Fig. 2. Reversible transformation between cages 2a and 2b monitored by absorption spectroscopy: (a) formation of cage 2b upon visible light irradiation of cage 2a (40 μM in propylene carbonate containing 1.5 μM methylene blue). (b) Fatigue cycles for the 2a/2b conversion in propylene carbonate in the presence of methylene blue as a photosensitizer. Cycloreversion is conducted by heating to 120 °C for 80–120 min.