Water-soluble copolymeric materials: switchable NIR two-photon fluorescence imaging agents for living cancer cells

A simple one-pot multi-component ROMP of hydrophilic, spiropyran (SP) and tert-butyloxycarbonyl-protected (Boc-protected) amino-functionalized norbornenes was developed, and a series of water-soluble copolymeric materials were provided. The photochromic SP moiety endows the copolymers the properties of switchable fluorescence imaging with alternating near-IR (NIR) two-photon and visible single-photon excitations; thereby the copolymers can serve as a promising NIR two-photon fluorescent probe for living cancer cells. The cationic ammonium group enhances the cell transporting capability of the copolymers as well. The present strategy of one-pot ROMP also makes polynorbornene a modular and flexible scaffold in designing and synthesizing specifically biocompatible polymers with applications in imaging, diagnosis and therapy.