Molecular excitons

Primary Photoexcitations in Conjugated Polymers Molecular Exciton versus Semiconductor Band Model (Ed. N.S. Sariciftci) World Scientific, Singapore 1997. 

In a regime of strong interaction between the chains no optical coupling between the ground slate and the lowest excited state occurs. The absence of coupling, however, has a different origin. Indeed, below 7 A, the LCAO coefficients start to delocalize over the two chains and the wavefunclions become entirely symmetric below 5 A due to an efficient exchange of electrons between the chains. This delocalization of the wavcfunclion is not taken into account in the molecular exciton model, which therefore becomes unreliable at short chain separations. Analysis of the one-electron structure of the complexes indicates that the... 

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

In a metal, there are excited states for electrons that lie below the ionization energy. This can be conceived as an electron in a "conduction band" and a "hole" that interact so that the combination is neutral but not of lowest energy. Such an excited state is called an exciton. Excitons may move by diffusion of the electron-hole pair or by transfer of a molecular exciton to another molecule. Reversion of the exciton to a lower energy state may be slow enough for the lifetime to be longer that of lattice relaxation processes. 

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

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

Kasha M (1976) Molecular excitons in small aggregates. In Di Bartolo B (ed) Spectroscopy of the excited state. Premium, New York, pp 337-363... 

Kasha M (1963) Energy transfer mechanisms and the molecular exciton model for molecular aggregates. Radiat Res 20 55-71... 

Sariciftci NS (1997) Primary photoexcitations in conjugated polymers molecular exciton versus semiconductor band model. Word Scientific, Singapore... 

Figure 7. Decays of photoinduced absorption in sexithienyl at pump intensities Io and Io/2 (picosecond range). Bi-molecular exciton-exciton annihilation is evidenced [21].

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

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-... 

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