Synthesis, photophysical properties and in vitro photodynamic activity of axially substituted subphthalocyanines

Abstract

A new series of subphthalocyanines substituted axially with an oligoethylene glycol chain [SPcB(OCH₂CH₂)_nOH, n = 3 (2) or 4 (3)] or a p-phenoxy oligoethylene glycol methyl ether chain [SPcBOC₆H₄(OCH₂CH₂)_nOCH₃, n = 2 (4) or 3 (5)] have been synthesised by substitution reactions of boron subphthalocyanine chlorideSPcBCl (1) with the corresponding oligoethylene glycols, and characterised with various spectroscopic methods and elemental analysis. The molecular structure of one of these compounds (subphthalocyanine 4) has also been determined. As revealed by absorption spectroscopy, these compounds are essentially non-aggregated in DMF. The low aggregation tendency of these compounds results in a strong fluorescence emission and high efficiency to generate singlet oxygen. All these subphthalocyanines, being formulated with Cremophor EL, function as efficient photosensitisers and exhibit a high photocytotoxicity against HepG2 human hepatocarcinoma and HT29 human colon adenocarcinoma cells. The phenoxy analogues 4 and 5 show a relatively high photostability and are particularly potent towards these cell lines, with IC₅₀ values down to 0.02 µM.