Time-dependent quantum/continuum modeling of plasmon-enhanced electronic circular dichroism

Area of Science:

• Computational Chemistry
• Spectroscopy
• Plasmonics

Background:

• Chiral molecules exhibit unique electronic circular-dichroism (ECD) spectra.
• Metal nanoparticles (NPs) can influence molecular electronic properties through plasmonic effects.
• Understanding NP-molecule interactions is crucial for advanced spectroscopy.

Purpose of the Study:

• To present a multiscale real-time approach for studying plasmonic effects on molecular ECD spectra.
• To investigate the influence of a gold nanoparticle on the ECD of chiral molecules like methyloxirane and peridinin.
• To rationalize the observed plasmonic enhancement of ECD signals based on spectral overlap and polarization effects.

Main Methods:

• A quantum-classical approach coupling time-dependent molecular wavefunction evolution with a continuum model for the NP.
• Simulation of methyloxirane and peridinin interacting with a gold NP surface at distances of 1, 3, and 5 nm.
• Analysis of the relationship between the gap of plasmonic and molecular excitation energies and the ECD enhancement.

Main Results:

• No significant plasmonic effect was observed for methyloxirane at any distance.
• A ~20-fold enhancement in the ECD signal of peridinin was observed at 1 nm distance, particularly with linearly polarized light perpendicular to the molecular axis.
• The enhancement correlated with the proximity of the NP's plasmonic peak (around 2.5 eV) to the molecule's electronic excitations.

Conclusions:

• The developed multiscale method realistically describes plasmon-mediated ECD spectra of chiral molecules near NPs.
• Plasmonic enhancement of ECD is significant when molecular and plasmonic excitations are closely matched and coupling is favorable.
• This approach offers potential for studying biologically relevant molecules interacting with nanostructures.