Collective Effects in Polariton Chemistry and Photophysics

Coupling molecules to the quantized radiation field inside an optical cavity creates a set of new photon–matter hybrid states, so-called polaritons. Recent experiments have demonstrated that molecular polaritons can lead to modifications of excited-state dynamics and spectroscopy, photochemistry, and ground-state chemical reactivities. We review the fundamental theory of molecular polaritons under collective light–matter coupling, where many molecules are simultaneously coupled to the cavity mode. Our discussion is based on model systems that effectively capture the essential physics of experiments, allowing one to obtain analytic theories and valuable insights into the microscopic mechanisms in polariton dynamics and spectroscopy, photochemistry, and vibrational strong coupling–modified chemistry.