Autocatalytic fluorescence photoactivation.

We designed an autocatalytic photochemical reaction based on the photoinduced cleavage of an α-diketone bridge from the central phenylene ring of a fluorescent anthracene derivative. The product of this photochemical transformation sensitizes its own formation from the reactant, under illumination at a wavelength capable of exciting both species. Specifically, the initial and direct excitation of the reactant generates the product in the ground state. The subsequent excitation of the latter species results in the transfer of energy to another molecule of the former to establish an autocatalytic loop. Comparison of the behavior of this photoactivatable fluorophore with that of a model system and the influence of dilution on the reaction progress demonstrates that the spectral overlap between the emission of the product and the absorption of the reactant together with their physical separation govern autocatalysis. Indeed, both parameters control the efficiency of the resonant transfer of energy that is responsible for establishing the autocatalytic loop. Furthermore, the proximity of silver nanoparticles to reactant and product increases the energy-transfer efficiency with a concomitant acceleration of the autocatalytic process. Thus, this particular mechanism to establish sensitization offers the opportunity to exploit the plasmonic effects associated with metallic nanostructures to boost photochemical autocatalysis.