Abstract
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•Plasmonic effects promote the conversion of photoactivatable fluorophores and enhance emission.•Plasmonic effects allow two-photon fluorescence activation under mild visible illumination.•Plasmonic effects permit autocatalytic photochemical transformations based on energy transfer.
The coupling of visible radiation with the surface plasmon of silver nanoparticles (AgNPs) results in a significant enhancement of the electromagnetic field in close proximity to the surface of the metal nanoconstructs. Such an enhancement can be exploited to operate photoactivatable fluorophores with low illumination intensities, after the sequential absorption of two photons. The first photon converts a nonemissive reactant into an emissive species and the second excites the photochemical product to produce fluorescence. Specifically, either the photolysis of an α-diketone bridge, mounted across positions 9 and 10 of an anthracene chromophore, or the photoinduced opening of an oxazine heterocycle, connected to a carbazole appendage, can be exploited to generate a fluorescent product. The plasmonic assistance of the AgNPs facilitates both photochemical transformations as well as the photophysical processes responsible for the subsequent emission. Furthermore, it also enables the nonemissive reactant to absorb two photons simultaneously and activate the fluorescence of the emissive product, under the influence of relatively low illumination that would, otherwise, be insufficient to ensure efficient two-photon absorption. These operating principles also permit the patterning of fluorescent features with microscaled resolution and, as a result, the optical writing and reading of information with mild illumination. Additionally, the very same plasmonic effects can be exploited to promote the transfer of energy from the fluorescent product to the nonemissive reactant and allow the former species to sensitize its own formation and establish an autocatalytic cycle. Thus, the plasmonic effects associated with AgNPs in combination with the photochemical and photophysical properties of photoactivatable fluorophores offer the opportunity to engineer unique photoresponsive materials that would not be accessible with their separate inorganic and organic components alone.
