Synthesis, photophysical, electrochemical, and spectroelectrochemical properties of the β-pyrrole functionalized push–pull porphyrins†

Abstract

A set of β-pyrrole functionalized phenothiazine, phenothiazine 5,5-dioxide, carbazole, and ferrocenyl porphyrins 1–4 and their Zn(II) complexes 1a–4a were designed and synthesized via Pd-catalyzed Suzuki cross-coupling reaction. These porphyrins exhibit red-shifted absorption and emission compared to meso-tetraphenylporphyrins. In porphyrin 2, the incorporation of a phenothiazine 5,5-dioxide unit at the β-pyrrolic position led to enhancement in the fluorescence quantum yield (Φ = 0.116) compared to phenothiazine appended porphyrin 1 (Φ = 0.099). The electrochemical analysis of the porphyrins revealed two oxidation and two reduction potentials owing to the porphyrin core, while an additional oxidation wave was observed due to the appended redox entity. Spectroelectrochemical measurements at the first oxidation potential of porphyrins 1–4 displayed a red-shifted Soret band at ∼450 nm along with an increased intensity of the Q-band at ∼670 nm. Computationally optimized structures of porphyrins 1–4 and corresponding Zn(II) complexes 1a–4a revealed that the appended redox moieties exhibit out-of-plane geometry relative to the porphyrin core.