High-stability NIR-II fluorescence polymer synthesized by atom transfer radical polymerization for application in high-resolution NIR-II imaging

Abstract

Near-infrared II (NIR-II, 1000–1700 nm) fluorescent imaging (FI) has been reported to achieve optical images with higher resolution and deeper penetration. Among the organic NIR-II small molecules, donor–acceptor–donor (D–A–D) type fluorescent agents have shown superior photophysical and biocompatible properties for FI applications but have ongoing limitations, such as the difficulty in further modifying them with drug-carrying functional groups or prodrugs. In this work, three D–A–D type NIR-II fluorophores with electron acceptors of 4,8-bis(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-1H,3H-benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole) (BBT), 6,7-bis(4-(hexyloxy)phenyl)-4,9-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (TTQ) and 4,6-bis(5-bromo-2-thienyl)thieno[3,4-c][1,2,5]thiadiazole (TTDT) have been successfully prepared. Their optical and imaging properties and stability were investigated via theoretical and experimental studies. The results demonstrated that TTDT-SF exhibited good NIR-II imaging ability. Importantly, TTDT-SF showed outstanding stability in an alkaline and redox environment. Subsequently, a stable atom transfer radical polymerization (ATRP) initiator, based on TTDT and its derivative water-soluble fluorescent polymer TTDT-TF-POEGMA, synthesized through ATRP, was successfully fabricated. It was demonstrated that TTDT-TF-POEGMA exhibited excellent fluorescence ability, great water solubility, effective light stability and great potential in tumor FI and image-guided surgery. In a word, this work has developed a new stable initiator with NIR-II fluorescent properties, which provides a platform for the development of water-soluble and multifunctional NIR-II fluorescent polymers for a broad range of applications.