PHOTOCHEMICAL CLOSING AND OPENING OF THE GUEST-BINDING CAVITY OF CYCLODEXTRINS

CYCLODEXTRINS and modified derivatives can bind, and sometimes modifg the properties of, guest molecules in their torus-shaped cavities(1,2) . They have also been used as the building blocks of molecular materia ls and devices(3). The propensity to bind and retain a guest is not ea sily predictable or controllable, however. There is currently much int erest in the switching on and off of chemical(4) and biological(5) act ivity, particularly by photochemical means(6), as such functions will be required of molecular-scale devices. Here me report the controlled binding and release of guest molecules in cyclodextrins modified with substituents that can reversibly form bridging units across the cavity openings. Irradiation of percinnamoylated alpha- or beta-cyclodextrin in N-methylpyrrolidin-2-one (NMP) leads to the formation of intramole cular cyclobutane bridges which trap a bound NMP molecule. Irradiation at a different wavelength breaks open the cyclobutane rings and relea ses the guest.