Photoinduced Reversible Optical Gratings in Photochromic Diarylethene-Doped Polymeric Thin Films

We report on our investigation of the potential for all-optical reversible photostructuring of the photochromic molecule 1,2-bis(2-methylbenzo[b]thiophen-3-yl)perfluorocyclopentene (BFCP). The light-induced isomerization of BFCP was studied in solution as well as in polymeric thin films. The absorption change that is due to the photochromic reaction of BFCP was determined by conventional spectroscopic measurements. The absolute values of the refractive indices of doped polymer films were measured by the waveguide grating coupling technique for the two states of the photochromic molecule. The dynamics of the reactions and the light-induced refractive-index changes Δn of doped polymer samples were investigated in holographic grating experiments. Changes of as much as Δn=(3.5±0.5)×10-4 were obtained at 806 nm for 41.16-wt. % doping. Finally, a modified two-beam coupling experiment permitted the separation of absorption and refractive-index contributions to the grating buildup and the determination of the phase shifts of these gratings with respect to the intensity grating.