Rhenium(I) Block Copolymers Based on Polyvinylpyrrolidone: A Successful Strategy to Water-Solubility and Biocompatibility

A series of diphosphine Re(I) complexes - have been designed via decoration of the archetypal core {Re(CO) (N^N)} through the installations of the phosphines and bearing the terminal double bond, where N^N = 2,2'-bipyridine ( ), 4,4'-di-tert-butyl-2,2'-bipyridine ( ) or 2,9-dimethyl-1,10-phenanthroline ( ) and = diphenylvinylphosphine, and = 4-(diphenylphosphino)styrene. These complexes were copolymerized with the corresponding N-vinylpyrrolidone-based Macro-RAFT agents of different polymer chain lengths to give water-soluble copolymers of low-molecular ) and high-molecular block-copolymers containing rhenium complexes. Compounds - , as well as the copolymers and , demonstrate phosphorescence from a MLCT excited state typical for this type of chromophores. The copolymers and display weak sensitivity to molecular oxygen in aqueous and buffered media, which becomes almost negligible in the model physiological media. In cell experiments with CHO-K1 cell line, and displayed significantly reduced toxicity compared to the initial complex and internalized into cells presumably by endocytic pathways, being eventually accumulated in endosomes. The sensitivity of the copolymers to oxygen examined in CHO-K1 cells via phosphorescence lifetime imaging microscopy (PLIM) proved to be inessential.