Fluorescent chemo-sensor for metal cations based on thiacalix[4]arenes modified with dansyl moieties at the lower rim

The selective de-tert-butylation of p-tert-butyl thiacalix[4]arene (p-tert- butyl TCA) with AlCl3 at 80 degrees C has been investigated. Mono-, di-, an d tri-p-tert-butyl thiacalix[4]arene (mono-, di- and tri-TCA, respectively) were obtained in yields of 6.5, 20 and 21%, respectively, when p-tert-buty l TCA was treated with 7.1 equiv. of AlCl3 for 30 min. De-tert-butyl TCA (T CA) was exclusively obtained when 10.5 equiv. of AlCl3 was used. These deri vatives are converted to fluorescent active derivatives by modification wit h dansyl moiety at the lower rim, which are used as metal sensors in aqueou s solution. The extent of the fluorescent variations with the metal cations was used to display the sensing factors, Delta I/I-0. These hosts show muc h higher sensitivity for transition metal cations such as Co2+, Ni2+, and C d2+ than those of alkali metal cations such as Li+, Na+, and K+. The effect of p-tert-butyl groups on metal sensing ability of these hosts was studied . It was found that p-tert-butyl, groups decrease the sensing ability of th ese hosts. It is the first example to show that water soluble TCA derivativ es can detect metal cations directly in aqueous solution by variation of fl uorescence intensity upon addition of a metal cation. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.