A general strategy to develop fluorogenic polymethine dyes for bioimaging

Fluorescence imaging is an invaluable tool to study biological processes and further progress depends on the development of advanced fluorogenic probes that reach intracellular targets and label them with high specificity. Excellent fluorogenic rhodamine dyes have been reported, but they often require long and low-yielding syntheses, and are spectrally limited to the visible range. Here we present a general strategy to transform polymethine compounds into fluorogenic dyes using an intramolecular ring-closure approach. We illustrate the generality of this method by creating both spontaneously blinking and no-wash, turn-on polymethine dyes with emissions across the visible and near-infrared spectrum. These probes are compatible with self-labelling proteins and small-molecule targeting ligands, and can be combined with rhodamine-based dyes for multicolour and fluorescence lifetime multiplexing imaging. This strategy provides access to bright, fluorogenic dyes that emit at wavelengths that are more red-shifted compared with those of existing rhodamine-based dyes.|Polymethine dyes are bright and red-shifted fluorophores that lack an intrinsic turn-on mechanism, which leads to non-specific staining when applied to biological samples. Now the fluorescence of polymethine dyes was masked through an intracellular cyclization strategy that gets reversed upon binding an intended macromolecular target, providing specificity for live-cell imaging.