pH-stimulus response dye-cucurbituril sensor for amino acids in aqueous solution

The host-guest inclusion complexes that comprise an inverted cucurbit[7]uril (iQ[7]) and a quinoline derivative, 4-(4-dimethylaminostyryl) quinoline (DSQ) at different pHs were exploited as multiple supramolecular sensors to sense l-α-amino acids. DSQ complexation inside iQ[7] at different pHs leads to increased fluorescence and formation of different-colored iQ[7]-DSQ complexes. The enhanced fluorescence of DSQ after iQ[7] encapsulation may be attributed to limited dimethylamine rotation and the formation of a twisted internal charge transfer (TICT) state. The DSQ@iQ[7] sensors have different affinities for l-α-amino acids at different pHs. Therefore, we propose a pH-stimulus response supramolecular sensor for the discrimination of structurally similar l-α-amino acids in aqueous solution.