meso-Tetraarylporpholactones as high pH sensors

The ability of meso-tetra(pentafluorophenyl)porpholactone ((TPL)-P-F) and its Pt(II) complex [meso-tetra(pentafluorophenyl)porpholactonato]Pt(II) ((TPLPt)-P-F) to function as optical high pH sensors is described. Under strongly alkaline or high methoxide conditions, their UV-vis spectra undergo dramatic and reversible red-shifts. The dynamic range for the sensor TFPLPt in solution is from pH 11.5 to 13.2. Using H-1, F-19, and C-13 NMR, UV-vis and IR spectroscopy, mass spectrometry, and the use of model compounds, the molecular origin of this optical shift is deduced to be a nucleophilic attack of OH-/MeO- on the lactone carbonyl of the chromophore, representing a novel mechanism for porphyrin-based sensors. The sensing compound was solubilized with Cremophor EL (R) for use in aqueous solutions and embedded in polymer matrixes for testing as optical fiber-based optodes and planar sheet optode materials.