Polarized light-induced anisotropy of azo dyes studied by polarized FTIR spectroscopy

The anisotropy induced in the poly(methyl methacrylate) (PMMA) films doped with Disperse Orange 3 (DO3, NO2-phenyl-N=N-phenyl-NH2) was investigated by polarized FTIR spectroscopy. Observed infrared absorption bands of DO3 in the polymers were assigned to symmetric (NO2s, 1341 cm−1) and antisymmetric (NO2as, 1523 cm−1) stretching modes of NO2, and the C-N stretching mode of C-NH2 (C-N, 1303 cm−1). By measuring the polarized IR spectra of DO3/PMMA, the infrared dichroism was observed in NO2s and C-N bands. From these results, the orientation factors, KZfn (f=x,y,z), for each isomer were determined. The factors indicate that it is difficult for NO2 group to move in the PMMA during trans-cis-trans isomerization and that phenyl group with NH2 mainly moves in PMMA on isomerization. This study clarified that the anisotropy of DO3 in PMMA is induced by photoselection with the irradiation of linearly polarized light and is not induced by reorientation of DO3 molecules, since the entire DO3 molecule cannot rotate i...