weakened the binding of between Cu2þ and the withdrawing group
such as the imine group, which results in the increase in the energy
gap of ICT band. Therefore, the large blue shift appeared with the
color change of purple to orange at the first step. Further addition of
CN (more than 3 equiv) formed the stable complex Cu(CN)x and,
concurrently, released the dianionic receptor (12) with an absorption
band at 443 nm