Monolayer and Langmuir-Blodgett Multilayer Surface and Spectral Studies of Poly-3-BCMU

Monolayer films of poly-3-BCMU are shown to form at the air-water interface, the surface pressure/area per residue (π/A) isotherms of which exhibit a horizontal plateau indicative of a phase change occurring on compression. Langmuir-Blodgett monolayer films, transferred while proceeding through this region, have visible absorption spectra indicating a conformational change from an amphipathic yellow to a nonamphipathic blue form having increased π-electron conjugation. A thermodynamic analysis of the temperature dependency of the compressions onset of the plateau (π_t), interpreted in terms of a corrected two-dimensional analogue of the Clapeyron equation, shows a slightly exothermic transition. A comparison of isotherms obtained both by continuous compression and by a stepwise “equilibrium” method shows considerable relaxation can take place at areas per residue less than 100 Å2. This is interpreted as reflecting the pronounced reorganization required for the highly ordered blue conformation to completely form. Multilayers of poly-3-BCMU and poly-4-BCMU transferred at different areas per residue show visible absorption spectra reflecting the different degrees of conformational order of the monolayer films from which they were fabrica ed. When monolayers of poly-4-BCMU and poly-3-BCMU are sandwiched, an alternating multilayer is formed in which the highly ordered blue conformation is forced to assume the slightly less ordered red conformation of poly-4-BCMU.