Adsorption Behavior of Charged Zinc Porphyrins at the Water/1,2-Dichloroethane Interface Studied by Potential Modulated Fluorescence Spectroscopy

Abstract

The adsorption properties of ionic fluorescent dyes at the polarized water/1,2-dichloroethane interface were studied by potential modulated fluorescence (PMF) spectroscopy under total internal reflection. Analysis of the frequency-dependent fluorescence associated with modulation of the interfacial concentration of the ionic dyes proved to be a rather sensitive approach for separating interfacial phenomena from bulk responses. The combination of PMF and electrochemical techniques allows to uncover differences in the specific interfacial interactions of tris(2,2‘-bipyridyl)ruthenium(II) (Ru(bpy)3 2+), meso-tetrakis(N-methylpyridyl)porphyrinato zinc(II) (ZnTMPyP4+), and meso-tetrakis(p-sulfonatophenyl)porphyrinato zinc(II) (ZnTPPS4-). While Ru(bpy)3 2+ shows quasi-reversible ion transfer features, the charged zinc porphyrins exhibit adsorption properties at potential close to the transfer range. The anionic ZnTPPS4- appears to be adsorbed at the interface at potentials more positive than the formal transfer potential. On the other hand, the spectroelectrochemical data show that ZnTMPyP4+ is adsorbed at the interface at potentials either side of the formal transfer potential. Due to the difference in the potential dependence of the adsorption processes, PMF responses associated with interfacial accumulation from the aqueous side exhibit a different phase shift with respect to adsorption steps from the organic side. The experimental results clearly demonstrate that adsorption planes at the organic and aqueous side of the interface are physically distinguishable. Furthermore, PMF dependence on the polarization of the excitation beam allows to estimate average molecular orientation of the adsorbed species.

Organization and Reactivity of Nanoparticles at Molecular Interfaces. Part I. Photoelectrochemical Responses Involving TiO2 Nanoparticles Assembled at Polarizable Water|1,2-Dichloroethane Junctions

“…The design of the 0.22-cm 2 cell featuring a piston buret has been described in a previous publication. 39 The electrochemical experiments were performed using a homemade four-electrode potentiostat connected to a PPR1 waveform generator (HI-TEK Instruments). The interfacial capacitance was calculated from admittance measurements using a Stanford Research System SR830 lock-in amplifier.…”

Interfacial behavior of sulforhodamine 101 at the polarized water/1,2-dichloroethane interface studied by spectroelectrochemical techniques

“…The spectroelectrochemical cell used in all of the measurements was analogous to one reported previously [8]. The polarizable water/DCE interface had a geometrical area of 0.50 or 0.22 cm 2 .…”

“…The analysis of electrochemical responses in the presence of surface-active species is complicated due to the primitive understanding of the potential distribution across the interface. Considerable efforts have been devoted to accessing the potential dependence of adsorption by means of spectroscopic techniques such as surface second-harmonic generation [3][4][5][6] and potential-modulated spectroscopy [7][8][9][10]. Potential-modulated fluorescence (PMF) spectroscopy has provided detailed information on the dynamics of charge transfer and adsorption as a function of the Galvani potential difference across the liquid/liquid interface.…”

Determination of the Electrostatic Potential of Oil-in-Water Emulsion Droplets by Combined Use of Two Membrane Potential-Sensitive Dyes

“…On the other hand, we have utilized a spectroelectrochemical method called potential-modulated fluorescence (PMF) spectroscopy 17,18 to study the fluorescence behavior of some different PSDs at the polarized oil (O) | water (W) interface used as a biomembrane model. [19][20][21][22] Then, the potential-dependent fluorescence behavior of the PSDs could be elucidated in terms of relatively slow processes, such as reorientation or adsorption/ desorption reactions at the interface.…”