The Job plot revealed a 1:1 stoichiometric ratio between the
Cu2þ ion and 1 (Fig. 3). In addition, the 1:1 stoichiometry of the
1eCu2þ complex was confirmed by ESI-mass spectrometry analysis.
The positive ion mass spectrum indicated the 1:1 binding model
between 1 and Cu2þ [m/z 420.1; calcd, 420.1] as shown in Fig. 4.
Based on Job plot and ESI-mass data analysis,