Unparalleled Ease of Access to a Library of Biheteroaryl Fluorophores via Oxidative Cross Coupling Reactions: Discovery of Photostable NIR Probe for Mitochondria.
The development of straightforward accesses to organic functional materials through C H activation is a revolutionary trend in organic synthesis. In this article, we propose a concise strategy to construct a large library of donor acceptor type biheteroaryl fluorophores via the palladium catalyzed oxidative C H/C H cross coupling of electron deficient 2H indazoles with electron rich heteroarenes. The directly coupled biheteroaryl fluorophores, named Indazo Fluors, exhibit continuously tunable full color emissions with quantum yields up to 93% and large Stokes shifts up to 8705 cm( 1) in CH2Cl2. By further fine tuning of the substituent on the core skeleton, Indazo Fluor 3l (FW 274; lem 725 nm) is obtained as the lowest molecular weight near infrared (NIR) fluorophore with emission wavelength over 720 nm in the solid state. The NIR dye 5h specifically lights up mitochondria in living cells with bright red luminescence. Typically, commercially available mitochondria trackers suffer from poor photostability. Indazo Fluor 5h exhibits superior photostability and very low cytotoxicity, which would be a prominent reagent for in vivo mitochondria imaging.
Journal of the American Chemical Society