The use of a near-infrared RNA fluorescent probe with a large Stokes shift for imaging living cells assisted by the macrocyclic molecule CB7

A near-infrared fluorescent dye Hsd was designed and synthesized, which absorbed as hemicyane and emitted as Cy7 and therefore produced a Stokes shift as large as 224 nm. Quantum chemistry calculation demonstrated that the large Stokes shift was produced by the combination of intramolecular charge transfer (ICT) and internal conversion. Significantly, Hsd showed selectively response to RNA in aqueous solution and fixed cells. Moreover, Hsd could be uptaken into the cells under the assistance of cucurbit[7]uril (CB7) and selectively stain RNA in living cells. The introducing of CB7 provides a platform to amplify the application of some cell-impermeant fluorescent stains through the supramolecular chemistry methods.