Intramolecular Electron Density Redistribution upon Hydrogen Bond Formation in the Anion Methyl Orange at the Water/1,2-Dichloroethane Interface Probed by Phase Interference Second Harmonic Generation

Abstract

Surface second harmonic generation (SSHG) studies of the azobenzene derivative p-dimethylaminoazobenzene sulfonate, often referred as Methyl Orange (MO), at the neat water/1,2-dichloroethane (DCE) interface is reported. The two forms of the anionic MO dye, which are usually observed in bulk solution, with one form being hydrogen bonded to a water molecule through the azo nitrogens (MO/H2O) and the other form not being hydrogen bonded (MO) have also been observed at the water/DCE interface. Their equilibrium constant has been compared with the corresponding bulk solution and found to be identical. The adsorption equilibrium of the two forms has been determined and the Gibbs energy of adsorption measured to be -30 kJmol(-1) for both forms. From a light polarisation analysis of the SH signal, the angle of orientation of the MO transition dipole moment was found to be 34 +/- 2 degrees for MO and 43 +/- 2 degrees for MO/H2O under the assumption of a Dirac delta function for the angle distribution, a difference explained by the different solvation properties of the two forms. Furthermore, the wavelength dependence analysis of these data revealed an interference pattern resulting from the electronic density redistribution within the hydrated anionic form occurring upon the formation of the hydrogen bond with a water molecule. This interference pattern was clearly evidenced with the use of another dye at the interface in order to define a phase reference to both forms of Methyl Orange.

The Effect of Polar Head and Chain Length on the Physicochemical Properties of Micellization and Adsorption of Amino Alcohol‐Based Surfactants

“…The concentration of OM retained to conduct this work is 50 μmol L −1 that gives the suitable absorbance value (Alehyen et al, 2010). The band at 465 nm corresponds to the solution of OM in the absence of surfactants according to Rinuy et al (2000), this band is attributed to the π π* transition of the hydrated form of OM. On the other hand, Giri et al (2012) assign the same band to a n !…”

Ultrafast Population Dynamics of Surface-Active Dyes during Electrochemically Controlled Ion Transfer across a Liquid|Liquid Interface

“…Therefore, the trans conformation was assumed to dominate the nonlinear response due to a larger first hyperpolarizability. Considering that the transition dipole moment of the trans configuration is essentially oriented along the main molecular axis, we also assumed that in the absence ofthe pump beam the angle of orientation of the transition moment of MO with respect to the interface is similar to that estimated by Rinuy et al, 27 In order to study the dynamics of MO during the ion transfer across the interface, an external electrical field was applied across the interface by using a four-electrode cell described in the Experimental Section with the chemical composition illustrated in Scheme 2. Figure 3 displays the voltammetric response associated with the transfer of MO from the aqueous to the organic phase.…”

Influence of Host's Substitution on the Orientation of the Guest: Pseudo-rotaxanes of Charged Cyclodextrins with Methyl Orange in Solution

“…In the present work, a non-symmetrically end-disubstituted conjugated molecule, methyl orange (MO), is studied as the insert in natural CD cavities (Scheme 1) as well as in synthetically modified CDs bearing either anionic or cationic groups on their primary (narrow) side. The guest molecule has the additional characteristic of possessing an overall dipole moment along its extended axis [7]. Our point of interest was to investigate whether the charge on the host can dictate the orientation of MO inside the cavity.…”