Molecular exciton theory

Figure 2. Molecular orientation model of bilayer membranes and schematic explanation of Kasha s molecular exciton theory (see equation (2)).

The conjugated systems in Fig. 2 have inversion and e-h symmetry. The acenes are the prototypical systems of molecular exciton theory[23]. The photophysics of stilbene and polyparaphenylene vinylene (PPV) have been extensively studied [14], separately at first and together since the preparation [24] of light-emitting diodes based on PPV. Pyrene and perylene appear in many contexts, while the polydiacet-... 

The first improved theory addressing the weakly coupled, or non-adiabatic electronic excitation transfer was the semiclassical vector model proposed by Forster [15]. It was further developed and refined by Levinson [16], Kasha [17], and others [18], who sometimes referred to it as the molecular exciton theory . Notably, this was the first successful attempt to link the rate of electronic excitation transfer with readily available experimental parameters, such as the absorption spectrum of the... 

In order to proceed it is now necessary to consider the nature of the lowest excited state of these polymers. One description which appears to be particularly appropriate to these materials is that given by the molecular exciton theory (37,38). This of course is suggested by the nature of the fluorescence spectrum itself and in addition this approach has proven to be quite successful in the Interpretation of the electronic states of the alkanes, the structural analogs of the poly(organosllylenes) ( 3, 6). The basic assumption... 

T. Eorster, Molecular Exciton Theory, Part III Editor O. Sinanou lu (Academic Press, New York, 1965). 

Distributed point-charge models may be constructed from FSGO-based wave-functions to provide accurate representations of electrostatic potentials and properties, while naturally preserving both total charge and dipole moment. Incorporation of such PCM s within molecular exciton theory provides an attractive and economical method for the study of spectral features of large molecular aggregates. 

LaLonde DE (1985) Evaluation of approximations in molecular exciton theory applications to photosynthetic systems. Thesis, University of Kansas, Lawrence, KS... 

Rapid convergence at large alternation is expected on general grounds. The sufficiency of N = 14 oligomers for linear or TPA spectra of Hubbard and PPP chains with 5 > 0.6 follows in detail from molecular exciton theory [116]. The different shapes of PPP and Hubbard crossovers in Fig. 6.15 are due to different B states, which are in turn related to Vpp- in Eq. (7) B is an exciton in PPP theory [134] and evolves [116] to an excited dimer at 5 = 1, while B is a CT state [37] in Hubbard chains at 5 1. These possibilities for B are another generic feature of Eq. (7). Molecular PPP parameters place [133] PA on the correlated side, PS and PPV on the band side. 

A strong intermolecular interaction among Jt-electron chromophores is observed as Davydov splitting in the absorption spectrum. Kasha proposed a molecular exciton theory for the strong n-n interaction in molecular aggregates, e.g., molecular crystals, and the spectral shift due to the Davydov splitting can be described as a function of chromophore orientation [35,36]. Due to the two-... 

Molecular exciton theory of a binary system with two chromophores. 

A.S. Davydov, Theory of Molecular Excitons, Plenum Press, New York 1971. 

Numerous studies of carotenoid aggregates have focused on the molecular organization of the aggregates (Simonyi et al. 2003), but little is known about aggregation-induced effects on carotenoid excited states. Classical exciton theory can qualitatively explain the aggregation-induced shifts of absorption bands (Section 8.3.1), but a detailed understanding of the parameters governing the... 

With the absorption of a quantum with an energy of more than 3.05 eV resp. 3.29 eV, an electron is lifted out of the valence band and into the conduction band, thereby forming an exciton (Fig. 5). This interpretation is also supported by the molecular orbital theory and the crystal field theory regarding the bonding conditions in the TiC lattice. 

Davydov AS (1968) Theory of molecular excitons. Nauka, Moskow... 

In this expression 1, m, n denote the direction cosines specifying the relative orientations of the principal axes in the monomer and dimer. (The expressions defining the values D and E are D = -3/2 Z and E = 1/2 (Y - X).) For the face-to-face structure proposed for [ZnTCP]2 (14) exciton theory predicts that dimerization should not affect the out-of-plane component (Z) of the tensor. The in-plane component, and therefore E, depends on the angle of rotation of one porphyrin plane relative to the other. According to the exciton model the observed reduction in E (cf. Table II) corresponds to an angle of rotation of about 23. This is reasonably close to the value predicted by molecular models (14). 

Craig, D. P., WalmsUy, S. H. Excitons in molecular crystals Theory and applications. London-New York Benjamin 1968. 

Consider, now, radiationless transitions in pure molecular crystals of aromatic molecules. At the very outset we must realize that crystal field effects may lead to the inversion of the order of the triplet and singlet exciton levels relative to the ordering of the corresponding molecular states.12 The Davydov tight binding formulation of exciton theory leads to the following representation for the manifold of optically accessible (k = 0) energy levels in a pure molecular crystal 138... 

Davydov, A. S. Theory of Molecular Excitons McGraw-Hill New York, 1962 174... 

Several theories have been developed to explain how energy absorbed by one molecule is transferred to a second acceptor molecule of the same or a different species. At first sight exciton theory,20 66 which accounts for excitation transfer in molecular aggregates or crystals and the Davydov splitting effects connected with it, appears to bear little relationship to the treatment of long-range resonance transfer as developed, for example, by Forster.81-32 However, these theories can be shown to arise from the same general considerations treated at different well-defined mathematical limits.33-79... 

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