Photochromism of dithienylethenes included in cyclodextrins

The effect of inclusion of diarylethenes in cyclodextrin cavities on cyclization quantum yields and on circular dichroism (CD) spectral changes by photoirradiation was studied. The addition of beta- and gamma-cyclodextrins to an aqueous solution of the open-ring form of 2,2'-dimethyl-3, 3'-(perfluorocyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (1a) increased the ratio of the antiparallel conformation. The enrichment of antiparallel conformation caused an increase in the photocyclization quantum yield of 1a. The CD spectral intensity of the mixtures of 1a or 2,2',4,4'-tetramethyl-3,3'-(perfluorocyclopentene-1,2-diyl)bis(thiophen-5-yl-(phenyl-4-sulfonate)) (2a) and cyclodextrins in aqueous solution increased with the increasing concentration of cyclodextrins. The induced CD spectrum of 1 in beta-cyclodextrin reversibly changed from negative to positive by UV irradiation. The spectral change was attributed to the change in the direction of transition moment of 1 in the cavity.