jimmyboy - 27-3-2004 at 12:09
I was recently thinking about this and wondering if there was such an animal - I know that there are dyes that can change color with temperature - but
are there any substances that are relatively stable in low light conditions but change color or even ignite under sunlight or a light bulb? could
anyone give me a few examples - would they be fairly easy to make?
not counting silver salts of course
[Edited on 27-3-2004 by jimmyboy]
Esplosivo - 27-3-2004 at 12:56
I don't know if I understood you well. Are you speaking about any photochemical reaction, or just a specific group where useful compounds are
synthesized.
A mixture of equimolar proportions of chlorine and hydrogen will be stable when in the dark, but if exposed to ultraviolet (or any light for that
mater), the Cl will form free radicals and an explosive reaction will occur. Chlorine often undergoes this free radical formation when reacting, such
as with alkanes. Other elements, such as halogens, react in this way but their rate of reaction might vary.
Here are a couple of interesting sites:
Photochemical reactions of organic compounds (which might prove interesting to most):
http://www.infochembio.ethz.ch/links/en/physchem_photochem_r...
Basic reactions involving silver:
http://www.wcsscience.com/photochemical/reactions.html
guaguanco - 27-3-2004 at 22:33
There are chemicals (like NCl3) that can explode when subjected to strong light. Does that count?
Esplosivo - 27-3-2004 at 23:47
Read the attached pdf. It contains very good background on photocatalysis, including definition of certain terms which are quite useful.
Define what you intend by your question. What are you asking for exactly? There are too many photo- induced reactions to just discussa and name them
all 
.
Attachment: iupac_photocatalysis.pdf (298kB)
This file has been downloaded 796 times
jimmyboy - 28-3-2004 at 11:13
I'm looking at photochromic compounds/reactions in general -- the ones that im specifically interested in would be one that is stable in the dark
(preferably a solid or liquid at room temperature) but combusts on exposure to light -- the other im looking at is the compound in "bloody
soap" - its basically some white soap that when turns your skin and everything you touch dark red when you use it.
Esplosivo - 28-3-2004 at 22:32
The production of such chemicals depends on what the availability of chemicals you have. A simple search on google yields a lot of results. Some of
the named chemicals are not that difficult to produce. The problem is obtaining the reagants.
Check out this site:
Prep. of photo- and piezo- chromic compounds
http://www-class.unl.edu/chem254/Lab10/
Btw, does the soap you named simply stain your skin when it is applied in the presence of light, or does it stain it also in the dark?
jimmyboy - 28-3-2004 at 22:47
the soap im pretty sure is a base-acid reaction of some sort - no light needed there.
Esplosivo - 28-3-2004 at 23:06
Just another question. Is the dye removed simply by washing in water, or in some organic solvent say EtOH?