Substituted boron subphthalocyanines – Prospective compounds for theranostics: Synthesis, photochemical properties and in vitro cytotoxicity

Boron subphthalocyanines bearing a wide range of functional groups were tested as prospective photosensitizers and fluorophores. Synthetic protocols to novel 4-ethoxycarbonylphenoxy-substituted subphthalocyanine and phenoxy-substituted subphthalocyanine boron phenolate were presented. Differential triplet-triplet absorption spectra of subphthalocyanines were registered and triplet state lifetimes (τT = 0.6 ÷ 3.1 ms) were obtained. The results of flash photolysis measurements predicted the good ability of target subphthalocyanines to produce singlet oxygen and it was supported by the measurements of 1O2 quantum yields (ΦΔ = 0.47 ÷ 0.85). At the same time, satisfactory yields of fluorescence (Φf = 0.13 ÷ 0.50) were observed for most of the subphthalocyanines. The fluorescence decay kinetics were studied to determine the fluorescence lifetimes (τf = 0.30 ÷ 3.05 ns) and confirm the regularities obtained for fluorescence yields. Pronounced fluorescent properties allowed investigating the distribution of subphthalocyanines in the endoplasmic reticulum. In addition, the binding constants with human serum albumin were determined. tert-Butyl- and iodo-substituted subphthalocyanines demonstrated remarkable photocytotoxicity in human epidermoid carcinoma cells at micromolar concentrations. At the same time, target boron subphthalocyanines exhibited low dark cytotoxicity. All mentioned above make boron subphthalocyanines promising candidates as highly effective photosensitizers for photodynamic therapy and fluorescent labels for diagnostic. [Display omitted] •Substituted boron subphthalocyanines show effective singlet oxygen generation.•Substituted boron subphthalocyanines demonstrate bright fluorescence.•Hydrophobic interactions lead to strong binding between subphthalocyanines and HSA.•Subphthalocyanines accumulate in mitochondria and the endoplasmic reticulum.•tert-Butyl- and iodo-substituted subphthalocyaniunes shows micromolar phototoxicity.