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摘要
The behavior of intrinsic trace aggregate species based on pi-pi stacking in conjugated polymer and its influencing factors are significantly important for the color purity and stability of polymer light-emitting diodes. In this work, low-energy emission has been observed in the aggregate state of meta-linked polymer poly(9,9'-spirobifluorene-3,6-diyl). The origin of low-energy emission has been testified as an excimer emission because the absorption spectra for a well-dissolved dilute solution and that of the aggregated state are quite similar in shape, and the concentration/solvent dependence of low-energy emission in emission spectra is well consistent with character of an excimer. The excimer emission is only observed in meta-linked polymers but not para-linked ones, which indicates the importance of meta-linkage and the corresponding conformation in the formation of an excimer. The meta-linkage effectively broke the conjugation, which allows a fluorene segment as the excimer building block in the polymer, and induces chain distortion, where interchain interaction is not restrained by an adjacent fluorene segment. Especially when the adjacent 9-positions of fluorenes are in the same side of the backbone (defined as cis-conformation), local big chain distortion tends to induce a more effective segment interaction.
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