Polymer conversion measurement of diacetylene-containing thin films and monolayers using soft X-ray fluorescence spectroscopy

Polymer formation within ordered monolayer and thin-film assemblies is measured using fluorescence yield near-edge spectroscopy (FYNES). This spectroscopic method measures soft X-ray absorption in the 270-330-eV energy range, probing core-electron transitions to unfilled molecular orbitals by detecting the resultant fluorescence emission. By observing transitions in the carbon ls-pi* region (280-286 eV), the diminution of monomer and formation of polymer are measured directly and simultaneously. In contrast with spectroscopic methods measuring partial electron yield, film damage caused by neutralization of sample charging is eliminated with FYNES. Using FYNES, monomer-to-polymer conversion efficiencies for ultrathin films and monolayer assemblies are successfully measured for the first time. Measured conversion efficiencies for diacetylene-containing assemblies is near 80%, demonstrating remarkable agreement among ultrathin films, surface-attached configurations, and previous studies of thicker film structures. Likewise, polymerization kinetics for these assemblies are also similar, exhibiting at least two distinct rate regimes. These results indicate that the polymerization properties of diacetylenes are not significantly dependent on molecular architecture and that induced-dipole interactions between neighboring diacetylenes predominate.