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.