Photopolymerization of diacetylene Langmuir-Blodgett films on an azobenzene-containing monolayer

Single layered Langmuir-Blodgett (LB) films of 10,12-pentacosadiyonic acid (PDA) were prepared on a monolayer comprised of an azobenzene (Az) containing polymeric amphiphile. The photopolymerization process of this PDA LB film on ultraviolet (UV) light (254 nm) irradiation was followed by UV-Vis absorption spectroscopy. The conjugation state of the resulting polydiacetylene was dependent on the initial isomerization form of the Az monolayer beneath the diacetylene LB film. The trans- and cis-Az surfaces led to a blue and red colored polydiacetylene film, respectively. Atomic force microscopic observation revealed that the photopolymerization of PDA enlarges the surface roughness within the molecular length of the amphiphiles, indicating that the molecular layer structure is preserved on polymerization. The polymerization behavior in this system was highly sensitive to humidity. This can probably be correlated to an enhanced molecular mobility of 6Az10-poly(vinyl alcohol) (PVA) monolayer in a humid atmosphere.