  Photoisomerization, i.e., a change of molecular structure after absorption of
a photon, is one of the most fundamental photochemical processes. It can
perform desirable functionality, e.g., as the primary photochemical event in
human vision, where it stores electronic energy in the molecular structure, or
for possible applications in solar energy storage and as memories, switches,
and actuators; but it can also have detrimental effects, for example as an
important damage pathway under solar irradiation of DNA, or as a limiting
factor for the efficiency of organic solar cells. While photoisomerization can
be avoided by shielding the system from light, this is of course not a viable
pathway for approaches that rely on the interaction with external light (such
as solar cells or solar energy storage). Here, we show that strong coupling of
organic molecules to a confined light mode can be used to strongly suppress
photoisomerization, and thus convert molecules that normally show fast
photodegradation into photostable forms.
