Appl. Phys. Lett. 103, 221115 (2013)
Martti Pärs and colleagues from the University of Bayreuth in Germany have fabricated an optical gate for controlling the fluorescence emitted from a chromophore. This approach allows the emission of millions of photons to be modulated by the absorption of just tens of photons. It relies on creating a molecular triad that combines two fluorescent molecules of perylene bisimide with the photochromic molecule dithienylcyclopentene. On illumination with ultraviolet light (wavelength, 280–350 nm), the dithienylcyclopentene undergoes photocyclization from an open form to a closed form, suppressing fluorescence from the perylene bisimide. Exposure to red light reverses this effect. The modulation depth of the fluorescence can thus be controlled by varying the intensities and exposure times of the ultraviolet and visible control beams. Fluorescence with a contrast ratio of over 80% is possible. The optically controlled gating is relatively slow (hundreds of milliseconds), but the team says further research should enable much faster operation rates to be realized.
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