X-ray crystallographic, spectroscopic, electrochemical and computational studies on axially ligation of ZnTPP with pyridine derivative anchored to aza-crown macrocyclic ligand

Abstract

The complexes of zinc tetraphenylporphyrin (ZnTPP) with the azacrown macrocycles bearing pyridine moiety (bp, 1p) as the axial ligand were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR, 1H and 13C NMR, fluorescence, UV–Vis, together with TD DFT calculations. Solution study by employing 1H NMR spectroscopy for ZnTPPbenz and ZnTPPH complexes elucidated that the pyridine moiety was bonded through the fifth-coordination site on the zinc metal atom. The observation of hypsochromic shifts of ca. 15nm for Q(0,1) (the strongest emission) as well as ca. 15nm for Q(0,0) (the second) bands testified to significant difference in the fluorescence of ZnTPPbenz and ZnTPPH. Meanwhile, the absorption spectroscopy signified a bathochromic shift for these complexes in comparison with the ZnTPP. The calculation of association constant for these compounds showed that ZnTPPbenz was more stable complex than ZnTPPH. while the fluorescence studies indicated on thermodynamic similarity of the ligation of ZnTPP with bp and 1p. The electrochemical behavior of these complexes was studied by cyclic voltammetry in CH2Cl2.