Core–shell plasmonic nanostructures to fine-tune long ``Au nanoparticle-fluorophoreʹʹ distance and radiative dynamics

The accurate description of the energy and/or charge transfer mechanism involving Localized Surface Plasmon Resonance (LSPR) is crucial for the research field of plasmonics. The investigation is however frequently hampered by the inaccurate definition of separation distance between the energy and/or charge donor–acceptor pair. Herein we designed and constructed core–shell plasmonic nanostructures to realize precise, long separation distance control between the gold core (energy acceptor) and fluorophores (energy donor). Both steady-state and time-resolved fluorescence measurements were employed to investigate radiative properties of the as-prepared nanosystem. The observed overall fluorescence quenching of the core–shell plasmonic nanocomposites with the decrease of shell thickness is attributed to a concurrent increase of nonradiative rates and decrease of radiative rates with the separation distance decrease. However, neither fluorescence resonance energy transfer (FRET) nor nanometal surface energy transfer (NSET) model is suitable for describing the fluorescence quenching efficiency as a function of separation distance reported in this article. Remarkably, a long-range fluorescence quenching distance of over 34 nm is observed, possibly arising from the coincidence of fluorophore emission wavelength with the plasmon resonance of the gold nanoparticles. This study not only gains insight for designing novel plasmonic devices, but also provides new thoughts for investigation on molecular ruler on a larger measurement scale, molecular beacons and new generation photovoltaics.