Surface Plasmon Study of Monolayer-Bilayer Transition in Poly-4-BCMU and Poly-3-BCMU Polydiacetylene Langmuir-Blodgett Films

Surface plasmon wave spectroscopy was successfully used to study the monolayer-bilayer transition in poly-4-BCMU and poly-3-BCMU polydiacetylene Langmuir-Blodgett films. The linear refractive index and the thickness were obtained for the monolayer yellow and bilayer red forms of poly-4-BCMU. Surface plasmon coupling using resonance enhancement was found to sufficiently enhance the Raman scattering, so Raman spectra of the monolayer films could be obtained with a relatively small laser intensity of a few milliwatts. The differences in the C═C and C═C vibrational stretching frequencies of the monolayer yellow and the bilayer red films were observed arising from the difference in the effective conjugation for the two forms.