Illumination of 4a and 5a at an activating wavelength () encourages the formation of 4b and 5b, respectively. The photogenerated isomers can be excited selectively with irradiation at an appropriate exciting wavelength () to emit light in the form of fluorescence. Both transformations are reversible. The original nonemissive state 4a is regenerated thermally, while 5a is reformed photochemically.
