ORIENTATION CONTROL OF FUNCTIONAL MOLECULES IN LANGMUIR-BLODGETT-FILMS USING A TRIGGER MOLECULE - THE EFFECT OF SUBSTITUTION OF THE FUNCTIONAL MOLECULE

This paper reports the effect of the substitution of porphyrin molecule on its orientation change in a Langmuir-Blodgett (LB) film using a long-chain n-alkane, hexatriacontane. Electron spin resonance spectra and polarized UV/vis absorption spectra of the LB films containing derivatives with -S(C6H5), -SO(C6H5), -OH and -NHCOCH3 groups suggest that the orientation as well as the aggregation of these derivatives in the LB film can be changed by the introduction of hexatriacontane as a trigger molecule, in a similar manner to that observed for the unsubstituted porphyrin. The macrocycle plane of these derivatives tilts with respect to the surface normal of the LB film without hexatriacontane, whereas the macrocycle is almost perpendicular to the film surface in the presence of hexatriacontane. In contrast, the orientation of the derivative with carboxylic acid, -NHCO(CH2)2COOH, was not affected by the presence of hexatriacontane. Furthermore, in-plane anisotropy was observed in the UV/vis and ESR spectra for the LB films of this derivative, and was not observed in those for the unsubstituted porphyrin or the other derivatives.