Regulating glutathione-responsiveness of naphthalimide-based fluorescent probes by an oxidation strategy

Two naphthalimide-based fluorescent probes containing a thiomorpholine (Np-NS) or a sulfoxide-morpholine (Np-NSO) component are reported. The morpholine unit of non-fluorescent Np-NS and Np-NSO can transform into sulphone-morpholine and be accompanied by blue fluorescence upon oxidative stress, ascribed to the formation of sulphone-morpholine on probes. This sensing behavior displays that they can selectively respond to glutathione to generate a green emission by a sulfonamide-based detection moiety both in vitro and in living cells. Interestingly, the different oxidation states of a sulphur atom on a thiomorpholine ring can be utilized to regulate responsiveness of these probes towards glutathione. Such an oxidation strategy would provide a possibility for enhancing the response rate.