Excited molecule intramolecular energy transfer

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]. 

Extrusion or elimination of small stable species such as CO2 Intramolecular energy transfer Quenching involving translational or vibrational excitation of another molecule... 

It is often possible to describe the photoexcitation of a molecule in terms of a localized excitation, e.g., excitation of the 0=0 group of a ketone. In most photochemical decompositions the bond that breaks and leads to fragmentation is not the same as the site of localized excitation.165 Therefore, it is necessary to consider the mechanism of intramolecular energy transfer as part of the photochemical reaction. 

The situation is different from that with the intramolecular energy transfer catalyzed by solute encounters. If an active molecule with two excited states, A and B, say, singlet and triplet, meets quencher C considered as structureless but carrying heavy atom (halogen substituent), then the latter catalyzes the... 

Thus, in discussing the degree of solvation needed to stabilize the excited state intramolecular electron transfer for DMABN in condensed phases, one must realize that only one polar solvent molecule, properly placed, will lower the energy of this state below that of the local nn excited state (see Grassian et al. 1989,1990 Shang and Bernstein 1992 Warren et al. 1988 for more discussion of this point). 

The efficiency of intramolecular energy transfer has been studied in certain molecules which consist of two independent systems of conjugated double bonds separated by up to three saturated carbon atoms.4882,94 Only the lowest states of any multiplicity were found to emit. Thus although the absorption spectrum of such a species consists of a superposition of characteristic absorption due to the separate conjugated groups, fluorescence and phosphorescence from only one group are observed even when the other group is excited. Further studies... 

The transfer of electronic energy (and excitation) between two different molecules (intermolecular energy transfer pathway iv of Fig. 1) or between two different electronic states (intramolecular energy transfer pathway v) plays a central role in photochemistry. The equivalent processes involving electrons, in which charge is transferred to a different molecule, or is moved in position in one molecule, may also be promoted photochemically. These processes are explored in the present section. 

It is instructive to examine a zeroth-order calculation of intramolecular energy transfer in a model molecule in which the energies of the vibrational and rotational modes are conserved separately, in which the initial excitation of the van der Waals stretching mode is zero (n = 0), and in which the initial values of... 

R.B. Gerber, V. Buch and M.A. Ratner, Time-dependent self-consistent field approximation for intramolecular energy transfer. I. Formulation and application to dissociation of van der Waals molecules, J. Chem. Phys., 77 (1982), 3022 M.A. Ratner and R.B. Gerber, Excited vibrational states of polyatomic molcecules the semiclassical self-consistent field approach, J. Phys. Chem., 90 (1986) 20 R.B. Gerber and M.A. Ratner, Mean-field models for molecular states and dynamics new developments, J. Phys. Chem., 92 (1988) 3252 ... 

The direct irradiation at 254 nm of the allenes (67) in hexane gives the molecule in its triplet state. Bridging within this state affords the intermediate biradical (68). Bond formation then yields the major products (69) and (70). Minor products (71) and (72) are also formed. Irradiation at X. > 280 nm fails to yield products. However, acetophenone sensitization is effective. The authors suggest that in this instance the vinyl moiety is the chromophore which is excited and that intramolecular energy transfer is involved. The yields obtained from the reactions are shown in Table 1. 

COLLISION-INDUCED INTRAMOLECULAR ENERGY TRANSFER IN ELECTRONICALLY EXCITED POLYATOMIC MOLECULES... 

The title of this chapter seems to promise a general discussion of the nature of collision-induced intramolecular energy transfer in electronically excited polyatomic molecules. If interpreted as just stated, the title promises more than can be delivered at this time. It is only recently that advances in experimental technique have permitted the study of the pathways of intramolecular energy redistribution following collision, and the few results now available were neither anticipated nor can they yet be fully accounted for by the available theories of collision-induced energy transfer. This chapter describes a preliminary synthesis of the limited experimental and theoretical information in hand and discusses some of its implications. It will be seen that more questions are raised than are answered. 

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