Nanostructure and thermal stability of the polyglutamate Langmuir-Blodgettfilms probed by interlayer energy transfer method

Ultrathin films of alpha-helical polyglutamate with long flexible side chai ns (PG) were fabricated by the LB technique, and their nanostructure was in vestigated by the energy transfer method. The rodlike main chain of PG was labeled by incorporating either energy donor (naphthalene, Np) or acceptor (anthracene, An) molecules via short side chains. The fluorescence spectra of Np-An multilayers with the same number of spacing layers gave different energy transfer efficiencies, depending on the mode of depositions. This ph enomenon was interpreted as being caused by the noncentered structure of th e polymer backbone, which was probed by both X-ray reflectometry and fluore scence spectroscopy. The Y-type deposition induced a bilayer structure in w hich the stiff main chains of each monolayer were located close to the cent er of the bilayer. The layered structures showed excellent thermal stabilit y up to around 120 degrees C; By thermal treatment higher than 120 degrees C, the layered structure relaxed to a stable state in which the alpha-helic al backbones in each layer became intermingled.