Volume-Demanding Cis<i>−</i>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 °C is presented. Alkene 3 did not undergo the cis−trans isomerization in the solid state either at room temperature or at 50 °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.