We also explored the kinetics of the thermal ringopening of dihydro-4H-cyclobuta [c]isochromenes to recover 1H-2-benzo [c]oxocins (Figure and Table ). The kinetic experiments clearly show that the ring-opening process is a first-order reaction (see SI for details) and the reaction rate is essentially solvent independent (Figure ). The isomer yield going from closed-to open-form ranges from 62-70% in these cases, with no obvious substituent influence (Table ). Since the dihydro-4Hcyclobuta [c]isochromenes are stable at room temperature and no obvious reversible ring-opening products could be observed under ambient conditions, the half-life time (t1/2) of the ring-closed isomers could be extrapolated from kinetic measurements across the temperature range 90-130°C using the Eyring equation (SI for details). For the dihydro-4H-cyclobuta [c]isochromenes mentioned in Figure and Table , the t1/2 ranges from 44-67 years, demonstrating the considerable stability of the metastable isomers during application as photoswitchable materials.