Robust route toward cationic phthalocyanines through reductive amination

Abstract

New synthetic pathway toward water-soluble phthalocyanines (Pc) bearing cationic 4-(N,N,N-trialkylammonium-methyl)-phenoxy groups has been elaborated. It involves the convenient reductive amination of various (4-formylphenoxy)-substituted phthalonitriles with diethylamine and NaBH(OAc)3, leading to 3-, 4- and 4,5-(p-diethylaminomethyl-phenoxy)-substituted phthalonitriles as precursors to new Zn(II), Mg(II) and metal-free phthalocyanines (4α-MPc, 4β-MPc and 8β-MPc, M = 2H, Mg, Zn) containing four or eight cationic groups in non-peripheral (α-) or peripheral (β-) positions. Novel compounds have been characterized by different spectroscopic techniques (1H, 13C NMR, FTIR, UV–Vis) and MALDI TOF mass spectrometry. All cationic Pcs exhibited strong absorption in the phototherapeutical spectral range from 670 to 700 nm (εmax > 105 M−1cm−1) and high quantum yields of singlet oxygen generation in DMSO where all phthalocyanines existed in monomeric forms. Also, cationic complexes showed moderate solubility in water with high tendency to aggregation, however α-substituted Zn(II) and Mg(II) complexes existed in water in predominantly monomeric states. Further monomerization of Zn(II) complex 4α-ZnPc in aqueous solution can be achieved by interaction either with non-ionic surfactant Tween-80 or bovine serum albumin (BSA). The advantage of our results is not limited to new convenient synthetic approach to the cationic phthalocyanines but it also consists in preparation of new phototherapeutic agents with promising photophysical and photochemical properties.