The synthesis and optical, electrochemical, and magnetic properties of nickel(II) complexes of 5,10,20-triaryl-5,15-diazaporphyrin (TriADAP) are reported. Metal-templated cyclization of unsymmetrically substituted nickel(II)-bis(1-amino-9-chloro-5-mesityldipyrrin; mesityl = 2,4,6-trimethylphenyl) complexes afforded the corresponding TriADAPs or 5-aryl-15-benzyl-10,20-dimesityl-5,15-diazaporphyrin, depending on the combination of base and solvent. The latter macrocycle was converted to TriADAP by deprotection of the N-benzyl group through Pd/C-promoted hydrogenation. TriADAPs were isolated in both 18π (cation) and 19π (neutral) forms. The interconversion between these two oxidation states resulted in a distinct change in the optical properties of the DAP π-system. NMR spectroscopy of the 18π TriADAP cations showed that they had aromatic character, whereas EPR spectroscopy of the 19π TriADAP showed a highly delocalized electron spin of the π-radical. The para substituents of the N-aryl groups of TriADAPs had a small but distinct impact on their HOMO and LUMO energies. The change in the net charge of one electron was directly reflected in the redox properties of the DAP ring; TriADAP was more easily reduced and less easily oxidized than DAP. The difference in the net charge was also reflected by the shielding of the pyrrolic β-protons observed in the 1H NMR spectra. The present results confirm that TriADAP is a highly promising framework for constructing a new class of azaporphyrin-based materials with 18π-19π redox-switchable optical and magnetic properties.
All Science Journal Classification (ASJC) codes
- General Chemistry