Modeling the near-field effect on molecular excited states using the discrete interaction model/quantum mechanical...

Area of Science:

• Plasmonics
• Quantum Chemistry
• Computational Electrodynamics

Background:

• Strong light-matter interactions alter molecular optical properties near plasmonic nanoparticles.
• Accurate modeling requires explicit description of nanoparticle junctions due to nanoscale dimensions.

Purpose of the Study:

• To develop and test an advanced computational method for modeling plasmonic near-field and molecular excited state coupling.
• To investigate the influence of multiple electronic transitions and intermolecular interactions on molecule-nanoparticle coupling.

Main Methods:

• Utilized the discrete interaction model/quantum mechanical (DIM/QM) method with an atomistic nanoparticle description.
• Extended DIM/QM to incorporate local field effects within the sum-over-state formalism of time-dependent density functional theory.
• Compared the DIM/QM model with the coupled-dipole model (CDM) for interactions between organic chromophores and metal nanoparticles.

Main Results:

• The DIM/QM method accurately models plasmon-molecule coupling, outperforming simpler models like CDM.
• Two-state models were found to be insufficient when plasmon excitation is detuned from molecular excitations.
• Molecule-nanoparticle coupling strength is highly dependent on the specific site of interaction on the nanoparticle.

Conclusions:

• Explicitly describing the nanoparticle cavity is essential for capturing atomistic local field effects in strong coupling regimes.
• The developed DIM/QM method provides a more accurate framework for studying nanoscale light-matter interactions.
• Findings highlight the limitations of simplified models and emphasize the need for detailed computational approaches.