The vibronic absorption spectra and exciton dynamics of plasmon-exciton hybrid systems in the regimes ranged from Fano antiresonance to Rabi-like splitting.

Abstract

The complex interplay between molecules and plasmonic metal nanoparticles (MNPs) presents a set of particular characteristics in absorption/scattering spectra such as excitonic splitting, asymmetric line shapes, plasmon-induced absorption enhancement and transparencies, etc. Although the MNP-molecule systems have been intensively investigated experimentally and theoretically, the construction of a theoretical framework which can produce all the disparate experimental observations and account for the electron-phonon (e-p) coupling is still in progress. Here, we present a theoretical approach which can account for both the plasmon-exciton coupling and the e-p interaction and produce all the spectral line shapes ranging from Fano antiresonance to Rabi splitting by simply tuning the coupling strength or plasmon damping rate. Additionally, we demonstrate the evolution of vibronic spectra and exciton dynamics with the coupling strength, plasmon damping rate, and detuning energy. It is found that the vibronic structures appearing in Rabi-like spectra are worse resolved, wider, and more largely shifted than those appearing in the Fano regime, attributed to the more significant deformation of the molecular vibrational wavepacket in the Rabi-like regime than that in the Fano regime as the molecular e-p interaction increases. The positive/negative value of detuning energy can induce different degrees of the vibrational wavepacket deformation and subsequently a different effect on the spectra in different coupling regimes.