Importance of Electrostatic Interactions in The Mobility of Cations in Nafion

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• 作者：E Siva Subramaniam Iyer ; Anindya Datta
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：July 14, 2011
• 年：2011
• 卷：115
• 期：27
• 页码：8707-8712
• 全文大小：877K
• 年卷期：v.115,no.27(July 14, 2011)
• ISSN：1520-5207

文摘

A molecular level understanding of the mobility of cations in the Nafion membrane has been attempted, using the excited state proton transfer (ESPT) process in the fluorescent probe Coumarin 102. ESPT is hindered significantly upon decreasing the water content. Using TRANES (time-resolved area normalized emission spectroscopy), the evolution of the ESPT state is clearly observed over hundreds of picoseconds in lower water content, implying that ESPT is hindered even in the nanovolume probed by the dye. Most remarkably, in the partially dried membrane, the predominant fluorescent species is the zwitterionic form, generated by excited state deprotonation of the cationic form. This implies that the molecule loses a proton from its nitrogen center in the excited state, as usual, but cannot recapture it readily at the oxygen center, at low water contents. This phenomenon is rationalized in light of an increased electrostatic attraction that is experienced by cations upon drying.