Coumarin-hemicyanine-based far-red to near-infrared fluorescent probes: A new generation of fluorescent probe design platform

As a classical hybrid dye, coumarin-hemicyanine dye has been widely utilized as a remarkably powerful fluorescent imaging tool in the fields of reactive species detection, microenvironment sensing, and biomedical imaging. Compared with the parent coumarin and cyanine dyes, coumarin-hemicyanine hybrid dye has successfully overcome their respective shortcomings and integrated their advantages, such as large Stokes shift, far-red to near-infrared emission, facile synthesis, optical tunability, and inherent ratiometric recognizing ability. Over the past decade, versatile and multifunctional fluorescent probes have been developed to realize biologically reactive species recognition, molecular imaging, and disease diagnosis by employing the unique reactivity of the coumarin-hemicyanine hybrid dye and introducing diverse functional groups into the powerful scaffold. This review focuses on the unique coumarin-hemicyanine-based fluorescent probes and summarizes the recent research advances including design strategies, sensing mechanisms, and biological imaging applications such as the detection of the enzymes, anions, reactive species, microenvironments, and nucleic acid. Finally, the challenges and perspectives of coumarin-hemicyanine dye are also presented. This comprehensive and critical review can broaden the biological applications of coumarin-hemicyanine dye and promote the development of novel powerful molecular imaging probes.