Nitronyl nitroxide and imino nitroxide mono- and biradicals in Langmuir and Langmuir-Blodgett films

In an effort to prepare high-spin-ordered layers, several conjugated molecu les bearing one nitronyl nitroxide radical (NN) or two imino nitroxide magn etically coupled radicals (IN) have been synthesized. The monoradical and t he biradical molecules proved to be amphiphilic enough to form Langmuir fil ms on a water surface. For the two monoradicals, the molecular area extrapo lated at zero-surface pressure in the final part of the isotherms is nearly the same (A(0) similar to 0.55 nm(2) molecule(-1)) and close to what may b e expected for such molecular shapes. For the longest rigid-rod biradical, bis imino nitroxide pentamer, 5p(bisIN), the pressure-area isotherm shows a low compressibility and Brewster angle microscopy has revealed that the fi lm is solidlike, the molecules having a tendency to aggregate, forming plat es on the water surface. The bis imino nitroxide trimer, 3p(bisIN), has a l arger final molecular area A(0) similar to 0.80 nm(2) molecule(-1), the mol ecules being, by then, oriented perpendicular to the surface as deduced fro m grazing incidence X-ray analysis (GMA) and surface potential measurements . After deposition of monolayers on various hydrophilic substrates by the L angmuir-Blodgett (LB) technique, the biradical 3p(bisIN) happens to be the most interesting molecule since good transfer ratios (TR) are easily obtain ed and electron paramagnetic resonance (EPR) measurements indicate paramagn etic properties. In addition, atomic-force microscopy (AFM) imaging of the films shows defects in the form of elevated zones. The AFM reveals that the se zones are partially made of molecules piling up, their heights being mul tiples of single-molecule lengths. These elevated domains occur in differen t shapes, either randomly distributed circular zones or aligned, coalesced domains lying along preferred directions. Y-type multilayers up to nine lay ers were also transferred on hydrophilic glass, with a somewhat poorer TR.