Charge-transfer exciton

Following the theory of exciton charge transfer between molecular dimmers [14] we now write the frequency of transfer between the two states as... 

At finite separations, these four zero-order terms interact pairwise and produce states S, S, I, and I of strongly mixed exciton-charge-transfer character, where the VB functions are ionic and contain terms such as... 

Charge transfer from the 11 Bu to an adjacent molecule or segment of a chain, i.e., dissociation of the 11 Bu. This process may also be extremely fast.24 Indeed, so fast that it has been suspected that this charge transfer state, aka a spatially indirect exciton, charge transfer exciton (CTE), or intermolec-ular or interchain polaron pair, may be generated directly from the ground state.24... 

The excitation energies of bulk transitions of the band-to-band type in oxides indeed show to correlate well [54] with the hardness of the oxide cations [11] (see Fig. 2). Experimental evidence for local charge transfer properties (softnesses) may come from the measurement of electronic transitions of the excitonic charge-transfer type, during which electron density is transferred from an oxygen ion to its immediate surroundings. These have been observed in UV-DRS spectra for a series of alkaline-earth oxides [54]. 

Open symbok excitonic charge transfer transitions... 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

Bittner ER (2006) Lattice theory of ultrafast excitonic and charge-transfer dynamics in DNA. 

Not all sensitized photochemical reactions occur by electronic energy transfer. Schenck<77,78) has proposed that many sensitized photoreactions involve a sensitizer-substrate complex. The nature of this interaction could vary from case to case. At one extreme this interaction could involve a-bond formation and at the other extreme involve loose charge transfer or exciton interaction (exciplex formation). The Schenck mechanism for a photosensitized reaction is illustrated by the following hypothetical reaction ... 

We note at this point that, when the two fragments become identical, the charge transfer configurations and the locally excited configurations will have to be replaced by charge-resonance and exciton-resonance configurations, respectively. 

Optical Absorption Spectra and Electronic Structure The optical spectra of all the doubledeckers are listed in Table I, On first glance, Ce(0EP)2 has a "normal" spectrum (7), However, the spectrum shows extra bands and therefore should be called "hyper", A small band appears at 467 nm (maybe a ligand-to-metal charge transfer band), and broad features extend far into the near infrared (NIR), The latter absorption may be due to exciton interactions. Contrary to the known rare earth monoporphyrins (7), it has been shown for the closely related cerium(IV)... 

Dimerization causes shifts of optical absorption and emission bands of the order of several hundred cm (cf. Table I). This suggests that the triplet EPR data must be interpreted in terms of exciton and charge transfer effects. In the case of ZnTCP the effect of dim.erization on zfs values can be accounted for on the basis of rapid triplet excitation transfer between essentially unperturbed porphyrin moieties. If the exciton model applies the principal components of the zfs tensor in the dimer (X, , Z ) can be related... 

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