Influence of molecular structures of europium bisphthalocyanines on organization of supramolecular assemblies formed at the air/water interface

The monolayers at the air/water interface, the Langmuir-Blodgett (LB) monolayers and multilayers on solid substrates of five kinds of europium bisphthalocyanines EuPc2 (Eu1), EuPc[Pc(OC5H11)8)] (Eu2), EuPc[Pc(C7H15)8] (Eu3), Eu[Pc(OC5H11)8)]2 (Eu4) and Eu[Pc(C7H15)8]2 (Eu5) were characterized by using π-A isotherms, UV-vis spectra, polarized UV-vis spectra, low-angle X-ray diffraction (LAXD) and transmission electron microscopy (TEM). The results demonstrate that the different molecular structures have great influence on the orientation of the macrocycles, on the configuration of the molecules and on the organization of the supramolecular assemblies at the air/water interface. In the aggregates of Eu1 molecules, the macrocycles stack closely in a face-to-face mode with an orientation angle of 51 deg. . Eu2 and Eu4 form homogeneous monolayers at a lower surface pressure due to the stronger hydrophilicity of the substituents, in which the molecules take the face-on configuration with the Pc rings in contact with the water surface. The orientation angles are ca. 45 deg. and 30 deg. , respectively, and the chains extend to the air. Eu5 molecules take an edge-on configuration with the ring orientation angle of ca. 30 deg. at the air/water interface form rod-like supramolecular structures. Eu3 does not form an ordered structure at the air/water interface due to the asymmetric molecular structure