We synthesized a photoswitchable fluorescent probe incorporating a
coumarin fluorophore and an oxazine photochrome within the same molecular
skeleton. The visible illumination of this fluorophore-photochrome dyad results
in the excitation of the fluorescent component only if the photochromic element is
activated with ultraviolet irradiation. Indeed, the photoinduced opening of the
oxazine ring bathochromically shifts the absorption of the coumarin fragment
sufficiently to encourage its visible excitation with concomitant fluorescence.
These operating principles translate into fluorescence photoactivation with good
contrast ratio and brightness as well as short fluorescence lifetime. The modular
character and relative simplicity of this synthetic strategy for the assembly of
photoswitchable constructs might evolve into a general design logic for the photoregulation
of the electronic structure of a given chromophore with a photochromic
auxochrome.