Fluorinated Phenyl Meso-Substituents Regulating Excited State Absorption-Driven Protonation of Free-Base Porphyrins

Excited state absorption (ESA) has been used as a method to controllably induce photo-protonation of porphyrins in chloroform solution allowing the substitution of continuous UV radiation by visible pulsed light (6 ns pulse width). We explore the role of meso-substituents in these photochemical reactions and demonstrate that the number of fluorine atoms linked to the porphyrin's outlying phenyl substituents affects both the protonation formation rate and stability of photo-protonated structures. It is observed that with increasing the number of fluorine atoms the reaction becomes less efficient, and the photo-protonated porphyrins become less stable. Our findings suggest a tuning mechanism to control the ESA-triggered photo-protonation of porphyrins.