Near Infrared bioluminescence imaging with Through‐Bond Energy Transfer Cassette

: A coelenterazine (CTZ) analogue emitting near-infrared (NIR) bioluminescence was synthesized for through-bond energy transfer (TBET)-based imaging modalities. The analogue, named Cy5-CTZ, was prepared by conjugating cyanine-5 (Cy5) dye to CTZ through an acetylene linker. This novel derivative is intrinsically fluorescent and emits NIR-shifted luminescence upon reacting with an appropriate luciferase, the Renilla luciferase. This Cy5-CTZ substrate is optically stable in physiological samples and rapidly permeabilize through the plasma membrane into the cytosolic compartment of live cells.