Enantiomers are non-superimposable mirror images of chiral molecules, meaning they have the same molecular formula and connectivity but differ in their spatial arrangement. Due to their different spatial arrangements, enantiomers can exhibit distinct photochemical properties, which can be exploited in the field of photopharmacology.The photochemical properties of enantiomers differ mainly due to their interaction with polarized light. When enantiomers absorb circularly polarized light, they can exhibit different absorption intensities, known as circular dichroism CD . This difference in absorption can lead to different photochemical reactions, photostability, and photoproduct formation.In photopharmacology, the differences in photochemical properties of enantiomers can be utilized in several ways:1. Enantioselective drug activation: By using light as an external stimulus, it is possible to selectively activate one enantiomer of a drug while leaving the other enantiomer inactive. This can help in reducing side effects and improving the therapeutic efficacy of chiral drugs.2. Photoswitchable drugs: Some enantiomers can undergo reversible photoisomerization, which means they can switch between their enantiomeric forms upon exposure to light. This property can be used to design photoswitchable drugs that can be turned "on" and "off" using light, allowing for precise spatial and temporal control of drug activity.3. Enantioselective photodegradation: The different photostability of enantiomers can be exploited to selectively degrade one enantiomer in a racemic mixture, leaving the other enantiomer intact. This can be useful for the purification of chiral compounds and the development of enantiomerically pure drugs.4. Enantioselective photorelease: Some enantiomers can be selectively released from a prodrug or drug delivery system upon exposure to light. This can be used to achieve targeted drug delivery and controlled release of chiral drugs.In summary, the photochemical properties of enantiomers differ due to their distinct spatial arrangements and interactions with polarized light. These differences can be exploited in the field of photopharmacology for enantioselective drug activation, photoswitchable drugs, enantioselective photodegradation, and enantioselective photorelease. This can lead to improved therapeutic efficacy, reduced side effects, and better control over drug activity.