Reversible Change in Optical Properties of Chromophores in Zeolites by Interaction with Alkali Metal Cations

Reversible color changes of chromophores in cationic zeolites were investigated in order to elucidate the effect of cations and chromophores on the color change. We prepared a series of alkali metal cation exchanged zeolite Y and mordenite accommodating N,N -dimethyl- p -nitroaniline (DMpNA) molecules. The UV−vis absorption spectra showed an extraordinarily large red shift of the π−π* bands of DMpNA in the dehydrated form. The degree of the red shift is larger as the size of the cation decreases. 13 C MAS NMR spectra showed sites and dynamic behavior of DMpNA. The color change behavior was also examined for p -nitroaniline and N -methyl- p -nitroaniline in NaY. Large red shifts of the π−π* bands were again observed in the dehydrated form, and the degree of the band shift was correlated well with the scale of susceptibility of the chromophores to the solvent polarity. These results indicated that the color change behavior depended on the combination of cationic zeolites and guest chromophores.