Synthesis, Characterization and pH-sensitivity of AIE Emitters Obtained by RAFT Polymerization of Pt(II) Pincer Complexes with Polyvinylpyrrolidon

Two phosphine substituted Pt(II) pincer complexes (Pt1 and Pt2) containing NNC ligands: methyl 6-phenyl-[2,2′-bipyridine]-5-carboxylate (C1) and methyl 6-(4-fluorophenyl)-[2,2′-bipyridine]-5-carboxylate (C2), and diphenyl(vinyl)phosphine were obtained and characterized using mass spectrometry, NMR spectroscopy and XRD crystallography. The complexes are weakly phosphorescent in acetonitrile solution but display stronger emission in solid state, which is critically determined by the mode of molecular packing in crystal cell. Pt1 and Pt2 readily take part in RAFT copolymerization with polyvinylpyrrolidon to give amphiphilic P1 and P2 copolymers containing 6–7 and 3–5 units of the corresponding complexes in the polymeric chains. In DMFA, P2 forms nanospecies where the platinum chromophores aggregate to give strong emission red shift compared to the monomeric complexes due to Pt–Pt bonding in the aggregates. In aqueous solutions P1 and P2 form micelles with the hydrophobic core containing aggregated platinum chromophores emitting in the NIR spectral region. Hydrolysis of the ester group in the NNC ligand in P2 gives a water-soluble phosphorescent emitter with high lifetime sensitivity to pH in biologically relevant interval (pKa = 6.06).