Photolysis of 1a yields 4a in argon-saturated methanol, whereas 1b is photostable. Laser flash photolysis of 1a in acetonitrile shows formation of biradical 2a (λmax= 340 nm, τ=∼ 60 ns), which undergoes intersystem crossing to form Z-3a (λmax= 380 nm, τ= 270 ns) and E- 3a (λmax= 380 nm, τ= 300 ms). Z-3a regenerates the starting material, whereas E-3b undergoes intramolecular lactonization to release the alcohol moiety and form 4a. Similar ...
