Introduction of carboxylic ester and acid functionalities to meso-tetrakis(pentafluorophenyl)porphyrin and their limited electronic effects on the chromophore

• 1–4 Carboxyl and ester groups are introduced into meso-tetrakis(pentafluorophenyl)porphyrin.
• We utilized an SNAr reaction using mercaptopropionates or 3,4-dihydroxybenzoate esters.
• The regioisomeric compounds were spectroscopically characterized.
• The substitution has minimal effects on the porphyrin electronic structure.
• The carboxyl derivatives adhere strongly to TiO2 surfaces.

Alkyl- or aryl-carboxylic acid-functionalized porphyrinic dyes are sought after because of their propensity to adhere strongly to many metal oxide surfaces as required for their application as, for instance, sensitizers in dye-sensitized solar cells (DSSCs), in air purification, or chemosensing systems. The SNAr reaction of the pentafluorophenyl group is a versatile method to introduce functionality into meso-pentafluorophenyl-substituted porphyrins. The conditions to introduce one through four alkyl- or aryl-carboxyl functionalities using mercaptopropionate or 3,4-dihydroxybenzoate esters, respectively, are explored, and the regioisomeric products are spectroscopically characterized. Their saponification to the corresponding carboxylic acids was studied. By experimental determination of their optical properties (absorption and emission spectroscopy) and their frontier orbital positions by cyclic voltammetry, we demonstrate the minimal electronic influence this derivatization method has on the chromophore.

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