In this case, the changes of -conjugation and internal charge distribution induced by the hydrogen bonds between CN−
and HNA could be responsible for the “turn-on” fluorescence and
the red-shift of emission peak from 462 nm to 504 nm. Absorption
spectral changes of HNA in the presence of various anions provided
further evidence to above speculation. Upon addition of CN−, the
absorption band at 350 nm diminished, while a new red-shifted
absorption band appeared at 450 nm