Volume-demanding cis-trans isomerization of 1,2-diaryl olefins in the solid state.

Volume-demanding cis-trans photoisomerization of the aromatic substituted alkenes 1-3 in the solid state at room temperature and at 50 degrees C is presented. Alkene 3 did not undergo the cis-trans isomerization in the solid state either at room temperature or at 50 degrees C. The importance of the presence of void space near the reaction center to facilitate the large volume change during cis-trans photoisomerization is discussed.