In-Situ Measurements and Molecular Orientation by External Reflection Spectrometry of Liquid-Liquid Interfacial Adsorbates of Porphyrins.

点击翻译按钮获取中文摘要

The authors investigated the interfacial adsorption states of lipophilic-porphyrins (H_2P) in a protonated form (H_4PX_2) at the inert organic solvent/aqueous inorganic acid (HX) solution interface by development of in situ measurement devices for partial reflection spectrometry, including external reflection (ER) and partial internal reflection (PIR).1.Stoichiometric analysis of protonated tetraphenylporphyrin in an aggregate (H_4PX_2)_<n,i> was accomplished using a simple device comprising a liquid cell and prisms. (1)In the toluene-4 M H_2SO_4 system, ER spectrometry was effective to distinguish interfacial adsorbates from lipophilic solute in the organic phase (H_2P)_o. (2)In the dodecane-4 M H_2SO_4 system, all (H_2P)_o was protonated to yield (H_4PX_2)_<n,i> and aqueous species, H_4P^<2+>_<aq>. The relationship of reflection absorbance at each of bands for interfacial molecular density [H_4PX_2]_i suggested that the interfacial adsorption state changed from a monolayer form to a … More multilayer one with a different reflection coefficient. (3)The saturated interfacial molecular density in the dodecane-4 M H_2SO_4 system was estimated to be 1.20×10^<-10> mol cm^<-2> ; it yields a tilt angle 47°of pyrrole ring plane against the interface normal.2.No aggregation was found in the lipophilic tetraphenylporphyrin derivatives with substituent at ortho-position in meso-phenyl group. Whereas, protonated tetra-p-torylporphyrin could associate to form some aggregate. These suggest the molecular association is depend on the rotation nature of phenyl-group to yield a planar-type molecular structure.3.The incident angle dependence of reflection spectra was studied using a home-made variable-angle device. Positive and negative bands have been observed in the p-polarized PIR spectra, whose band location correspond to those in p-polarized ER spectra. Nevertheless, the bands in the p-PIR exhibited reversed sign to those of p-ER spectra. These suggest that the interface selection rule of the p-PIR spectrometry has a reversal rule of p-ER, and PIR can also be used for the analysis of molecular orientation. Less