Emptying the β-cyclodextrin cavity by light: photochemical removal of the trans-chalcone of 4',7-dihydroxyflavylium.

The interaction between the network of chemical reactions of the compound 4',7-dihydroxyflavylium and β-cyclodextrin was studied by means of pH jumps, followed by UV-vis absorption, flash photolysis, stopped flow, and NMR. The trans-chalcone is the network species exhibiting the strongest interaction with the host. In moderately acidic medium, 95% of the trans-chalcone, 2.5 × 10(-5) M, in the presence of β-cyclodextrin, 9 × 10(-3) M, is expected to fill the host cavity (association constant 2.2 × 10(3) M(-1)). In contrast, flavylium cation does not interact (association constant ≈ 0). Irradiation of the trans-chalcone in the presence of β-cyclodextrin 9 mM leads to the flavylium cation appearance. Light is thus capable of removing the trans-chalcone from the β-cyclodextrin, leaving the cavity empty. The system is reversible and trans-chalcone goes back to the initial state upon switching off the light due to the thermodynamic favorable conversion of flavylium cation to trans-chalcone in the presence of β-cyclodextrin.