A new highly selective calix[4]crown-6 fluorescent caesium probe

We have synthesized 1,3-alternate di-deoxygenated calix[4](9-cyano-10-anthr ylmethyl)benzocrown-6, 1 and 1,3-alternate calix[4](9-cyano-10-anthrylmethy l)benzocrown-6, 2 as the second generation of caesium selective fluorescent probes; probe 1 shows 54-fold fluorescence enhancement upon caesium comple xation while 2 exhibits only 8-fold enhancement; the selectivity ratios for 1 to complex caesium ion over potassium and rubidium (K-Cs/K-K and K-Cs/K- Rb) are ca. 10 fold higher than those of 2 for the same ions; the observed selectivity ratios are consistent with data reported for other 1,3-alternat e calix[4]crown-6 derivatives.