Signatures of Plexcitonic States in Molecular Electroluminescence

Justin P Bergfield,Joshua R Hendrickson

doi:10.1038/s41598-018-19382-2

Justin P Bergfield, Joshua R Hendrickson

Open Access

https://doi.org/10.1038/s41598-018-19382-2

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Abstract

We develop a quantum master equation (QME) approach to investigate the electroluminesence (EL) of molecules confined between metallic electrodes and coupled to quantum plasmonic modes. Within our general state-based framework, we describe electronic tunneling, vibrational damping, environmental dephasing, and the quantum coherent dynamics of coupled quantum electromagnetic field modes. As an example, we calculate the STM-induced spontaneous emission of a tetraphenylporphyrin (TPP) molecule coupled to a nanocavity plasmon. In the weak molecular exciton-plasmon coupling regime we find excellent agreement with experiments, including above-threshold hot luminescence, an effect not described by previous semiclassical calculations. In the strong coupling regime, we analyze the spectral features indicative of the formation of plexcitonic states.

Highlights

We develop a quantum master equation (QME) approach to investigate the electroluminesence (EL) of molecules confined between metallic electrodes and coupled to quantum plasmonic modes
As a first test of our theory, we investigate the scanning tunneling microscope induced luminescence (STML) of a tetraphenylporphyrin (TPP) molecule coupled to a single quantum plasmon mode
2π i,j (ω − ωji)2 + τj2i where γraj→d i is the radiative decay rate between states j and i, ρss is the steady-state solution of Eq (7), and τji is the full width at half maximum (FWHM) of the EL

Summary

Signatures of Plexcitonic States in Molecular Electroluminescence

We develop a quantum master equation (QME) approach to investigate the electroluminesence (EL) of molecules confined between metallic electrodes and coupled to quantum plasmonic modes. Dong et al observed molecular hot-luminescence (HL) from excited vibrational modes in tetraphenylporphyrin (TPP) molecules weakly coupled to metallic electrodes[18]. Their data are a direct observation of the strong dependence of the EL on the resonant frequency of the localized nanocavity plasmons. We develop a state-based quantum master equation (QME) approach to investigate the EL of molecules in both the weak and strong plexcitonic coupling regimes. Similar methods have been used to investigate plasmon-enhanced EL and transport-induced EL in STML systems before[24,25,41,42], we extend these works to describe the quantum optical regime including a full quantum many-body description of the molecule, plasmon modes, electrodes and their couplings. We simulate the EL of a TPP molecule coupled to a single quantum plasmon mode for several voltages, plexcitonic coupling strengths, and detunings

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