Structural Effect of Amphiphilic Crown Ether Azoprobes on Alkali Metal Ion Recognition and Aggregation Behavior in Water

Amphiphilic azoprobes having a crown ether moiety (15C5–Azo–Cn; n=4, 6, 8, and 12 and 18C6–Azo–Cn; n=4, 6, and 8) were synthesized. We examined the effect of alkyl spacer length of the amphiphilic azoprobes on the spectral response to alkali metal ions in water by UV–vis spectral and 1H NMR measurements. 15C5–Azo–Cn exhibited self-assembly in response to K+ selectively and the most selective response to K+ was observed for an azoprobe possessing a hexyl spacer unit (15C5–Azo–C6). 15C5–Azo–C12 formed nano-size aggregates. 18C6–Azo–Cn (n=6 and 8) showed Cs+ selectivity and its molecular aggregation behavior was similar to that of 15C5–Azo–Cn.