Upon addition of CN− increasing from 0 to 100 equiv., a new obvious emission peak centered at 504 nm was observed and obviously enhanced with the increase of CN−. By fluorescence titration, the binding constant between HNA and CN− was etermined to be about (4.571±0.1)×103M−1 and the detection limit of HNA toward CN− was obtained as 4.4×10−6 mol L−1(Supplementary data, Fig. S6), which is sufficiently low for the detection of the CN− found in many chemical systems. And from the mass data for HNA–CN− conjugate, the 1:1 stoichiometry ratio between HNA and CN− was proposed (supporting information Fig. S7). To explore the sensing mechanism between HNA and CN−, the interaction between HNA and OH− was also investigated. Fluorescence emission spectral change of HNA upon addition of OH−
was quite different compared with that of upon addition of CN−,which partially excluded the deprotonation between HNA and CN