Near-Infrared Coumarin-Hemicyanine Hybrid Dyes Bearing an Intramolecular Nucleophile for Activatable Fluorescence and Raman Imaging

Coumarin-hemicyanine (CHC) hybrid fluorophores bearing an intramolecular nucleophile have been reported as ratiometric fluorescent probes based on the equilibrium between the π-conjugated open and cyclic closed forms. Here, we report red-shifted CHC derivatives that can serve as scaffold dyes of activated fluorescent probes and activated Raman probes. We prepared a series of cyano-substituted CHC derivatives and found that substitution at C-4 of the coumarin moiety is effective in extending the absorption wavelength. The near-infrared (NIR) emission of these 4CN-CHC derivatives exhibits high tissue penetration. Dual-color imaging with 4CN-CHC enabled ratiometric monitoring of the lysosomal pH changes. Furthermore, the coherent anti-Stokes Raman scattering (CARS) signals of 4CN-CHC derivatives could be regulated by modifying the open/closed equilibrium, and the different patterns of CARS spectra enabled us to perform multicomponent imaging. Thus, these 4CN-CHC derivatives expand the repertoire of functional probes for NIR and multiplexed vibrational imaging.