Re: Why does chlorophyll & acetone appear purple in white light?

I didn't expect this question! Either you've got an unusual chlorophyll 
extract or your powers of observation are better than mine. In my 
experience, pure chlorophyll samples are green.

First possibility: the chlorophyll is not pure, and has a number of 
accessory pigments mixed in with it, such as xanthophylls and carotenes. 
Xanthophylls are purple, more or less, so this could be the source of the 
colour. Where did the chlorophyll come from? Some plants have very dark 
leaves and are almost black with accessory pigments. Alternatively, autumn 
leaves have lost most of their chlorophyll so the accessory pigments 
dominate. Algae and seaweeds are often not green either.
Most biochemistry texts will have details.

Second possibility: You're seeing chlorophyll's fluorescence. Chlorophylls 
absorb light at 650-700 nm and 400-500 nm. These are red and blue(ish) 
regions, so if you can get chlorophyll to absorb shorter wavelength light 
and re-emit it at these wavelengths, then I guess you'd see something 
purplish. I've never seen this happen, though! Only the red fluorescence 
at 650-700 nm is shown on the first of the sites below:

For absorbance and fluorescence spectra of chl b: http://www.omlc.ogi.edu/spectra/PhotochemCAD/html/chlorophyll-b.html

‘The Physics of Photosynthesis’ has absorbance spectra for chl a and b http://esg-www.mit.edu:8001/esgbio/ps/physics.html

Further background: http://www.ucmp.berkeley.edu/glossary/gloss3/photosyn/pigments.html

Helpful? Ewen