Tunable Wavelength, High-Brightness, and NIR-II Emission Phenanthridinium-Based Heptamethine Dyes for High-Contrast Vascular and Intestinal Imaging In Vivo
Xiaofan He, Jiaying Yu, Jinzhong Hu, Wanying Wei, Kai Sun, Jian Chen, Zhuoer Cai, Min Liu, Yang Xu, Bai‐Wang Sun
Abstract
The second near-infrared window (NIR-II, 900–1700 nm) fluorescence imaging has garnered considerable attention for its deep tissue penetration and high contrast. However, the development of small molecular fluorophores that encompass the NIR-II wavelength, high brightness, and large Stokes shift presents a formidable challenge. Herein, we report a series of phenanthridinium-based fluorophores, named YH dyes, which exhibit high brightness and large Stokes shift. Among these dyes, YH-1c demonstrates the best NIR-II fluorescence quantum yield (2.06% in DMSO) and excellent photostability. As a proof to concept, stunningly rich vascular details in mice were obtained through tail-vein injection of YH-1c NPs, where even under 5-fold magnification, clear visualization of deep abdominal microvessel details down to a diameter of ca. 10 μm was achieved, with a signal-to-background ratio reaching 5.21. This study not only provides a promising tool for high spatiotemporal resolution imaging but also imparts valuable insights for the design of novel NIR-II molecular scaffolds.