High-resolution, single-molecule imaging methods such as PALM and STORM require fluorophores that can be switched on and off on demand. Those methods often rely on fluorescent proteins that photobleach quickly and don't produce as many photons as small-molecule organic fluorophores. A team of chemists led by Stanford University's W. E. Moerner and Kent State University's Robert J. Twieg, report a new photoactivatable small organic fluorophore that's suitable for live-cell imaging (J. Am. Chem. Soc., DOI: 10.1021/ja802883k). The researchers replaced the amine of a red-light-emitting amine-styryl-dicyanomethylenedihydrofuran with an azide group that keeps the fluorophore in a dark state. Illuminating the compound with 407-nm light converts the azide to an amine that fluoresces when excited at 594 nm. The illumination required to activate the fluorescence is mild enough that it doesn't damage cells. The researchers used the label for single-molecule imaging in Chinese hamster ovary cells. They plan to develop targeting strategies to direct the label to specific locations in the cell.