Host–guest assembly of H33258 dye in cucurbit[7]uril and specific recognition for HPO42− anion

In the present work, a well-known host–guest inclusion complex comprising a cucurbit[7]uril (Q[7]) and an important biological dye, Hoechst-33258 (H33258) was selected as a fluorescence probe. In contrast to the pH conditions in which H33258 is exhibited in the literature, these being, mono- or di-protonated states, in the present work, we selected an extreme case, whereby H33258 was displayed in an anionic state (pH = 11). The investigation of the host–guest interaction demonstrated similar inclusion modes in a wide pH range, that is the dumbbell-like inclusion complex in which one Q[7] includes piperazine moiety and another Q[7] includes the phenol moiety of H33258. Moreover, investigation on the binding capacity of the 15 selected anions under three representative pH levels (pH = 2, pH = 4.5 and pH = 11, respectively) indicated that the H33258@Q[7] probe displayed unique selectivity on HPO42− anion in medium at pH = 11. More importantly, the probe could open a new platform in Q[n]-chemistry, that is the Q[n]-based host–guest interaction systems can apply in anion recognition or response.