Dynamic behavior of photo-induced orientation of poly(methyl methacrylate) – Solvent Red 23 thin films

We investigate the effect of the photo-orientation and stability of the Solvent Red 23 dye incorporated in poly(methyl methacrylate) thin films as a guest–host system. A probe–pump optical system was used to investigate the dichroic behavior of the samples. Orthogonally polarized laser lights induce a smaller increase in the transmitted beam intensity. A stronger polar order was induced using a parallel probe–pump laser light compared to that of the perpendicular state. It was found that the dichroic ratio value of the poly(methyl methacrylate) – Solvent Red 23 thin film increased by 0.174 at the photostationary state, indicating that the net orientation of Solvent Red 23 molecules has increased 17.4% in the direction perpendicular to the applied beam field. The dynamic evolution of the dichroic ratio showed that the relaxation is rather slow, and it deteriorates in a slow exponential fashion, which may take a very long time to reach the isotropic state. The contrast ratios were 0.449 and 0.267 in parallel and orthogonal probe–pump configurations, respectively. The order parameter calculations reveal that about 70% of photo-induced anisotropy remains after relaxation for a long time.