Polarization- and Angle-Dependent Plasmonic Synchronous Fluorescence Spectroscopy to Probe Molecular Vibrational Couplings on an Aluminum Nano-Film

Probing light-matter interactions at the nanoscale is essential for elucidation of their fundamentals and construction of novel nano-optical devices. In this work, it is proposed that polarization- and angle-dependent plasmonic synchronous fluorescence spectroscopy could be powerful to resolve UV-vis plasmon mediated molecular couplings, even under vibrational sublevels. Taking studies of polycyclic aromatic hydrocarbons (PAHs, one general class of graphene analogs with emission range of 350-550 nm) as demonstration, a simple but efficient device of PAHs nanolayer (with thickness in tens to hundreds of nanometers) on an Al nano-film is fabricated. By synchronously scanning excitation and emission wavelengths in a high resolution to depict polarization- and angle-dependent spectrographic profiles, the vibrational transitions coupled to the Al plasmons could be identified, while these could not be attained by conventional fluorescence measurement. As a result, the featured molecular vibrational couplings for both surface plasmon- and plasmonic waveguide-mediated PAHs-Al interactions have been successfully observed at room temperature. Even toward crowded and overlapped spectral components containing multiple vibrations, the transitions could be individually distinguished. These efforts will contribute to the further exploitation and construction of efficient light-emitting devices via luminant molecules on a metal surface.