Interrogating the Structure of Molecular Cavity Polaritons with Resonance Raman Scattering: An Experimentally Motivated Theoretical Description

Abstract

The formation of exciton polaritons by strongly coupling molecular electronic transitions to spatially confined photons may change photochemical processes. However, the fundamental physical drivers of these proposed changes remain unclear. To understand the role of changes to the molecular structure caused by polariton formation in these photochemical processes, we develop an experimentally motivated theoretical description of resonance Raman scattering from exciton polaritons. By modeling the structural parameters of light absorption in zinc tetraphenyl porphyrin and exciton polaritons formed from this molecule in nanostructured Fabry–Pérot cavities, we simulate resonance Raman scattering excitation spectra from exciton polaritons and assess how these spectra depend on the polariton characteristics. We find that the detuning of the cavity mode energy from that of the molecular transition can affect the structure of the resulting polaritonic states, as inferred from our simulated spectra. We also find previously unreported interference effects between the quantum paths contributing to the resonance Raman scattering pathways changes in the presence of exciton polaritons. Finally, we discuss possible experimental configurations capable of extracting the predicted polariton spectral signatures from the background of the signal from molecules not participating in strong cavity–molecule coupling. These results suggest resonance Raman spectroscopy could be a powerful tool to assess the role changes to the molecular structure plays in the amended photophysics and photochemistry of exciton polaritons.

Quantum Control of Ultrafast Internal Conversion using Nano-Confined Virtual Photons

“…The parameters of these potential energy surfaces are determined from density functional theory calculations reported in our previous study. 30 As shown in Figure 6, this simple model does not predict a trend in ∆ ν for different collective vacuum Rabi splitting values consistent with the measured internal conversion rate constants. In particular, while our results indicate the internal conversion rates for hΩ/2 = 0.05 eV and 0.07 eV fall below the predictions of Jortner's model, the ∆ ν values we find from our phenomenological model at similar collective vacuum Rabi splitting values should coincide with increases in the internal conversion rate.…”

“…The parameters of these potential energy surfaces are determined from density functional theory calculations reported in our previous study. 30 As shown in Figure 6 Figure 6: The numerically calculated dependence of the dimensionless displacement of the lower polaritonic potential energy surface relative to the S 1 state of zinc tetraphenylporphyrin found as a function of the collective vacuum Rabi splitting energy,hΩ R . The trend found from these numerical calculations does not account for the discrepancies between our measured polaritonic internal conversion decay rates and the rates predicted by standard microscopic physical theories.…”

“…[13][14][15][16][17][18] To assess this idea, we phenomenologically investigated changes to ∆ ν of a single, harmonic mode induced by polariton formation within a framework proposed by Mukamel and co-workers 17 we amend to consider a polyatomic molecule. 30 Using this phenomenological model, we calculate how the S 2 potential energy surface changes upon polariton formation and how these changes affect ∆ ν of the lower polariton relative to the unaffected S 1 state. The parameters of these potential energy surfaces are determined from density functional theory calculations reported in our previous study.…”

Quantum Control of Ultrafast Internal Conversion Using Nanoconfined Virtual Photons

“…In this model, we presume the vibration of interest is a ring distortion possessing an effective frequency of 1190 cm −1 (ℏω ν = 0.1475 eV), given the separation of the peaks in the linear absorption spectrum shown in the left panel of Figure 1 and established previously. 34 We also presume the energy of the S 1 state remains the same relative to the molecule's ground state as we change the collective vacuum Rabi splitting energy. Figure 5 shows the results of this modeling.…”

“…13−18 To assess this idea, we phenomenologically investigated changes to Δ ν of a single, harmonic mode induced by polariton formation within a framework proposed by Mukamel and co-workers 17 that we previously extended to polyatomic molecules. 34 We use this model to calculate how the S 2 potential energy surface changes upon polariton formation and how these changes affect the Δ ν of the lower polariton relative to the unaffected S 1 state.…”