Highly electron deficient tetrabenzoquinone-appended Ni(II) and Cu(II) porphyrins: spectral, solvatochromatic, electrochemical redox and tuneable F- and CN- sensing properties

摘要

Copper(II) or Nickel(II) complexes of 5,10,15,20-tetrakis(3,4-dioxo-5-t-butylcyclohexa-1,5-dienyl)porphyrin (diOxPM, M = Ni, Cu) exhibited a hypsochromic shift in the B-band as compared to the respective 5,10,15,20-tetrakis(3,5-di-t-butyl-4'-hydroxyphenyl) porphyrin (H-2-dtBTPP) and meso-tetrakis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadienylidene) porphyrinogen (OxP). Thorough investigation of the electrochemical properties of diOxPM (M = Ni, Cu), OxP and H-2-dtBTPP lead us to the important observation that the first reduction of diOxPM (M = Ni and Cu) is very much anodically shifted (Delta E-redn = 1.1 V) as compared to that of M-dtBTPP (M = Cu or Ni) due to the presence of the strongly electron withdrawing cyclohexadienyl groups. These electron-deficient meso-tetrakis(3,4-benzoquinone)-substituted Ni(II) and Cu(II) porphyrins exhibited very high binding constants (1.5 x 10(9)-2.5 x 10(7) M-2) with F- and CN- and can be used to distinguish them from other anions by UV-Vis spectrophotometry. Solvatochromism was combined with anion binding in an attempt to provide the axial ligation mechanism of CN- and F- ions. These highly electron deficient porphyrins act as F- and CN- chemosensors in nonaqueous media. However, these porphyrins detect only CN- ions in an aqueous medium but remain insensitive towards F- ions due to high solvation of F- ions in water.