Photoactivatable Large Stokes Shift Fluorophores for Multicolor Nanoscopy.

We designed caging-group-free photoactivatable live-cell permeant dyes with red fluorescence emission and ∼100 nm Stokes shifts based on a 1-vinyl-10-silaxanthone imine core structure. The proposed fluorophores undergo byproduct-free one- and two-photon activation, are suitable for multicolor fluorescence microscopy in fixed and living cells, and are compatible with super-resolution techniques such as STED (stimulated emission depletion) and PALM (photoactivated localization microscopy). Use of photoactivatable labels for strain-promoted tetrazine ligation and self-labeling protein tags (HaloTag, SNAP-tag), and duplexing of an imaging channel with another large Stokes shift dye have been demonstrated.