Novel meso-phenothiazinylporphyrin dyes: Synthesis, optical, electrochemical properties and PDT assay

• One-pot procedures for synthesis of meso-phenothiazinyl-porphyrin dyes.
• Strong UV–Vis absorptions determine dark purple colour of dyes.
• Red-orange daylight fluorescence of dyes.
• Oxidation potentials ranging between 800 and 1400 mV (vs. Ag/AgCl).
• Photosensitizers with photodynamic effects on skin cell lines, upon irradiation with blue or red light.

The synthesis of new chromophore architectures based on arrays of phenothiazine and (hetero)aromatic units joint in the meso positions of a porphyrin core (phenothiazinyl A4, phenothiazinyl and (hetero)aryl: AB3trans-A2B2 and A3B), is described. The structures were assigned based on HRMS and NMR spectra. Their optical properties were evaluated according UV–Vis spectroscopic data, which emphasized absorption maxima around 420 nm with molar absorptivities 105 M−1cm−1 and emission characterized in solution by large Stokes shifts (3800–4500 cm−1) and fluorescence quantum yields ranging from 0.01 to 0.06. The electron transfer properties of the compounds were estimated using cyclic voltammetry which pointed out three quasi-reversible one-electron oxidations potentials ranging between 800 and 1400 mV (vs. Ag/AgCl). Selected meso-phenothiazinylporphyrins were evaluated as photosensitizers for photodynamic therapy (PDT) by in vitro irradiation of two human skin cell lines (HaCaT and A431) using red and blue light.

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