Study of Photo-Induced Dichroism in Sudan III Doped in Poly(Methyl Methacrylate) Thin Films

Linear dichroism, dichroic ratio, contrast ratio and order parameters of Sudan III/PMMA guest-host thin films have been investigated with visible polarized laser light. Dichroism increased in an exponential fashion with increase of the pump intensity. Light-induced dichroism and polar order of the dye molecules within the polymer network were reversible. These parameters showed fast increase in their values in an exponential fashion as the pumping process takes place. Also, they decay rapidly in an exponential fashion when the pump light is cut off. Photoisomerisation and polar orientation are dependent on both the molecular structure of the dye and polymer. Two forms of Sudan III molecules (trans and cis) are responsible for the interaction with laser light and forming an anisotropic structure inside the PMMA/Sudan III films. However, there is another set of forms of the dye (keto and enol) has to be considered, which may contribute to dichroism.