PHOTORESPONSIVE BEHAVIOR OF LANGMUIR-BLODGETT-FILMS OF AZOPOLY-L-LYSINE

We report the successful deposition of mono- and multilayers of azopol y-L-lysine (APLL), a synthetic polypeptide to which an azobenzene moie ty has been added as a side chain. Such a molecule in solution shows p hototropism, due to light-induced trans-cis isomerization. The Langmui r-Blodgett (LB) deposition was difficult due to the very high viscosit y of the Langmuir monolayer; we were able however to deposit homogeneo us films up to seven layers. Optical absorption studies showed lineari ty between the optical density and the number of layers. Our main resu lt is that the phototropism of the APLL is preserved in the solid LB f ilm. Under ultraviolet illumination with a 400 W Xe lamp, we found pho toconversion of up to 30% in optical density. Preliminary relaxation m easurements showed a back-relaxation time of the order of 24 h. These results make APLL an interesting system for optoelectronic application s.