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|Type:||Artigo de periódico|
|Title:||Electronic Excitations And Alternation Of Conjugated Polymers|
|Abstract:||The electronic excitations and fluorescence of conjugated polymers are related to large or small alternation δ of the transfer integrals t(1 ± δ) along the backbone. The fluorescence of polysilanes (PSs) and poly (para-phenylenevinylene (PPV) is linked to large δ, which places the one-photon gap Eg below the lowest two-photon gap Ea and reduces distortions due to electron-phonon (e-p) coupling. In contrast to small δ ∼ 0.1 in π-conjugated polymers, such as polyacetylene (PA), para-conjugated phenyls lead to an extended π-system with increased alternation, to states localized on each ring and to charge-transfer excitations between them. Surprisingly good agreement is found between semiempirical parametric method 3 (PM3) bond lengths and exact Pariser-Parr-Pople (PPP) π-bond orders for trans-stilbene, where the PPV bipolarons are confined to two phenyls. Stilbene spectra are consistent with increased alternation and small e-p distortions. © 1993.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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