Amino-substituted C-coumarins: Synthesis, spectral characterizations and their applications in cell imaging

Abstract Compact fluorophores are desired for bioconjugation because they minimally perturb the native biological functions of proteins or organelles. However, their absorption and emission wavelengths are typically short and not ideal for practical applications. For example, coumarin is one of the smallest fluorophores with excellent fluorescence properties. However, its potentials in biological applications are limited by its relatively short excitation wavelengths in the UV spectral region. It is the aim of this manuscript to develop coumarin analogs absorbing and emitting in the visible range through rational molecular engineering. We designed and synthesized C-coumarin dyes, and found that their maximal absorption wavelengths fall well within the visible region, rendering them superior for live cell imaging than O-coumarins. The other promising properties of C-coumarins include larger Stokes’ shifts, low cytotoxicity, and high chemostability.