| Abstract
| - The adsorption properties of ionic fluorescent dyes at the polarized water/1,2-dichloroethane interface werestudied by potential modulated fluorescence (PMF) spectroscopy under total internal reflection. Analysis ofthe frequency-dependent fluorescence associated with modulation of the interfacial concentration of the ionicdyes proved to be a rather sensitive approach for separating interfacial phenomena from bulk responses. Thecombination of PMF and electrochemical techniques allows to uncover differences in the specific interfacialinteractions of tris(2,2‘-bipyridyl)ruthenium(II) (Ru(bpy)32+), meso-tetrakis(N-methylpyridyl)porphyrinato zinc(II) (ZnTMPyP4+), and meso-tetrakis(p-sulfonatophenyl)porphyrinato zinc(II) (ZnTPPS4-). While Ru(bpy)32+shows quasi-reversible ion transfer features, the charged zinc porphyrins exhibit adsorption properties at potentialclose to the transfer range. The anionic ZnTPPS4- appears to be adsorbed at the interface at potentials morepositive than the formal transfer potential. On the other hand, the spectroelectrochemical data show thatZnTMPyP4+ is adsorbed at the interface at potentials either side of the formal transfer potential. Due to thedifference in the potential dependence of the adsorption processes, PMF responses associated with interfacialaccumulation from the aqueous side exhibit a different phase shift with respect to adsorption steps from theorganic side. The experimental results clearly demonstrate that adsorption planes at the organic and aqueousside of the interface are physically distinguishable. Furthermore, PMF dependence on the polarization of theexcitation beam allows to estimate average molecular orientation of the adsorbed species.
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