Tuning Molecular Emission: Exploring Plasmonic Coupling Effects across High and Low Quantum Yields

The interaction between molecules and plasmonic nanoparticles significantly influences molecular emission properties, offering opportunities to enhance fluorescence through the Purcell effect and strong coupling phenomena. While previous studies have focused on high quantum yield molecules, the role of molecular spectral tuning across varying quantum yield regimes remains underexplored. In this work, we investigate the fluorescence enhancement of molecules coupled to pNPs, analyzing how intrinsic quantum yield, molecular absorption and emission wavelengths, and plasmonic particle properties interact to optimize fluorescence. We establish a clear connection between the particle’s scattering characteristics and the conditions for optimal enhancement, showing that for moderate quantum yields, maximal fluorescence can occur off-resonance. In contrast, for low quantum yields, particle absorption is minimized, and enhancement peaks at plasmon resonance. These insights, supported by examples, provide valuable guidance for designing systems in the near- and mid-infrared, where quantum yield limitations are pronounced due to the energy-gap law. Our findings pave the way for advancements in applications such as fluorescence imaging, light-fidelity communications, and optical security.