A general and highly efficient synthesis of photostable cyanines for super-resolution imaging

Despite their widespread utility in biological imaging, polymethine cyanines—particularly structurally diverse and photostable variants—lack efficient, universal synthetic methodologies. Here, we report a general, one-step strategy for cyanine synthesis via a unique ring-opening reaction of oxazole-aldehydes. This method exhibits click-like kinetics and high efficiency under mild conditions, achieving gram-scale reactions and near-quantitative yield within 240 seconds. We demonstrate exceptional substrate versatility and chain-length tunability by synthesizing 29 distinct cyanines. Critically, the innate amide group on the polymethine chain not only provides a novel handle for site-specific post-functionalization but also dramatically enhances cyanine photostability by up to 2500-fold relative to Cy5.5. These superior photophysical properties enable organelle-specific, multi-color super-resolution imaging (STED/SIM), allowing direct visualization of mitochondrial ultrastructure and real-time fission/fusion dynamics in live neurons. This methodology establishes a general and highly efficient platform for the production of stable and customizable polymethine cyanines, advancing high-performance near-infrared probes for biological imaging.