A naphthalimide–rhodamine chemodosimeter for hypochlorite based on TBET: High quantum yield and endogeous imaging in living cells

A naphthalimide-rhodamine fluorescent turn-on probe RHSNO with red emission for hypochlorous acid based on dual reaction linkage induce through-bond energy transfer (TBET) system was designed and synthesized. Rhodamine B thiohydrazide and naphthalimide -N,N- dimethylthiocarbamate (DMTC) were linked to form a structure of monothio-bishydrazide. In addition, introduce dimethylthiocarbamoyl chloride as another reaction site of ClO − , and it acts to quench the fluorescence of naphthalimide. In the presence of ClO − , RHSNO exhibits high selectivity toward ClO − at trace levels over other anions/ROS based on ClO − -triggered intramolecular desulfurization cyclization of rhodamine-thiohydrazide, the spiro ring of rhodamine was opened and meanwhile desulfurization hydrogenation happened at DMTC of naphthalimide moiety. These dual linkage reaction happened simultaneously made a typical TBET process took place from naphthalimide donor to rhodamine acceptor, an obvious increase of rhodamine emission at 590 nm and enhanced up to 260-fold gradually after adding ClO − with the increase of the concentrations. The efficiency of energy transfer was calculated to be 86%. And the quantum yield of rhodamine moiety is 0.64. Besides, the chemodosimeter RHSNO for ClO − with high sensitivity, a dramatic color change from colorless to brightly pink among 2 s after the addtion of ClO − . The detection limit was determined to be 22.1 nM and works excellently within a wide pH range of 5–10. Moreover, RHSNO had been employed for endogenous imaging in MCF-7 cell for ClO − . The results indicated that the probe could permeated into the cells and reacted with the intracellular ClO − . It is excellent to design fluorescence sensor RHSNO as a quick and effective method for detecting excess ClO − in living cell, for maintaining the balance of hypochlorite in the body and ensure normal life activities.