Photochromism of spiropyran in molecular sieve voids: effects of host-guest interaction on isomer status, switching stability and reversibility

Spiropyran or its preferred configurational isomers, respectively, are inco rporated in faujasite (NaY, HY and DAY) cages by in situ synthesis, and in Si-MCM-41 channels by wetness impregnation. Luminescence spectra of the col ored isomers indicate the non-aggregated incorporation of merocyanine forms . High quantum yields for the photochromism (similar to 75%) demonstrate th e ready access of the chromophores for the photons of the laser pulses, use d for the photoinduced switching between the different configurational isom ers. The strong retardation of the thermal relaxation rate from the photopr oduct cis-merocyanine to the thermodynamically preferred trans-merocyanine in the faujasite hosts (HY, DAY) in comparison to spiropyrans in SiO2 or Al 2O3 is attributed to an increase of the rotation barriers by the imposed sp atial restrictions. Among the different faujasites the dealuminated Y-zeoli te (DAY) exhibits the lowest relaxation rates of the photoproduct and the h ighest switching reversibilities between the trans- and the cis-merocyanine .