Spectroscopic Properties, Excitation, and Electron Transfer in an Anionic Water-Soluble Poly(fluorene-alt-phenylene)-perylenediimide Copolymer

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• 作者：Ana T. Marques ; Hugh D. Burrows ; J. S茅rgio Seixas de Melo ; Artur J. M. Valente ; Lic铆nia L. G. Justino ; Ullrich Scherf ; Eduard Fron ; Susana Rocha ; Johan Hofkens ; Edward W. Snedden ; Andrew P. Monkman
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：June 28, 2012
• 年：2012
• 卷：116
• 期：25
• 页码：7548-7559
• 全文大小：607K
• 年卷期：v.116,no.25(June 28, 2012)
• ISSN：1520-5207

文摘

An anionic fluorene-phenylene poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}-based copolymer containing on-chain perylenediimine (PDI) chromophoric units, PBS-PFP-PDI, was synthesized and its photophysical properties studied as aggregates and isolated chains in water and dioxane/water (1:1) solution. UV鈥搗is and emission spectroscopy measurements, time-correlated single photon counting, and wide field imaging have been employed to investigate the excited-state behavior of the PBS-PFP-PDI copolymer, including the effect of environment on the energy and electron transfer to the on-chain PDI chromophore. Although the F枚rster overlap integral is favorable, no evidence is found for intramolecular singlet excitation energy transfer in isolated copolymer chains in solution. Fluorescence is suggested to involve an interchain process, thus revealing that isolated copolymer chains in solution do not undergo efficient intramolecular energy transfer. However, quenching of the PBS-PFP excited state by PDI is observed in aqueous media and ultrafast pump鈥損robe studies in water or dioxane鈥搘ater solutions show that electron transfer occurs from the phenylene-fluorene units to the PDI. The extent of electron transfer increases with aggregation, suggesting it is largely an interchain process. The interaction of the negatively charged PBS-PFP-PDI copolymer with the positively charged surfactant hexadecyltrimethylammonium bromide (CTAB) in solution has also been studied. The copolymer PBS-PFP-PDI aggregates with the surfactant already at concentrations below the critical micelle concentration (cmc) and the nonpolar environment allows intermolecular energy transfer, observed by the weak emission band located at 630 nm that is associated with the emission of the PDI chromophore. However, the fact that the PDI photoluminescence (PL) lifetime (1.4 ns) obtained in the presence of CTAB is considerably shorter than that of the nonaggregated chromophore (5.4 ns) suggests that even in this case there is considerable PL quenching, possibly through some charge transfer route. The increase of the PBS-PFP-PDI photoluminescence intensity at surfactant concentrations above the cmc indicates deaggregation of polyelectrolyte within the initially formed polyelectrolyte鈥搒urfactant aggregates.