Photochromism refers to the reversible transformation of chemical species between two isomeric forms with distinguishable absorption spectra upon exposure to electromagnetic radiation like light. Molecules that exhibit photochromism exist in two different isomeric states that can switch between each other under the influence of light or heat through different mechanisms involving electron transfer and transition states. These molecular switches have been investigated for applications like memory devices, molecular motors, and optical and electronic switches due to their ability to undergo efficient and reversible photochemical reactions while maintaining stability for some time.

1. Photochromism
Reversible transformations of a single chemical species upon
electromagnetic radiation where the two states show
distinguishable absorption spectra.
Compound w/c exist in ismeric form separated by uv vis spectra
isomers have diff properties and light source
Interconvert to each others
Compound are photo chromic/switches & process is
hotochromism.
How to ctrl conversion.

2. Molecules, which exist in two different isomers
that can switch from one to another under the influence
of suitable wave length of light/heat.
•For light & heat mechanism/path is diff
• e- trnsfer is there
•Isomer must pass trough transition state
• some try to maintain their properties
Molecular switches

3. Switching is activated by external source
Small organic molecules, capable of undergoing efficient and reversible
photochemical reactions
switch between (at least) two (meta)stable isomers
Stable for sometime not forever
Large impact on the materials world as well biomedical research
Photochromic compounds have been investigated for
•Memory devices
• Molecular motors
•Liquid crystalline materials
•Synthetic ion channels
•Photoswitchable enzymatic systems
•Metal ions extractions
•Electronic and magnetic switches
•Non-linear optical devices
•Logic gates
•Encoder-decoder materials
Application of photoswitches

4. Types of Photoswitches
Cyclophenyldiene
dihydrophane

5. 1.
5.
4.3.
2.
6. Vinyl heptafaluene
Dihydroazaline