The possible reaction mechanisms of the compounds to Cu2+ and
CN− are shown in Fig. 4. Two carbonyl groups and one amine group in
one sensor molecule may complex with one copper ion to form 1:1
complex, which induced to the decrease of fluorescence. The in situ 1H
NMR spectra of compound 1 in CD3CN upon the addition of cyanide anions
are shown in Fig. S7. FromFig. S7, one can see that after the addition
of cyanide anions, the original proton signal of C4 position in coumarin
at 8.71 ppm disappears and a new proton signal at 4.88 ppm appears,
which indicates that typicalMichael addition reaction between cyanide
and compounds occurs and cyanide is bonded to 4-position of coumarin
and then leads to the opening of the double bond.