Uploaded September 2016 | Updated September 2026, 1 week ago
Solvatochromism is an interesting property of some dyes showing a different color in various solvents depended on their polarity or elutropy. There are different kids of interactions depending on the dye. To sum it up fast:
For molecules that have a rather ionic structure and composition a solvent with many functional groups, so probably a polar solvent will have a way better interaction will the molecule, just like water and oil don't mix. The color will blue-shift in polar solvents as the absorption level is lowered and more energy is required.
The other possibility is a positive solvatochromism. Here the molecule is rather non-polar.
For Iodine it's a bit more complicated since Iodine should be a non polar. In fact Iodine is a Lewis Acid and will react with electron-donors so Lewis-Bases. Lone pairs on Oxygen and Nitrogen in polar solvents can interact with Iodine as well. The dark purple color of Iodine is caused by a sigma-sigma* - Transition ( literature actually calls it pi-pi* but I think it should be the sigma-bond). If there is no interaction but just dissolution like in non polar solvents the color stays the same so purple. As it becomes more and more polar the color changes to a yellow.
For a better explanation on the real effects in solvatochromism:
DOI: 10.1021/jp1097487
Solvatochromism is an interesting property of some dyes showing a different color in various solvents depended on their polarity or elutropy. There are different kids of interactions depending on the dye. To sum it up fast:
For molecules that have a rather ionic structure and composition a solvent with many functional groups, so probably a polar solvent will have a way better interaction will the molecule, just like water and oil don't mix. The color will blue-shift in polar solvents as the absorption level is lowered and more energy is required.
The other possibility is a positive solvatochromism. Here the molecule is rather non-polar.
For Iodine it's a bit more complicated since Iodine should be a non polar. In fact Iodine is a Lewis Acid and will react with electron-donors so Lewis-Bases. Lone pairs on Oxygen and Nitrogen in polar solvents can interact with Iodine as well. The dark purple color of Iodine is caused by a sigma-sigma* - Transition ( literature actually calls it pi-pi* but I think it should be the sigma-bond). If there is no interaction but just dissolution like in non polar solvents the color stays the same so purple. As it becomes more and more polar the color changes to a yellow.
For a better explanation on the real effects in solvatochromism:
DOI: 10.1021/jp1097487
![Copper Chemistry: K3[Cu(NO2)5]](https://i.ytimg.com/vi/zz23zENTWXk/mqdefault.jpg "Copper Chemistry: K3[Cu(NO2)5]
Explanation will follow soon")
