Well-Defined Segment of Carbon Nanotube with Bright Red Emission for Three-Photon Fluorescence Cerebrovascular Imaging

Abstract

As the shortest segment of carbon nanotubes (CNTs), cycloparaphenylenes (CPPs) offer a well-defined alternative for CNTs as the fluorophores in bioimaging. However, most of CPPs emit blue or yellow light, the bright red-emitting CPP materials required by bioimaging, particularly in vivo imaging, are still lacking. Here, it is shown that a CPP (TB[9]CPP) with red emission up to 650 nm is successfully synthesized and characterized. The fluorescence quantum yields of TB[9]CPP are measured up to 44% in chloroform and 17% as nanodots in aqueous media. Meanwhile, the water-soluble nanodots present outstanding three-photon fluorescence performances, thereby are utilized for in vivo probing of brain vessels by three-photon fluorescence microscopic imaging technique, exhibiting a high penetration depth, good resolution, and clear image contrast.