Synthesis and Functional Properties of Fluorinated Phosphonate-Substituted Porphyrins: Excellent Photosensitizers and Robust Precursors for Photoactive Langmuir-Schaefer Films.

Fluorinated porphyrins have attracted considerable attention in PDT, sensing and catalysis. Guided by demands for functional porphyrins with tunable electronic properties, high photostability, and controlled supramolecular organization, we report a synthetic approach to meso-tetrakis[4-(diethoxyphosphoryl)-2,3,5,6-tetrafluorophenyl]porphyrin (H2TF4PPP), which combines the advantages of diethyl phosphonate and fluorine substituents within a highly symmetrical porphyrin molecule. X-ray diffraction analysis of H2TF4PPP reveals that diethyl phosphonates govern the crystal packing, while the macrocycles avoid π-π stacking. Zn(II) and Pd(II) complexes with H2TF4PPP were prepared in high yields. In contrast, insertion of In(III) ions exhibiting strong Lewis acidity was accompanied by partial hydrolysis of phosphonate groups. H2TF4PPP and its Zn(II) and Pd(II) complexes efficiently generate singlet oxygen displaying a good solubility in various organic solvents. The noble-metal-free porphyrin H2TF4PPP surpasses Pd(II) complex of non-fluorinated analogue (PdTPPP) in photocatalytic performance, enabling sustainable oxidation of sulfides to sulfoxides with oxygen. H2TF4PPP forms a stable Langmuir monolayer which can be transferred onto solid substrates, yielding dense single-layer films containing fiber-shaped nanoparticles. The films thus obtained are emissive and their photostability surpasses that of H2TPPP films. Water-soluble porphyrins H2TF4PPP-A and PdTF4PPP-A with phosphonic acid groups were also prepared and briefly investigated.