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Issue 4, 2013
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Unusual location of the pyrene probe solubilized in the micellar solutions of tetraalkylammonium perfluorooctanoates

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Abstract

The aqueous solutions of tetraalkylammonium perfluorooctanoates (C7F15COON(CnH2n+1)4, n = 1, 2, 3, 4, abbr. TMAPFO, TEAPFO, TPAPFO, TBAPFO) were studied by steady-state and time-resolved fluorescence with pyrene as a probe, and the ammonium perfluorooctanoate (APFO) was also studied as a comparison. Unusual response of pyrene fluorescence was observed. The intensity ratio of the first and third vibronic peaks of pyrene (I1/I3) greatly varied with the counterions for these fluorinated surfactants after their critical micelle concentration (cmc): for TEAPFO, the I1/I3 abnormally increased to a value higher than that of water, while for TBAPFO the I1/I3 value exhibited a small extent of decease after cmc. However, no significant change of I1/I3 was observed during the micellization of TMAPFO and TPAPFO. The lifetime of pyrene fluorescence (τ0) among the systems of tetraalkylammonium perfluorooctanoates (TAAPFOs) was observed to be increased with the hydrophobicity of counterions. Moreover, the time-resolved fluorescence decay curves of pyrene for all micellar solutions exhibited single exponential decay, suggesting a single environment for pyrene, i.e. each surfactant had a single location of pyrene solubilized in its micelle. The performances of the pyrene probe in concentrated solutions of neat ammonium/tetraalkylammonium chlorides (NH4Cl/TAACls) were also investigated and an unusually high I1/I3 could be found for tetraethylammonium chloride. It reached a conclusion that pyrene located in the counterion layer of the TAAPFO micelles, which could be ascribed to the hydrophobic interaction and cation–π interaction between pyrene and tetraalkylammonium ions (TAA+) and the immiscibility between pyrene and the fluorocarbon core.

Graphical abstract: Unusual location of the pyrene probe solubilized in the micellar solutions of tetraalkylammonium perfluorooctanoates

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Publication details

The article was received on 05 Sep 2012, accepted on 07 Nov 2012 and first published on 23 Nov 2012


Article type: Paper
DOI: 10.1039/C2SM27057A
Soft Matter, 2013,9, 1164-1171

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    Unusual location of the pyrene probe solubilized in the micellar solutions of tetraalkylammonium perfluorooctanoates

    H. Xing, P. Yan and J. Xiao, Soft Matter, 2013, 9, 1164
    DOI: 10.1039/C2SM27057A

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