The mixed LB films of porphyrin-viologen compound (diad) with arachidic acid (AA) are deposited on hydrophobic glass plates successfully. Polarized-UV absorption measurement shows that the angle between porphyrin ring and substrate in mixed LB film is 5.9°. Small angle X-ray diffraction pattern shows 3-grade Bragg diffraction peaks, indicating the mixed LB film has a periodic layered structure. UV-vis absorption spectrum suggests that a J-aggregate of diad is formed in mixed films. SEM results indicate that the uniform "domain" formed by aggregates of diad can disperse evenly in the monolayer of cadmium arachidate by adjusting the surface pressure of mixed monolayer; the size of "domain" becomes larger and the shape becomes uniform with increasing of surface pressure from 2mN/m to 30mN/m, and when surface pressure increases to 40mN/m (corresponding to the collapse pressure of mixed monolayer), the "domain" links and becomes larger "domain" with a variety of shapes. The electronic diffraction pattern also conforms that the phase separation exists in mixed monolayer, the two phases both have the symmetrically ordered hexagonal structures. These results lay the foundation of investigating the relationship between the structure and function of porphyrin diad, and realize to modulate the aggregation of molecules artificially.

Key words: ULTRAVIOLET SPECTROPHOTOMETRY, X-RAY DIFFRACTION ANALYSIS, ELECTRON DIFFRACTION, L-B MEMBRANE, SCANNING ELECTRON MICROSCOPE