Two-photon AIE based fluorescent probe with large stokes shift for selective and sensitive detection and visualization of hypochlorite

We report here a brand new AIE based fluorescent probe (MTPA-Cy) for monitoring the level of ClO−. MTPA-Cy was synthesized via condensation reaction of 3-ethyl-1,1,2-trimethyl-1H-indolium iodide with 4-(bis(4-methoxyphenyl)amino)benzaldehyde, in which indole quaternary salt was incorporated as the mitochondria-target and 4-(bis(4-methoxyphenyl)amino)benzene (TPA) the AIE-active fluorescent reporter. Oxidation by ClO− of the ethylene bridge between TPA unit and indole quaternary salt moiety triggered substantial absorption and fluorescence changes. Upon introduction of ClO−, absorption of MTPA-Cy at 538 nm declined while a new absorption at shorter wavelength around 365 nm developed, manifested by an obvious color change from red to colorless, and fluorescence at 514 nm increased by 16.3-fold under excitation of 365 nm which means a large Stokes shift of ca. 150 nm. A LOD of 13.2 nM was calculated for ClO− in aqueous buffer solution, allowing thereby for detection of ClO− in a wide variety of biological systems. The oxidation product also exhibits two-photon excitation performance since its fluorescence was observed under excitation by an NIR light of 730 nm. MTPA-Cy was applied for detection of ClO− in solution, aggregated forms, solid state and living cells.