Chameleons are absolutely fascinating animals, but contrary to public belief, they do not change their skin color in order to adapt to their surroundings, but rather to express emotions. But in chemistry, there is actually also some kind of chameleon molecule that changes its color according to its surroundings.

Hi Sebastian. Hi Niklas, nice to meet you. Please take the glasses. Okay, thank you. So Sebastian, you can tell me more about why the environment plays such an important role in chemistry. Sure. I will demonstrate it with our molecular switch, Spyroperane, and I will use these three solutions containing equal

amounts of this photochromic substance, and we have to aerate them with UV light. Can you please help me Niklas? I recall, so we can use the UV light to switch the sort of molecule into another, which appears new to us, but right

here I see three different colors. Why is that? I thought you put only one kind of molecule into all of these test tubes. By irradiation, we generated the same substance in all three test tubes, but we used three different solvents. Ah, okay.

The phenomenon to show different colors in different solvents is called solvatochromism. Solvato what? Solvatochromism. It's a phenomenon to show different colors in different solvents. So that means the neighboring particles have an influence on the color we perceive? They have an influence on the photons that are absorbed.

Okay, and what kind of light is being absorbed by these? Look, here is an absorption spectra of the different solutions. The peaks indicate where the absorption is the highest. The more polar the solvent molecules are, the more the absorption maxima are shifted to shorter wavelengths. Okay, and the energy is also different? Yes, you can see here the energy is more, the photons are more energetic, the shorter the wavelengths are.

Ah, I see. In toluene, you can see that the red light is absorbed. In acetone, it's yellow light, and in ethanol, it's green light.

So with the toluene, the red light gets absorbed, that means that the blue color remains? That's right. Ah, now I understand it. But I'm sure you as a chemist can explain this in a lot more detail, can't you? Exactly. Let's go to the board and I explain it to you in detail. Look, Niklas, this is an energy diagram special for you.

Oh, thank you. So what do I see here? You can see here, these are our three solutions, and this is the highest occupied energy level with our electrons, and this is the lowest unoccupied energy level. And here's the energy, and this is the way of the polarity of the solvent molecules.

The energy of the absorbed photons depends on the energy gap between the highest occupied energy level and the lowest unoccupied energy level. Okay, but I see no difference here. They're all the same level.

That's true, but in acetone and in ethanol, the highest occupied energy level goes a little bit down because in these solutions, the dye molecules are a little bit more stabilized by the solvent molecule than in toluene.

That means this goes a little bit down and this goes further down, and so the energy gap between the highest occupied energy level and the lowest unoccupied energy level increases. Okay, so let me summarize. The dye molecule's environment determines the color we observe, right?

That's correct. This is the essence of solar autochromacy. We didn't only shoot videos here, but we also prepared a lot of other videos, which you will, as always, find linked below. I hope I'll see you there again. Have a good time and bye-bye.