The investigation of switching cycles and fatigue resistance were also performed in our novel switching system. All the switching molecules mentioned in Table and Figure demonstrate good performance in switching cycles, with several rounds of conversions between dihydro-4H-cyclobuta [c]isochromenes and 1H-2benzo [c]oxocins easily achieved by switching between light and heat (more details of repeated switching cycles are shown in SI). The fatigue resistance of the series reveals a substituent dependence, with compound 12b (containing a -CF3 electron-withdrawing group) exhibiting the best fatigue resistance among these five groups of photoswitches, with to only ~2% dihydronaphthalene formation per switching cycle, formed during the thermal ring-open process at 110C (see SI for details).