Irie and coworkers have studied DTE derivatives with maleic anhydride (28-29) or maleimide (30-35) rings at the backbone. Compounds 28 and 29 are both photoreactive, with moderate ring-closure quantum yields. Interestingly, the yield of the photo-induced reaction is very sensitive to the solvent polarity (especially 28), with photocyclization yields decreasing with increasing solvent dielectric constant. The authors conclude that in polar media the ring-closure reaction is largely suppressed due to the stabilization of the twisted intramolecular charge transfer state. Our computational results show HOMO and LUMO orbitals with the proper symmetry and localization for photocyclization (Figure ).