Dual fluorescent zwitterionic organogels of a quinoxalinone derivative using cation–anion detection keys

An [18]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 CH 3 COO − ) sensing in CH 3 CN. 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 [18]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 [18]crown-6 site than neutral 1 through effective cation–anion electrostatic interactions. Interestingly, the electrostatically stabilized zwitterionic K + · 1− formed fluorescent organogels in CH 3 CN, 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.