Keto‐benzo[h]‐Coumarin‐Based Near‐Infrared Dyes with Large Stokes Shifts for Bioimaging Applications

Fluorescence imaging is a promising tool for the visualization of biomolecules in living systems and there is great demand for new fluorescent dyes that absorb and emit in the near-infrared (NIR) region. Herein, we constructed three new fluorescent dyes (NBC dyes) based on keto-benzo[h]coumarin (k-BC) and benzopyrilium salts. These dyes showed large Stokes shifts (>100 nm) and NIR emission (>800 nm). The relationship between the structures and optical properties of these dyes was further investigated by using density functional theory calculations at the B3LYP/6-3G level of theory. Fluorescence images indicated that the fabricated dyes exhibited good photostability and low cytotoxicity and, thus, have potential applications as imaging agents in living cells and animals.