Potential-Dependent Adsorption and Orientation of meso-Substituted Porphyrins at Liquid|Liquid Interfaces Studied by Polarization-Modulation Total Internal Reflection Fluorescence Spectroscopy

Abstract

Potential-dependent adsorption behavior of meso-substituted water-soluble porphyrins at the polarized water|1,2-dichloroethane (DCE) interface was studied by polarization-modulation total internal reflection fluorescence (PM-TIRF) spectroscopy. In the PM-TIRF experiments, the fluorescence signal from the interfacial region was analyzed as a function of the periodic modulation of linear-polarizations (p and s) of the incident excitation beam. The potential-dependence of PM-TIRF responses for meso-substituted porphyrins, 5,10,15,20-tetrakis(N-methylpyridyl)porphyrin (H 2 TMPyP 4+ ) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H 2 TPPS 4− ), indicated that both free base porphyrins were adsorbed with relatively lying orientations at the polarized water|DCE interface. The average orientation angles (θ) were estimated as θ = 61 ± 1°for H 2 TMPyP 4+ and θ = 65 ± 1°for H 2 TPPS 4− with respect to the interface normal. The wavelength-dependence of polarization-modulated fluorescence signals (PM-TIRF spectrum), which corresponds to "pure" emission spectrum of interfacial species, clearly indicated that H 2 TMPyP 4+ and H 2 TPPS 4− are adsorbed with a modification of the solvation at the interface. These results demonstrated a high ability of the PM-TIRF spectroscopy for the direct characterization of fluorescent species adsorbed at polarized liquid|liquid interfaces.

Self-Assembly of Porphyrin Nanostructures at the Interface between Two Immiscible Liquids

“…Thus, we avoid acidic conditions (that would lead to the expulsion of the central metal ion), 17 as well as the use of synthetically challenging amphiphilic porphyrin molecules, 18 and more complicated routes using additives (e.g., divalent cations or surfactants) [19][20][21] or external stimuli (e.g., electric fields). [22][23][24] We chose zinc(II) meso-tetrakis (4-carboxyphenyl)porphyrin (ZnTPPc) as a prototypical model system to demonstrate this new means of self-assembly at an immiscible aqueous|organic interface.…”

A Soft On/Off Switch Based on the Electrochemically Reversible H-J Interconversion of a Floating Porphyrin Membrane

“…The negative values of ΔF p-s at each ∆ o w confirm the relatively horizontal orientation of individual ZnPor molecules within the membrane with respect to the plane of the interface. 23 PM-TIRF spectra measured at -0.06 and -0.15 V show a major decrease in -ΔF p-s compared to the spectrum at +0.29 V, with no spectral shift. The decrease in -ΔF p-s may be associated with a change in molecular orientation of the ZnPor molecules within the membrane at the more negative potentials.…”

A soft on/off switch based on the electrochemically reversible H–J interconversion of a floating porphyrin membrane

“…As demonstrated in previous works, PM-TIRF spectra are interface-specic, with signals arising from randomly oriented molecules in the bulk phases effectively cancelled out. 22,23 At D w o f ¼ +0.59, +0.29, À0.06 and À0.15 V, two emission peaks were observed (l em. ¼ 613 and 663 nm), similar to the emission peaks for the monomeric porphyrin (see Fig.…”