Comment on “Non‐Polaritonic Effects in Cavity‐Modified Photochemistry”: On the Importance of Experimental Details

Recently, an article by Barnes and co-workers reported an in-depth experimental re-evaluation of the earlier work on photoisomerization reactions inside optical cavities under conditions of strong light-matter coupling. That earlier work, which constituted the first demonstration of 'polaritonic chemistry', associated cavity-induced modifications of photoisomerization rates with the emergence of strong light-matter coupling (and the formation of polaritonic states). Barnes and co-workers instead found that cavity-induced changes in light absorption can account for changes in the photochemical reaction rates. While Barnes and co-workers correctly highlight the importance of controlling irradiation conditions from sample to sample where optical cavities are involved, this comment aims to emphasize the great length the original study went to ensure exactly this. The original experimental methods are summarized to point out the significant differences between them and those conducted by Barnes and co-workers. Furthermore, the importance of monochromatic photoexcitation at an isosbestic point rather than using broadband (UV through to IR) irradiation, as well as the careful control for photon flux reaching the molecular layer in all samples, as per the original work, is discussed. Further examination of important issues facing this new and developing domain of Physical Chemistry, is anticipated.