An crown-6 unit was introduced into a cation-anion dual-ion-sensing quinoxalinone derivative (1) as a new fluorescent molecule for successive cation (K+) and anion (F- and CH3COO-) sensing in CH3CN. High anion-sensing abilities for F- and AcO- were observed at the hydrogen-bonded acidic N-H proton of the positively charged K+-capturing 1 at the crown-6 site due to electrostatic cation-anion interactions. On the other hand, the acidic N-H proton of lactam tautomer 1 strongly recognized basic AcO- or F- anions via N-H⋯AcO- or F- hydrogen-bonding interactions, and further AcO- or F- additions facilitated the deprotonation reaction, forming anionic 1-. Anionic 1- showed a much higher K+-sensing ability at the crown-6 site than neutral 1 through effective cation-anion electrostatic interactions. Interestingly, the electrostatically stabilized zwitterionic K+·1- formed fluorescent organogels in CH3CN, acetone, and THF; the organogels underwent reversible transformation between a blue fluorescent organogel and green fluorescent sol by the addition of trifluoroacetic acid (gel → sol) and trimethylamine (sol → gel). Both K+ and AcO- (or F-) ions acted as the key ions in the fluorescent organogel formation.
ASJC Scopus subject areas
- Materials Chemistry