Sciencemadness Discussion Board - Thermochromism at human body temperature?

Thermochromism at human body temperature?

Radiums Lab - 9-7-2025 at 01:02

Hi guys, so I was recently working with some ZnO and TiO2 which had a beautiful colour changing effect.

I am aware that HgI2, ZnS etc. do the same thing.

My question is :
Are there any compounds which exhibit thermochromism at human body temperatures(preferably inorganic ones).

I was struck with this idea when my gallium melted in a sealed vial due to the heat of my hand.

Radiums Lab - 9-7-2025 at 01:51

Please note that the examples which I gave change colour at high temperatures.

[Edited on 9-7-2025 by Radiums Lab]

bnull - 9-7-2025 at 03:01

Check mood rings.

phlogiston - 9-7-2025 at 03:18

There must be, because there are lots of products that produce a range of colors at this range. Mouse pads, etc.
a friend also used to have a thermochromic-paint-based thermometer sticker on an aquarium, which IIRC was around the 30 degree C range, so it changes colors between room temperature and human body.

Radiums Lab - 9-7-2025 at 03:48

Thank you @phlogiston and @bnull for replying, after a bit of digging I failed to find material used

Fulmen - 9-7-2025 at 05:09

You can't have tried that hard: https://en.wikipedia.org/wiki/Thermochromism

First image on the page: https://en.wikipedia.org/wiki/File:Liquid_crystals.webm

Radiums Lab - 9-7-2025 at 07:17

@Fulmen thank you for the link(how did I miss wiki). Any inorganic compounds which show the same?

Fulmen - 9-7-2025 at 07:50

I have no idea. These liquid crystals have been around for decades, but i have never heard of anything else that does anything similar.

bnull - 9-7-2025 at 15:11

It seems that inorganic substances need higher temperatures to show thermochromism. Aqueous dichromate/chromate and alcoholic copper(ii) chloride (I believe aqueous too) change color if you heat them. I considered making sealed samples to use as thermometers for test tubes but never got around to measure the temperature range. Copper(i) iodide gets orange or yellow above 60 °C.

Radiums Lab - 10-7-2025 at 22:41

Hi bnull, so can we conclude no such inorganic salts exist showing thermo. at human temperature.

bnull - 11-7-2025 at 06:41

I didn't say that. There may exist at least one inorganic substance, in solid state or in solution, that changes color at 30-40 °C. The thing is, I don't know such substance but I can't rule out its existence. I'd bet on transition metal salts, either pure or combined with other salts, oxides included (remember the superconductors, they're usually mixed oxides).

Radiums Lab - 11-7-2025 at 07:12

Chat gpt and wiki don't have any answers about an inorganic version so I think it's time for a new discovery.

Reminds me of that potassium metal thread.

Lionel Spanner - 11-7-2025 at 08:30

I found at least one example of organic thermochromism, due to keto/enol tautomerism, though it occurs over a wider range of temperatures.
https://www.nature.com/articles/171222a0

Radiums Lab - 11-7-2025 at 21:56

Yea you are right there are many organic ones but they are not easy to synth that is why Inorganic .

chempyre235 - 12-7-2025 at 05:27

It seems that several alkyl ammonium tetrahalonickelate salts are thermochromic near room temperature, with [(Me)₂NH₂]₂NiCl₄ transitioning at 110°C. Nickel can form these salts with any halogen, and some pseudohalogens. Not 100% inorganic, but the anion is, at least. Besides this, Et₂N can be had relatively simply from hydrolysis of DEET.

Quote:

Organic ammonium salts of the type (R₃NH)₂NiCl₄ are often thermochromic (R = Me, Et, Pr)...The corresponding tetrabromonickelates are also thermochromic with a lower transition temperatures.

Copper salts appear to react similarly to nickel ones, and at least one cuprate, (Et₂NH₂)₂CuCl₄, is thermochromic at even lower temps. Additionally, it seems that zinc and other transition metals (Mn, Fe, Co, Cd and Hg) form these tetrahedral, tetrahalogenic anions in much the same way. Might be worth investigating.

https://en.wikipedia.org/wiki/Thermochromism
https://en.wikipedia.org/wiki/Tetrachloronickelate
https://en.wikipedia.org/wiki/Transition_metal_chloride_comp...

[Edited on 7/12/2025 by chempyre235]

Radiums Lab - 12-7-2025 at 21:26

Yea Ni compounds should be looked into.

Neal - 14-7-2025 at 11:36

Surprised no 1 said cobalt chloride. Blue/pink. But it has to be in HCl or acid though.

Radiums Lab - 14-7-2025 at 13:11

Temperature at which colour changes?

j_sum1 - 14-7-2025 at 16:26

Quote: Originally posted by Neal

Surprised no 1 said cobalt chloride. Blue/pink. But it has to be in HCl or acid though.

Yeah, but that would be an equilibrium between two different complex ions. Colour change for sure, but not thermochromism.

Neal - 14-7-2025 at 17:55

Quote: Originally posted by j_sum1

Quote: Originally posted by Neal

Surprised no 1 said cobalt chloride. Blue/pink. But it has to be in HCl or acid though.

Yeah, but that would be an equilibrium between two different complex ions. Colour change for sure, but not thermochromism.

So the temperature changes the pH, which changes the color? I see. I was wondering if the HCl is acting like a sensitizer.

DraconicAcid - 14-7-2025 at 19:06

Quote: Originally posted by Neal

Quote: Originally posted by j_sum1

Quote: Originally posted by Neal

Surprised no 1 said cobalt chloride. Blue/pink. But it has to be in HCl or acid though.

Yeah, but that would be an equilibrium between two different complex ions. Colour change for sure, but not thermochromism.

So the temperature changes the pH, which changes the color? I see. I was wondering if the HCl is acting like a sensitizer.

No. You have the equilibrium along the lines of
[Co(H2O)6]2+ + 2 Cl- <===> [Co(H2O)2Cl2] + 4 H2O
(octahedral, pink) (tetrahedral, blue)

You need a high concentration of chloride ion to get reasonable concentrations of the tetrahedral complex, but the equilibrium constant is temperature-dependent. You can add chloride until the solution is purple, then heat it up to turn it blue, or cool it down to make it pink.

Fulmen - 21-7-2025 at 05:00

Apoptosis just dropped a video on inorganic thermochromics:

https://www.youtube.com/watch?v=GvcXcOpuEec

Nothing within body temperatures though, but 50C isn't half bad either.

Radiums Lab - 21-7-2025 at 07:07

Yea Fulmen thank you for notifying me about his recent vedio, so 50 degrees is pretty close. The vedio is pretty cool.

Fulmen - 21-7-2025 at 10:03

Just don't poison yourself, mercury compounds are nasty.

Lionel Spanner - 21-7-2025 at 11:02

For what it's worth, when I carried out a Jones oxidation of an alcohol to an acid, back in my first year of university (20 years ago) I ended up with a thermochromic impurity, which was red around 80 °C and green near room temperature.
This was a chromium compound of some kind, for sure - but I don't remember what the alcohol was, so when all's said and done, this post is not actually very helpful.

Radiums Lab - 21-7-2025 at 14:10

@Fulmen thank you for the safey suggestion. I've worked with the metal before but not its comp.

Radiums Lab - 21-7-2025 at 14:15

I am aware that Hg salts(especially soluable ones) are more toxic than Hg metal.

Radiums Lab - 21-7-2025 at 14:20

I will try to make Ag[HgI4] in the near future. Sorry for 3 posts but my device wont support long...

Neal - 21-7-2025 at 18:02

Quote: Originally posted by Lionel Spanner

For what it's worth, when I carried out a Jones oxidation of an alcohol to an acid, back in my first year of university (20 years ago) I ended up with a thermochromic impurity, which was red around 80 °C and green near room temperature.
This was a chromium compound of some kind, for sure - but I don't remember what the alcohol was, so when all's said and done, this post is not actually very helpful.

@Lionel Spanner did it have yellow and orange in between from green to red?

chempyre235 - 22-7-2025 at 07:54

Quote: Originally posted by Fulmen

Apoptosis just dropped a video on inorganic thermochromics:

https://www.youtube.com/watch?v=GvcXcOpuEec

Nothing within body temperatures though, but 50C isn't half bad either.

This seems to confirm that the thermochromism of these salts is related to the specific tetrahedral structure of the anion. Copper, nickel and mercury all display thermochromism with similar anions, and are in the +4 oxidation state, with the anion being in the -2 state. Additionally, these all bear four halogen atoms, and the choice of halogen seemingly has a direct impact on the transition temperature of the salt (F > Cl > Br > I).

This leads me to have a few questions:

Have the other metals I mentioned: Mn, Fe, Co, Cd, (which all form tetrahedral complexes in the +4 state) been tested for this property experimentally?
Is thermochromism of transition metals in this manner limited only to metals that have a tetrahedral +4 state?
Why do different halogens affect transition temperature?
What differences does the choice of cation (e.g., Ag²⁺, Et₂NH₂⁺, etc.) have on the thermochromic properties?
Is there a way to predict what the colors of these salts will be?

[Edited on 7/22/2025 by chempyre235]

Radiums Lab - 22-7-2025 at 08:11

Halogens have different radi thus differdent EN and more the EN, difficult to go to exited state.

Lionel Spanner - 22-7-2025 at 09:27

Quote: Originally posted by Neal

Quote: Originally posted by Lionel Spanner

@Lionel Spanner did it have yellow and orange in between from green to red?

I seem to remember it did - but as it was so long ago and I've never done a Jones oxidation since them, my memory is not 100% reliable.

DraconicAcid - 22-7-2025 at 09:27

Quote: Originally posted by chempyre235

Copper, nickel and mercury all display thermochromism with similar anions, and are in the +4 oxidation state, with the anion being in the -2 state.....

Is thermochromism of transition metals in this manner limited only to metals that have a tetrahedral +4 state?

Why do different halogens affect transition temperature?

What differences does the choice of cation (e.g., Ag²⁺, Et₂NH₂⁺, etc.) have on the thermochromic properties?

The metal is in the +2 oxidation state.

Nickel, at least, generally does thermochromism because it goes from square planar to tetrahedral.

The halogens affect the transition temperature because they have different sizes (larger ones prefer tetrahedral to square planar) and because they have different splitting effects on the orbital (strong ligands split the orbitals more and favour square planar, which is why the cyanides are all square planar).

The cations can have an effect because of their size- they pack differently in the solid state.

Radiums Lab

23-7-2025 at 04:16

Maybe Ag[HgAt4] is the complex i'm looking for

bnull

23-7-2025 at 15:46

Quote:

Maybe Ag[HgAt4] is the complex i'm looking for

Well, I happen to have a kilo of astatine fluoride (AtF) left from an old experiment. It is the only reagent that fluorinates photons, glows in the dark, lots of fun for kids. Free worldwide shipping.

I think this will interest you: Jesse H. Day, Thermochromism of Inorganic Compounds. Chem. Rev. 1968, 68, 6, 649–657, https://doi.org/10.1021/cr60256a001.