Metal or metal-free phthalocyanines containing morpholine substituents: synthesis, spectroscopic and photophysicochemical properties

Abstract

The phthalonitrile (3) and its peripherally tetra 4-(3-morpholinophenoxy) substituted metal-free (4), lead(II) (5) and zinc(II) (6) phthalocyanine derivatives were synthesized. The structures of 3-6 were confirmed by FT-IR, 1H-NMR, MALDI-TOF mass, UV-vis and fluorescence spectral data. The solubility and aggregation behaviors of 4-6 were determined in dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), chloroform (CHCl3) and dichloromethane (CH2Cl2). The observed sharp absorptions were evidence of formation of non-aggregated phthalocyanine species at the studied concentration. The effects of the substituent and central metal ions (metal-free, zinc or lead) on spectroscopic and photophysicochemical properties were determined. Their photophysicochemical properties such as fluorescence quantum yields and lifetimes, singlet oxygen generation and photodegradation quantum yields were investigated in DMSO. The fluorescence spectra of metal-free (4) and lead(II) (5) phthalocyanines were not recorded due to negligible fluorescence emissions of these phthalocyanines. The zinc(II) phthalocyanine (6) had 0.17 fluorescence quantum yield (ΦF) and 1.42 fluorescence lifetime (τF). The phthalocyanines (4-6) had 0.18, 0.41, 0.52 singlet oxygen quantum yields (ΦΔ) and 0.51, 3.90, 0.46 photodegradation quantum yields (ΦΔ), respectively. The zinc(II) phthalocyanine (6) in particular could be a potential Type II photosensitizer candidate for photodynamic therapy in cancer treatment.