Ellipsometric studies of photochromic ultra thin polymer films

We present ellipsometric measurements on Langmuir-Blodgett (LB) monolayer assemblies of photochromic polymers; the polymer we used was a statistical copolymer with polymethacrylate mainchains and azobenzene sidegroups. Ellipsometry gives a value of n 1.557 for the refractive index and a film thickness of 1.58 nm per monolayer, When exposed to light of appropriate wavelength, the azobenzene groups undergo a trans <-> cis photoisomerisation process which was monitored by ellipsometry. We found an average change in film thickness of 0.02 nm per monolayer during the trans<->cis transition process, whereas the data obtained do not show any significant change in refractive index.