Synthesis of novel p-tert-butyl-calix[4]arene derivatives and their cation binding ability: chromogenic effect upon side arms binding

A series of novel double-armed calix4]arene derivatives, i.e. 5,11,17,23-tetra-tert-butyl -25,27-bis2-(2-hydroxy-5-(4-nitroazo)benzylidene)amino]ethoxy]-26,28-dihydroxy-calix4]-arene (4), 5,11,17,23-tetra-tert-butyl-25,27-bis2-(2-hydroxy-5-(2-nitroazo)benzylidene) amino]ethoxy]-26,28-dihydroxycalix4]arene (5), 5,11,17,23-tetra-tert-butyl-25,27-bis2-(2-hydroxy-5-(4-chloroazo)benzylidene)amino]ethoxy]-26,28-dihydroxycalix4]arene (6), have been synthesized as an selective chromoionophore for Na⁺. The complexation behavior of ligands 4-6 with alkali metal ions Na⁺, K⁺, Rb⁺and Cs⁺ has been evaluated by using UV-Vis spectrometry in CH₃CN-H₂O (99:1/V:V) solution at 25°C. The UV-Vis spectra show that the complexation of 4-6 with Na⁺exhibits obvious bathochromic shifts (λ_max 379→480 nm) and there is a unique color change in the solution from yellow to red upon complexation. The binding constants for Na⁺ are higher than that of other alkali metal ions, giving the highest cation selectivity up to 7 for Na⁺/K⁺. The binding ability and photophysical behavior of alkali cations by calix4]arene derivatives 4-6 are discussed from the point of view of substituted effects at the lower rim of parent calix4]arene and size-fit concept between host calix4]arenes and guest cations.