Access Type

Open Access Dissertation

Date of Award

January 2022

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Aaron S. Rury

Abstract

This dissertation will discuss the photophysics of metalloporphyrins, mainly CuTPP, ZnTPP, and H2TPP under strong light-matter coupling conditions. Strong light-matter coupling was achieved by embedding the previously mentioned chromophores into a spun coated PMMA polymer coating which is then incorporated as a spacer layer in a FabryPérot nano-cavity. The cavity thickness is chosen so that the cavity photon is of similar energy as the B, or Soret transition (2nd excited state) of the porphyrin molecule. The exchange of energy between the cavity photon and the molecular mode leads to the formation of polariton states.

Increasing the concentration of the molecules leads to an increase in the Rabi splitting, or the splitting between the polariton states. By increasing the Rabi splitting the lower polariton is pushed closer in energy to that of the porphyrin’s 1st excited state (Q band). By doing this we observe an increase in the rate of nonradiative relaxation between theLP and the 1st excited state of ZnTPP. However, this rate does not follow the established gap law. We attribute this to interpolariton decay channels which play an important role in determining the dynamics of polaritons.

We also observe an increase in CuTPP emission in the region of the 1st excited state under strong light-matter coupling conditions. By constructing a set of multi-layer cavities we are able to account for the Purcell effect which may be responsible for this feature. We determine that using the CuTPP Soret band to form polaritons also produces a lower lyingpolariton state slightly below the Q band. We attribute this to vibronic coupling between the Q band and the now hybridized B band (S2 state) of our cavity system. Moreover, we observe that the emission from this state is greatly amplified when the energy difference between the lower lying ν2 cavity mode and the HT polariton matches the vibration energy of the collective vibrational states.

We extend the multi-layer cavity system to include a layer of H2TPP, whose Soret band is nearly degenerate with that of CuTPP. Using a 3x3 oscillator Hamiltonian we determine that despite their near degeneracy, the resulting polaritons inherit unique excitonic characteristics. We observe that the lower polariton is dominated by the H2TPP exciton fraction,while CuTPP is the dominant exciton fraction in the upper polariton. Moreover, we determine that the photonic contribution to the middle polariton is small at all angles. We also observe a narrowing of the lower polariton lineshapes near the resonance angles, suggesting that polariton motional narrowing must be considered when modeling the dynamics of molecular polaritons.

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