Rhodamine spirolactam based photoswitches have been extensively applied in super-resolution single-molecule localization microscopy (SMLM). However, the ring-opening reactions of spirolactams are cross-sensitive to acid, limiting their photoswitch use to neutral pH conditions. In addition, the ring-closing reactions of spirolactams are environment-sensitive and slow (up to hours), virtually making rhodamine spirolactams caged fluorescent dyes instead of reversible photoswitches in SMLM. Herein, by introducing hydrogen bonds to stabilize spirolactams, we report a series of acid-resistant rhodamine spirolactams with accelerated ring-closing reactions from fluorescent xanthyliums to non-fluorescent spirolactams, endowing them with good photoswitchable properties even in acidic environments. By further substitution of 6-phenylethynyl naphthalimide on the spirolactam, we shifted the photoactivation wavelength into the visible region (>400 nm). Subsequently, we have successfully applied these dyes in labeling and imaging the cell surface of Bacillus subtilis at pH 4.5 using SMLM.
Bibliographical noteFunding Information:
This work was supported by the National Natural Science Foundation of China (21708039, 21502189, 21878286), CPSF (2017M611278, 2018T110234), and DICP (DMTO201603, TMSR201601, 2015YB07). X. L. and W. C. are indebted to the nancial support from SUTD (T1SRCI17126, IDD21700101, IDG31800104). J. Y. acknowledges the support from the National Research Foundation of Korea (NRF) (No. 2012R1A3A2048814).
© The Royal Society of Chemistry 2019.