Abstract
Vibrational strong coupling is emerging as a promising tool to modify molecular properties by making use of hybrid light–matter states known as polaritons. Fabry–Perot cavities filled with organic molecules are typically used, and the molecular concentration limits the maximum reachable coupling strength. Developing methods to increase the coupling strength beyond the molecular concentration limit are highly desirable. In this Letter, we investigate the effect of adding a gold nanorod array into a cavity containing pure organic molecules using FT-IR microscopy and numerical modeling. Incorporation of the plasmonic nanorod array that acts as artificial molecules leads to an order of magnitude increase in the total coupling strength for the cavity with matching resonant frequency filled with organic molecules. Additionally, we observe a significant narrowing of the plasmon line width inside the cavity. We anticipate that these results will be a step forward in exploring vibropolaritonic chemistry and may be used in plasmon based biosensors.
Highlights
Strong light−matter coupling has attracted considerable attention in the past couple of years due to the potential applications it offers in physical and chemical sciences.[1−4] For example, strong coupling of organic molecules has been shown to modify the rate of a photoisomerization reaction,[5,6] increase electronic transport,[7] and expand the length scale of Förster energy transfer.[8−10] Not to mention other effects of strong coupling such as selective manipulation of excited states,[11] suppression of photo-oxidation,[12] or reducing photodegradation in polymers.[13]
We report a method to increase the coupling strength above the limit of C using a hybrid system composed of a Fabry−Perot (FP) cavity, an organic molecule, and a localized surface plasmon in a fashion similar to the one introduced by Bisht et al.[54] using two-dimensional transition metal dichalcogenides in the visible regime
Our hybrid Fabry−Perot cavities show that the addition of a plasmonic array to the standard molecular vibropolaritonic system increases the total coupling strength by almost an order of magnitude for a nitrile absorption band and five times for a carbonyl absorption band
Summary
Strong light−matter coupling has attracted considerable attention in the past couple of years due to the potential applications it offers in physical and chemical sciences.[1−4] For example, strong coupling of organic molecules has been shown to modify the rate of a photoisomerization reaction,[5,6] increase electronic transport,[7] and expand the length scale of Förster energy transfer.[8−10] Not to mention other effects of strong coupling such as selective manipulation of excited states,[11] suppression of photo-oxidation,[12] or reducing photodegradation in polymers.[13]. By fitting the Hamiltonian eigenvalues to the positions of measured transmission peaks (see Figure S6), we obtain the hexanal-cavity system zero-detuning coupling strength (with the seventh FP mode of a 14.25 μm thick cavity) of about 41 cm−1. By fitting the measured dispersion of transmission peaks of the hybrid plasmon−hexanal-cavity system with the Hamiltonian eigenvalues, Figure 4b, we obtain a resonant coupling strength (with the fifth FP mode of a 8.0 μm thick cavity and z = 500 nm) of about 220 cm−1. This addition of the plasmonic meta-atoms does not modify the molecular oscillator strength per se but rather modifies the effective polaritonic spectrum of the hybrid system in the vibrational strong coupling regime This in turn may potentially affect chemical reactions whose rate was claimed to depend on the vacuum Rabi splitting in the recent literature.[30]
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