Lowest conjugated chains

According to a large number of experimental studies, the most stable phologen-erated species in the lowest excited stales of conjugated chains are electron-hole pairs bound by Coulomb attraction and associated to a local deformation of the backbone, i.e., polaron-excilons [18]. A good insight into the properties of these species can be provided by quantum-chemical calculations our recent theoretical... 

The class of compounds that has been most extensively investigated from the point of view of two-photon absorption is that of so-called quadrupolar chromophores. hi essence, these molecifles are linear conjugated chains with electron donating or withdrawing substituents arranged symmetrically with respect to the center of the molecifle (Fig. 8, classes I-IV). With the inversion center being preserved, the lowest order moment supported by these molecules is the quadrupole moment. 

Figure 4-6. Evolution of the INDO/SCI-calculalcd. splitting between the lowest two oplieal transitions of cofacial dimers formed by two PPV chains as a function of the inverse number of bonds (1/u) along the conjugated backbone of the oligomer. The theoretical results are reported for interchain distances of 4 A (open circles) and C> A (tilled circles).

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