Tetraquinoxalinoporphyrazine – π-extended NIR-absorbing photosensitizer with improved photostability

A novel ionogenic water-soluble zinc complex with π-extended ligand – tetraquinoxalinoporphyrazine bearing eight benzoate groups – ZnQPz(COONa)8 was synthesized by template condensation of a new building block, dipentyl 4,4'-(6,7-dicyanoquinoxalin-2,3-diyl)dibenzoate followed by alkaline hydrolysis of ester groups. The photophysical properties of the complex were studied and a significant bathochromic shift of the Q-band by 100 nm was observed as compared to conventional phthalocyanine complexes. However, in contrast to other NIR-absorbing π-extended derivatives with similar optical properties, ZnQPz(COONa)8 showed a high degree of photostability – its photobleaching rate in DMSO was about 3 times lower than that of the zinc tetra-15-crown-5-naphthalocyanate Zn[(15C5)4Nc]. The improved photostability together with the ability to generate singlet oxygen (ФΔ = 0.65 in aqueous DMSO) and absorb light in the near infrared region makes quinoxaline-porphyrazine a good candidate for use in photodynamic therapy. [Display omitted] •Synthesis and characterization of NIR-absorbing water-soluble quinoxalinoporphyrazines.•High quantum yield of singlet oxygen generation in DMSO.•Improved photostability in comparison with naphthalocyanine.•Panchromatic absorbance due to the presence of additional charge transfer band.