Chemical Physics and Dynamics of Surfaces – Soft interfaces and thin films – Polymerizing 2D Diacetylenes Film

Significant research activities are currently devoted to the development of biological and chemical sensors using molecular films made of diacetylene (DA) molecules which general formula is R-C≡C-C≡C-R’ where C≡C-C≡C is the diacetylene moiety and R and R’ are substituent groups. These materials can polymerize under irradiation in a topochemical way forming, usually, a blue polymer that can turn red under various stimuli (pH, temperature, solvent…). They are then potential candidates for sensing applications. Then, increasing efforts have been made to design various sensing systems with polydiacetylene based materials, mainly on the synthesis of specific target-receptor couples derived from 10,12 pentacosadiynoic acid (PCDA). However, monolayer appears as more appropriate than bulk crystal to improve the signal/noise ratio when probing color changes. Considering this point, the Langmuir film procedure, appears as an adapted study base since one can easily adjust the physico-chemical parameters (temperature, surface pressure). We aim in understanding the color transition. However, we observed that the structural behavior of these films can be strongly affected by the presence of the interaction between diacetylene group. Indeed, we observed an unusual transition from an ordered phase to a disordered one when compressing a Langmuir monolayer of CH₃(CH₂)₁₂-C≡C-C≡C-(CH₂)₃-CH₂OH amphiphilic molecules.