Synthesis of water soluble PEGylated (copper) phthalocyanines via Mitsunobu reaction and Cu(I)-catalysed azide-alkyne cycloaddition (CuAAC) click chemistry

Octa-substituted phthalocyanine (Pc) and copper phthalocyanine (CuPc) with different chain lengths of monomethyl ether polyethylene glycol (mPEG) with molecular weights of 350, 550, 750, and up to 2000 g mol(-1) were synthesised through combining a phenolic Mitsunobu reaction with Cu(I)-catalysed azide-alkyne cycloaddition (CuAAC) click chemistry. Analysis by GPC shows that narrow polydispersities (PDI <= 1.2) of the resultant polymeric derivatives can be achieved; photodiode array (PDA) detection confirms the formation of the desired products. The metal-free Pc polymers are clearly distinguished from polymers functionalised with CuPcs. All PEGylated (Cu)Pc polymers are highly soluble in a range of solvents and show no evidence of aggregation in common organic solvents such as chloroform, DCM, THF, etc. with a split intense Q band between 670 and 690 nm for the mPEG-Pc polymers, and a single Q band at 682 nm for the mPEG-CuPc complexes. The UV-Vis spectra of these polymers in water demonstrate that dimeric complexes are formed in all cases with a minor contribution of monomeric also found in octa-substituted mPEG-CuPc products. More remarkably, the PEGylated (Cu)Pcs with different PEG chain lengths exhibit interesting tunable thermal properties as evidenced by differential scanning calorimetry (DSC).