Design of benzo-15-crown-5 azoprobe/γ-cyclodextrin complexes for alkali metal ion recognition in water

Novel photosignal transduction systems of benzo-15-crown-5 (B15C5) azoprobe/γ-cyclodextrin (γ-CyD) complexes were designed. Four B15C5 azoprobes were synthesized by azo coupling of 4’-aminobenzo-15-crown-5 with phenol (for 15C5-Az-Ph) and N,N-dialkylanilines (for 15C5- Az-Cn). These azoprobes exhibited strong induced circular dichroism (ICD) by forming an inclusion complex with γ-CyD. Examination of the spectral responses and 1H NMR analysis of the B15C5 azoprobe/γ-CyD complexes in the presence of alkali metal cations revealed that K + binding selectively induced dimer formation of the B15C5 azoprobes inside the γ-CyD cavity, which resulted in distinct changes in their UV-vis and ICD spectra in water. The effect of alkyl chain length of 15C5-Az-Cn n    γ-CyD complexes was examined in 90% H2O/10% CH3CN (v/v). The highest K+ ion response was noted for the 15C5-Az-C2γ-CyD complex. The 15C5-Az-C4γ-CyD complex was found to show abnormally high ICD responses for TMA+ and Cs+.