Visible light excitation of the surface plasmon (SP) of silver nanoplates (AgNPs) on a thin polymer film can effectively localize and concentrate the excitation power within volumes of nanoscaled dimensions. The light confinement effect and the enhanced reaction field can be used to increase the cross-section of organic molecules for multiphoton absorption. We report the plasmon-assisted two-photon isomerization of a photochrome-fluorophore dyad, designed to switch reversibly between a nonfluorescent and a fluorescent state in response to the photochromic transformation. The switchable assembly consists of a photochromic oxazine chemically conjugated to a coumarin moiety. We demonstrate that the two-photon ring opening reaction and the subsequent activation of the fluorescence at 685 nm of the photogenerated isomer can be performed by visible laser illumination of the SP of AgNPs, and that the process can be exploited for the detection of single molecules with improved resolution and localization power. Within the resulting system, a single laser operating at 633 nm can be used both for activation (?Ac) and excitation (?Ex) of the emissive isomer at the nanometer scale, reducing the time of the experimental protocol and the instrumental cost. 

Two-photon fluorescence activation at single molecule level with a plasmonic nanoswitch

246th National Meeting (2013)

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