Photo-induced trans-cis isomerization and orientation of cyano-substituted 4'-N,N-dimethylamino-nitrosilbene (DANS) and phenylhydrazone derivatives doped polymer films have been studied. Comparing with DANS, these molecules show large photoinduced optical anisotropy (POA) due to the addition of cyano-group onto C=C or C=N bond which makes these molecules be much more easily photoisomerized. The mechanism of POA can be understood well by the current theories. Qualitative and quantitative explanations were given based on the trans-cis quantum yield, absorption spectrum, cis-trans relaxation, interaction with the host polymer, and the molecular structure. (c) 2005 Elsevier B.V. All rights reserved.