Photochromism of dithienylethenes included in cyclodextrins

The effect of inclusion of diarylethenes in cyclodextrin cavities on cycliz ation quantum yields and on circular dichroism (CD) spectral changes by pho toirradiation was studied. The addition of beta- and gamma-cyclodextrins to an aqueous solution of the open-ring form of 2,2'-dimethyl-3, 3'-(perfluor ocyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (1a) increased th e ratio of the antiparallel conformation. The enrichment of antiparallel co nformation 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 co ncentration of cyclodextrins. The induced CD spectrum of 1 in beta-cyclodex trin reversibly changed from negative to positive by UV irradiation. The sp ectral change was attributed to the change in the direction of transition m oment of 1 in the cavity.