Chemistry under strong light-matter coupling in cavities

6 problems

• Reproducibility and artifacts in reported cavity rate changes

  Contested

  Several labs that repeated reported cavity experiments saw no change in reaction rate, and others found that small flaws, such as mirrors that are not perfectly parallel or slight heating, can mimic one. The question is which published effects survive careful controls.

• Room-temperature strong coupling and chemistry of single molecules

  Partially resolved

  If a single molecule could mix strongly with light, cavity effects on chemistry could be tested without the problem of sharing among many molecules. Tiny gaps between metal particles (plasmonic nanocavities) have been reported to reach this regime for electronic states of a single molecule, but proof is debated, and for vibrations it is far out of reach.

• Survival of cavity rate effects in the collective coupling limit

  Contested

  In experiments a huge number of molecules share one light mode, so each molecule feels only a tiny part of the coupling. Theory must decide whether any effect on a single molecule's reaction survives this sharing.

• Effect of dark states on cavity-modified photochemistry

  Open

  When many molecules couple to light in a cavity, only a few hybrid states carry the light while most states, called dark states, look like ordinary molecules. It is unclear whether photochemistry can be changed when nearly all excitations end up in dark states.

• Reproducibility of the cavity-modified silane deprotection rate

  Contested

  The first widely cited claim of a dark cavity effect concerned a reaction that removes a silicon-containing group from a molecule. Independent groups have reported different results for the same reaction.

• Do cavity-coupled vibrations change thermal reaction rates?

  Contested

  Experiments report that tuning a mirror cavity to a molecular vibration speeds up or slows down a reaction by factors of several without shining any light. Whether this effect is real and what causes it is unresolved.