Non-fluorescent azido fluorogen which can be photoactivated to the longer wavelength amino version that is fluorescent. Building block and reagent for synthesis of fluorescent probes. Used for the preparation of fluorogenic substrates, chemosensors and probes, which can be concerted to the high fluoresence NBD-amine after release. Fluorescent chemosensor for hydrogen sulfide. Spectral data: Ex=384 (454)nm, Em=550nm.