No-wash live cell imaging of the nucleus with a Si-Bridge dye. Fluorogenic spirolactonizable Si-rhodamines are particularly valuable for no-wash live cell imaging, as the neutral cellpermeable form can convert to a highly fluorescent form when bound to particular targets, such as DNA or the protein HaloTag. This fluorogenic response occurs when the nonfluorescent spirolactone ring opens, generating a zwitterionic dye. To date, all examples of fluorogenic Sirhodamine dyes have been modified with targeting groups directly on the pendant phenyl ring that forms the spirolactone (Figure ). A priori, it was not obvious whether this same fluorogenic behavior would also occur with dyes that are modified with targeting groups on the more distal silyl group.