Oxazolochlorins. 11. Tuning the dynamic high pH sensing range of [meso-tetraarylporpholactonato]M(II) complexes by variation of the central metal ion, the aryl substituents, and introduction of a β-nitro group

Based on the high pH-sensing ability of [meso-tetrakis(pentafluorophenyl) porpholactonato]-platinum(II), we investigated the influence of the metal (M = Zn(II), Ni(II), Cu(II), Pd(II), Ag(II), Pt(II)), the aryl group (Ar = C ₆H₅, C₆F₅), and the presence of a β-NO₂ group on the pH sensing range. The syntheses of the novel β-nitroporpholactone derivatives are described, and their regiochemistry deduced by spectroscopic and single crystal X-ray diffraction methods. The UV-vis base titration midpoints for all derivatives were determined in an aqueous solution containing a surfactant, showing that the metal has the least influence, thus identifying a cheaper and easier method to prepare porpholactone M complex-based high pH-sensors. The influence of the pentafluorophenyl groups and the β-nitration were comparable with respect to their ability to increase the nucleophilicity of the porpholactone toward hydroxide, but the optical response for the pentafluorophenyl-substituted derivative were stronger. β-Nitration and pentafluorophenyl-substitution had additive effects.