Photochromism of Fulgenates Possessing Crown-Ether Moiety

Molecular switches as photocontrollable “smart” receptors

“…The photochromism of three fulgenates bridged with tri-(5a), tetra-(6a), and pentaethyleneglycoles (7a) as binding sites and the interactions with Li + , Na + and K + of their colourless and coloured forms were reported. 23 Compound 5a and its closed isomer 5b did not bind cations effectively because of the small size of their ionophore. The association constant for Na + was large for 6a and that for K + was large for 7a.…”

“…83 Binding of alkali metal ions such as Li + , Na + , and K + by their crown rings leads to isomerization of spirobenzopyrans in the dark. NMR spectroscopy carried out on complexes containing the NMR active isotopes 7 Li and 23 Na suggested that cations, most significantly Li + , coordinated by the crown moiety in the merocyanine isomer are subject to intramolecular interactions with the merocyanine phenoxide anion. The additional-binding-site effect is eliminated on exposure to visible light as the cation-bound merocyanine readily reverts to its closed form, releasing the metal ions to some extent.…”

“…23 Compound 5a and its closed isomer 5b did not bind cations effectively because of the small size of their ionophore. The association constant for Na + was large for 6a and that for K + was large for 7a.…”