SiR700-BG is the benzylguanine derivative of SiR700 fluorophore. It emits light in the far-red, it is fluorogenic, highly cell permeable and well suited for STED and SIM superresolution imaging. SiR700-BG can be imaged with a standard Cy5 filterset but using a 700 nm LP emission filter yields better results. It can be used for widefield, confocal, SIM or STED imaging in living or fixed cells and tissue. It is identical to SiR700-BG, used in its original publication in JACS. Benzylguanine (BG) is the substrate of the self labeling tag SNAP-tag™*. Upon reaction with a BG derivative, SNAP-tag™* forms a covalent bond with the substrate and releases guanine. It allows to permanently attach a fluorescent label to any protein of interest (POI) expressed as SNAP-tag™* fusion. *SNAP-tag™ is a registered trademarks of New England Biolabs, Inc.