A TICT-active orthogonal D-A type probe phenothiazine-BODIPY for ratiometric response of hypochlorite and its application in living cells

A red emissive fluorescent probe 1,7-dimethyl-3,5-bis(4-methoxyphenyl-vinyl)-8-(10-n-butyl-10H-phenothiazine-3-yl)BODIPY 1,7-dimethyl-3,5-bis(4-methoxyphenyl-vinyl)-8-(10-n-butyl-10H-phenothiazine-3-yl)BODIPY (avyl-BODIPY-PTZ) with a special orthogonal donor-acceptor structure was designed and synthesized for rapid, sensitive, and selective discrimination of ClO−, over other reactive oxygen species and anions. The probe displays a linear ratiometric absorption (A578/A640) and fluorescence (F599/F660) response toward ClO− with a fast response velocity (~10 s). The limit of detection (LOD) for ClO− was obtained as 22.6 nM from the fluorescence titration experiment. The fluorescence enhancement of the probe can be observed from the 32-fold enhancement in ratiometric value (F599/F660) and the increasement of quantum yield from 0.01 at 660 nm to 0.28 at 599 nm. The oxidation of S atom in phenothiazine by ClO− to form the sulfoxide-type structure was proposed as the recognizing mechanism according to the Mass spectral analysis. The ratiometric enhancement of fluorescence was rationalized by the theoretical calculations. The orthogonal donor-acceptor structure according to optimized calculation and solvent effects of avyl-BODIPY-PTZ illustrated that the ClO− oxidation induced conversion from the nonradiative TICT process to the radiative LE process and caused the fluorescence ratiometric enhancement. The probe with low cytotoxity can successfully permeate into living cells and the cell images can be achieved in single channel. Moreover, after addition of ClO−, another bright red emission channel of the probe switched on and the probe displayed two-channel emission in living cells.