Non‐Polaritonic Effects in Cavity‐Modified Photochemistry

Abstract Strong coupling of molecules to vacuum fields is widely reported to lead to modified chemical properties such as reaction rates. However, some recent attempts to reproduce infrared strong coupling results have not been successful, suggesting that factors other than strong coupling may sometimes be involved. In the first vacuum‐modified chemistry experiment, changes to a molecular photoisomerization process in the ultraviolet‐visible spectral range are attributed to strong coupling of the molecules to visible light. Here, this process is re‐examined, finding significant variations in photoisomerization rates consistent with the original work. However, there is no evidence that these changes need to be attributed to strong coupling. Instead, it is suggested that the photoisomerization rates involved are most strongly influenced by the absorption of ultraviolet radiation in the cavity. These results indicate that care must be taken to rule out non‐polaritonic effects before invoking strong coupling to explain any changes of properties arising in cavity‐based experiments.