Controlled Phase Separation in Poly( p-phenyleneethynylene) Thin Films and its Relationship to Vapor Sensing Properties.

In this paper, we report the synthesis and mesoporous film formation of hydrophobic rod-like poly( p-phenyleneethynylene)s (PPEs) and present porosity-dependent quenching studies using 1,3,5-trinitrotoluene (TNT) vapors. Non-solvent vapor-induced phase separation (NVIPS) was used to induce pore formation during film casting, and the concentration of PPEs in the casting solution was controlled carefully to prevent excimer formation. We found that the structure of the sidechains of the PPEs strongly influence the range of the relative humidity at which controlled pore generation occurs, which could be rationalized from interfacial energies calculated from contact angle measurements. Porosity of the PPE films resulted in increased efficiency of fluorescence quenching towards TNT vapor, which previously required very thin films (below 5 nm) for sensing applications. The control of the porous structure as well as film thickness constitutes a promising strategy for enhancing the efficiency of chemosensor and in more general applications requiring fine-tuned polymer-gas interactions.