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On the apparent fluorescence recovery due to electrosorption

TitleOn the apparent fluorescence recovery due to electrosorption
Publication TypeJournal Article
Year of Publication2003
AuthorsShepherd, JL, Bizzotto, D
JournalJournal of Physical Chemistry B
Volume107
Pagination8524-8531
Date PublishedAug
Type of ArticleArticle
ISBN Number1520-6106
KeywordsADSORPTION, CYANINE DYES, DYNAMICS, INSOLUBLE SURFACTANT, microscopy, MONOLAYERS, OCTADECANOL, RESONANCE ENERGY-TRANSFER, SILVER-ISLAND FILMS, VOLTAGE-SENSING DYES
Abstract

Unusual fluorescence characteristics of a carbocyanine dye/octadecanol layer adsorbed onto a Au(111) electrode surface are described. The potential of the electrochemical interface controls the distance separating a previously adsorbed organic layer and the metal electrode by way of a unique adsorption/desorption process. The behavior of the fluorescent-labeled organic layer was monitored under full potential control with epi-fluorescence microscopy and image analysis. For an adsorbed layer, fluorescence is quenched by nonradiative energy transfer into the metal. When desorbed, intense fluorescence was observed due to the separation of the surfactant from the metal surface. In this desorbed state, the surfactant displayed a strong decay in fluorescence intensity with time (loss of 90% over 20 min). We describe two parallel pathways for this fluorescence decay: irreversible photodestruction of the carbocyanine fluorophore and reversible fluorophore aggregation resulting in a decrease in monomer fluorescence. Readsorption of the surfactant layer onto the metal electrode resulted in a near total (85%) recovery of fluorescence measured after desorption of the surfactant layer. The readsorption of the organic monolayer onto the electrode was believed to convert the nonfluorescent aggregates back to the monomer form. These observations were made possible due to the control of the distance separating the fluorescent-labeled organic layer from the metal afforded by the electrical variable.

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