Study of Polydiacetylene thin films by Langmuir-Blodgett technique and development of chemical sensors
Polydiacetylenes (PDA) are a class of robust, linear conjugated polymers with alternating triple and double bonds in “yne-ene” motif. Amphiphilic long-chain diacetylene monomers, compressed at the air-water interface and then UV polymerized form an ultra-thin, stable trilayer structured Langmuir film (LF). Irradiation with UV light leads to their topotactic photopolymerization forming initially the metastable blue phase and for further irradiation, transition to a stable red phase takes place . The blue and red phases of the PDA are characterized by the absorption maxima at ca. 640 nm and ca. 550 nm respectively. PDA, due to its conjugated backbone, has a characteristic absorption in the visible and an efficient emmitance in the red . PDA multilayer can be prepared using sequential deposition in Langmuir-Blodgett (LB) method or by ultrasound agitation of aqueous solutions to form vesicles. This organization pins the polymer chains in a 2-dimensional crystal structure and further enhances the conjugation and hence the polymer chromic behaviour.