Assessing Polariton Amended Excited State Photophysics and Structure of Metalloporphyrins using Ultrafast and Nonlinear Optical Spectroscopy

The control of the photophysical and photochemical properties of molecules through truly quantum mechanisms remains an oustanding goal for the chemical physics community. The strong coupling of spatially confined photons to the electrons of molecules appears among the most promising quantum mechanisms test for molecular control. The formation of cavity polaritons through this strong coupling mechanism has been proposed to amend the excited state structure of molecules embedded in electromagnetic resonantors. Despite these proposals, definite experimental evidence of changes to the dynamics and structure of molecular cavity polaritons remain elusive. In this talk I present experimental results demonstrating the ways in which polariton formation amends the dynamics and structure of strongly cavity-coupled metalloporphyrin molecules. First, I examine how the strong coupling of photons in a nanoscale cavity to the Soret resonance of zinc tetraphenylporphyrin (ZnTPP) affects the competition between excited state absorption and fluorescence processes. I show polariton formation incerases the cross section of excited state absorption relative to stimulated emission. Second, I highlight ultrafast spectroscopic results demonstrating the control of energy gap laws via deterministic polariton formation. In particular, these results show the time scale of populating of an excited singlet state of ZnTPP can be controlled through changes to the Rabi splitting. Third, I propose nonlinear optical spectroscopic methods capable of directly assessing the ways the structure of a molecular excited state change in response to polariton formation. These results demonstrate the power of vibrational light scattering spectroscopies to not only assess structural changes central to the proposed control available through polariton formation, but also novel quantum optical phenomena polaritons may enable.