An intramolecular charge transfer based fluorescent probe for imaging of OCl

The discovery and utilization of new fluorescent chromophore is indispensable to exploit high performance probes for biological research. Stokes shift is one of the most important properties of chromophore accounting for super-resolution fluorescence imaging. Intramolecular charge transfer (ICT) is one of the fundamental mechanisms for fluorescence that accompanied by large Stokes shifts. Based on the conformational changes between ground and excited states, ICT models can be divided into two types: conformation-steady ICT, whose conformation remains unchanged, and conformation-changeable ICT, which is characterized by the rotation of the chromophore around an axis upon excitation. Herein, we report a new chromophore whose donor and acceptor parts took a butterfly geometry with a dihedral angle of 21° in ground state and a planar conformation upon photo excitation. The bent conformation might be ascribed to the extra conjugated double bond, which made the coplanarity of the chromophore in ground state get worse. The chromophore shows a remarkable Stokes shift over 150 nm and a high fluorescence quantum yieldof 0.62. The limit of detection is 41 nM, which enabled the imaging of basal as well as induced OCl^- in different cells. Moreover, the pronounced spectroscopic properties ensure the in vivo monitoring of OCl^- in arthritic mice. This finding would shed light on the exploitation of small molecule probes based on new fluorescence chromophore for precise biological imaging.