Photoswitch

Several examples of photochromic compounds include: azobenzene,[6] spiropyran,[7] merocyanine,[8] diarylethene,[9] spirooxazine,[10] fulgide,[11] hydrazone,[12] nobormadiene,[13] thioindigo,[14] acrylamide-azobenzene-quaternary ammonia,[15] donor-acceptor Stenhouse adducts,[16][17] stilbene,[18] etc.

[23] Through chemical modification, red shifting the wavelengths of absorption needed to cause isomerizaiton leads to low light induced switching which has applications in photopharmacology.

[24] When a photochromic compound is incorporated into a suitable catalytic molecule, photoswitchable catalysis can result from the reversible changes in geometric conformation upon irradiation with light.

[25] As one of the most widely studied photoswitches, azobenzene has been shown to be an effective switch for regulating catalytic activity due to its isomerization from the E to Z conformation with light, and its ability to thermally relax back to the E isomer in dark conditions.

[26] One of the more prevalent biological examples in the human body that undergoes structural changes upon light irradiation includes the class of membrane-bound photoreceptors, Rhodopsins.

[29] Rhodopsins are highly efficient photochromic compounds that can undergo fast photoisomerization and are associated with various retinal proteins[30] along with light-gated channels and pumps in microbes.

Fast isomerization allows retinal cells to turn on when activated by light and advances in acrylamide-azobenzene-quaternary ammonia have shown restoration of visual responses in blind mice.

[39] Diarylethenes form stable molecular conduction junctions when placed between graphene electrodes at low and room temperature and act as a photo-electrical switch.

[40] By combining a photoswitch, containing various highest and lowest unoccupied molecular orbital levels in its open and closed geometrical conformation, into a film composed of either p- or n-doped semiconductors, charge transport can be controlled with light.

[44] Incorporation of photoswitching molecules such as donor-acceptor Stenhouse adducts into polymersomes has been used to form nanoparticles which can selectively expose enzymes in response to light, allowing them to mimic some functions of cells.

[53] Pharmaceutical encapsulation and distribution at targeted locations with light has been demonstrated due to the unique change in properties and size of microencapsulated nanostructures with photochromic components.

Photoswitchable Molecules : Upon irradiation with light, photoisomerization occurs, changing the spatial geometry and properties of the molecule.
Photoswitchable Molecules : Azobenzene undergoes a E to Z photoisomerization in which the Z isomer is more polar, has shorter bonds, and a bent and twisted geometry. [ 4 ] Hydrazone undergoes photoisomerization with long thermal half lives of thousands of years. [ 5 ] Spiropyran and Merocyanine undergo ring opening/closing mechanisms upon photo irradiation. Diarylethene and donor-acceptor Stenhouse adducts exhibit changes in color upon photoisomerization. Stilbene is a model photoswitch for studying photochemistry.
Photoisomerization from A to B: The three rates completely describe the isomerization from A to B where Φ A is the quantum yield, I is the photon flux, β is the fraction of photons absorbed by A , N A is the Avogadro constant, V is the volume of the sample. [ 22 ]
Retinal Photoswitch: The absorption of a photon converting cis-retinal to trans-retinal. Once converted, the trans-retinal can disassociate from Opsin. Once converted back to the cis- isomer, it can reform Rhodopsin. [ 27 ]