The basicity of a typical octaalkyl substituted porphyrin (octaethylporphyrin – OEP) and meso substituted porphyrin (tetraphenylporphyrin – TPP) was studied using UV-vis spectroscopy. Protonation of the porphyrins was achieved by titrating them with trifluoroacetic acid (TFA). The protonation can be visualized on the UV-Vis spectrometer where a shift to the right from the free base Soret can indicate that the porphyrin is fully protonated. The data from the UV spectra was used to calculate the apparent pKa values associated with each porphyrin. It was found that the average pKa value for the Meso Tetraphenylporphyrin was 3.60, while the average value for the Octaethylporphyrin was 3.67.

Protonation of octaethylporphyrin and tetraphenylporphyrin with trifluoroacetic acid on toluene using UV-Vis spectroscopy

ACS Spring 2022

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