Photochromism of Spiropyran−Cyclodextrin Inclusion Complexes on Au(111)

This paper reports on the switching characteristics of a spiropyran−cyclodextrin inclusion complex on a Au(111) surface. The switching behavior in acetone/water and ethanol/water solution is compared with that of the complex as thin film (∼100 layers) on gold and with the complex in a microcrystalline form. For the inclusion complex, we find a significantly increased switching time from the closed spiro to the open merocyanine conformation as compared to a solution of pure spiropyran. The thin film has a similar switching time as the solution of the inclusion complex. For the microcrystalline form, on the other hand, the switching times are considerably shorter. The back reaction exhibits a switching time for the solution of the inclusion complex which is similar to the pure spiropyran solution whereas the microcrystalline sample switches faster and the thin film of the inclusion complex slower than all the other ones. Furthermore, reversible switching of an adsorbed layer of the complex on gold could be observed. The switching characteristics can be explained in a model considering steric and compressive strain.