Studies on the Composite Langmuir−Blodgett Films of Tetracationic Porphyrazine Cobalt and Methyl Orange

By spreading the amphiphilic cobalt tetrahexadecyl-tetrapyridinoporphyrazinium bromide (TA 16 PyPzCo) on the air/aqueous methyl orange (MO) solution interface, composite monolayer of TA 16 PyPzCo/MO was formed. Composite Langmuir−Blodgett (LB) films have been fabricated and characterized by means of UV−vis spectra, IR spectra, and X-ray diffraction (XD). The molecular orientation was estimated by using polarized UV−vis and polarized IR absorption measurements. The orientation angles of the hydrocarbon chains of TA 16 PyPzCo, the macrocycle, and the MO with respect to the normal of the substrate were estimated to be 49.5°, 56.9°, and 46.2°, respectively. The XD patterns of the LB films showed a well-defined lamella structure, and the d value was 6.04 nm. Based on these results, a possible film structure was proposed, in which the MO unit was under the macrocycle in the composite monolayer, and the long alkyl chains were interpenetrated in the adjacent TA 16 PyPzCo layer in the LB films. The trans to cis photoisomerization of the azobenzene group in MO molecules in LB films has been investigated.