is facilitated by the monoexponential decay of phenanthrene emission in the absence of intramolecular quenchers consequent upon the lack of excimer formation in this system. Under conditions of reasonably high trap concentrations, the decay curves became non-exponential (as is to be expected in the presence of energy migration and transfer of extents such that neither dominates the overall trapping kinetics). 

Photoexcited electronic energy migration and transfer phenomena in polymers are important if one is to understand photodegradation and photostabilization of polymers from a practical perspective. The phenomena are also critical in the photon-harvesting system for natural photosynthesis. For both practical and scientific interests, the energy migration and its transfer in... 

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