Analysis of gibbs monolayer adsorbed at the toluene/water interface by UV-visible partial internal reflection spectrometry

Gibbs monolayers of lipophilic tetraphenylporphyrinatomanganese(III) and hydrophilic diacid of meso-tetrakis(4-sulfonatopheny)porphyrin adsorbed at the liquid−liquid interface have been analyzed by UV−visible external reflection (ER) and partial internal reflection (PIR) spectra measured at different angles of incidence. The angle-dependent ER and PIR spectra over the Brewster angles ( and ) have readily been measured at the toluene/water interface. As preliminarily expected in our previous study, the present study has first proved that the reflection−absorbance of UV−visible PIR spectra quantitatively agrees with the theoretical calculations for the Gibbs monolayer over . In addition, it has also been proved that the absorbance of the PIR spectra is greatly enhanced in comparison to that of the ATR spectra. The enhancement is caused by an optical effect in the monolayer sandwiched between two phases of toluene and water that have different but refractive indices close to each other. This optical enhancem...