Photochromism of spirobenzopyran in the membrane of surfactant vesicle and in the cavity of cyclodextrins

Abstract

Photochromic reaction of water insoluble 1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-indoline] (SP) was studied in water with the aid of vesicles and γ-cyclodextrin (γ-CD). In both systems, the photochromic reaction of SP was observable in spite of the low solubility of SP in water. In order to examine the microenvironment around the SP and the reaction product, photomerocyanin (MC), in those systems, the spectrum of MC was measured in various organic solvent of various polarity. Decreasing the polarity of the solvent decreased the peak absorbance and shifted the peak wavelength to the long wavelengths. When the vesicles were used, the reactant, SP, and the product, MC, were solubilized in different regions of different polarity. The reaction substrate was then supposed to have moved from the hydrophobic region of the membrane to the hydrophilic one after the photoisomerzation. The photochromic reaction of SP in the presence of γ-CD was slower than in the vesicles and faster than that in methanol. The polarity in the vesicular membrane and the limited rotation of the reactant in the cavity of γ-CD may have influenced the reaction rate. The prolonged light irradiation period resulted in a simultaneous photoreaction and polymerization, producing some unknown side reaction.