The protonation of methyl phenyl porphyrin isomers was studied through UV-Vis spectroscopy using trifluoroacetic acid (TFA), a strong organic acid. Protonation was achieved by titration of the porphyrin in toluene and toluene/methanol (80:20). A wavelength shift from the free base Soret to the protonated Soret confirms the formation of the dication. The resulting UV spectra were used to calculate an apparent pKa value of each free base porphyrin isomer. The addition of methanol to the porphyrin solution decreased the average pKa values of the Soret and Q-bands for each porphyrin. This could be an indication of a stabilizing monocation, not easily seen in solution.

Protonation of methyl phenyl porphyrin isomers using UV spectroscopy

ACS Spring Meeting 2021

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