The photochromic behavior of spiropyran molecules is very sensitive to the property of surrounding media. Enhanced isomerization of spiropyran to merocyanine was observed after storing functionalized zeolites under ambient temperature and moisture for an extended period of time. Experimental results based on infrared spectroscopy suggest that the enhanced isomerization is due to an increase in the amount of surface-adsorbed water. The presence of more surface-adsorbed water likely altered the isomerization by stabilizing the merocyanine isomer. This observation was utilized to improve reversibility of the isomerization between spiropyran and merocyanine on NaY zeolite surfaces for potential optical applications. (C) 2014 Elsevier B.V. All rights reserved.