Lardon, NicolasWang, LuTschanz, AlineHoess, PhilippTran, MaiD'Este, ElisaRies, JonasJohnsson, Kai2021-10-092021-10-092021-10-092021-09-1510.1021/jacs.1c05004https://infoscience.epfl.ch/handle/20.500.14299/182063WOS:000697286000024Rhodamines are the most important class of fluorophores for applications in live-cell fluorescence microscopy. This is mainly because rhodamines exist in a dynamic equilibrium between a fluorescent zwitterion and a nonfluorescent but cell-permeable spirocyclic form. Different imaging applications require different positions of this dynamic equilibrium, and an adjustment of the equilibrium poses a challenge for the design of suitable probes. We describe here how the conversion of the ortho-carboxy moiety of a given rhodamine into substituted acyl benzenesulfonamides and alkylamides permits the systematic tuning of the equilibrium of spirocyclization with unprecedented accuracy and over a large range. This allows one to transform the same rhodamine into either a highly fluorogenic and cell-permeable probe for live-cell-stimulated emission depletion (STED) microscopy or a spontaneously blinking dye for single-molecule localization microscopy (SMLM). We used this approach to generate differently colored probes optimized for different labeling systems and imaging applications.Chemistry, MultidisciplinaryChemistrynear-infrared fluorophorelive-cellgeneral-methodintramolecular spirocyclizationfluorogenic probesfluorescent dyesrational designnanoscopyproteinsredtext::journal::journal article::research article