Chlorophyll Fluorescence

In a discussion today I was reminded of one of my favorite experiments from college plant physiology class. We were discussing the light harvesting apparatus (LHA) of a plant cell. The molecular organization of this system relies on the primary light collecting molecule chlorophyll. Chlorophyll acts to trap light radiation and convert that into what is called an “excited electron”. This is sort of like electricity. A field of chlorophyll molecules are attached to the chloroplast internal membrane. They pass the excited electrons around until the reach some molecular machines that use that electron to create sugar. The process of making sugar is amazingly complicated, involving a proton gradient, electron carrying molecule (NADPH) and the biological “currency” of the cell, ATP. I’ll spare you the details (for now, moo hoo hah aha ahhaa!).
Anyhow, the interesting thing about chlorophyll in this case is that when it is not attached to the rest of the LHA, the excited electron doesn’t have anywhere to go. So eventually in that case, the electron will become unexcited and in so doing emit some light. However, since there is energy loss in this system, the emitted light is of a lower energy — so it is redder than the light it absorbed.
Plants look green because of the light absorbing characteristics of chlorophyll. Chlorophyll absorbs red and blue light. The water in the plant leaf is shiny and reflects the rest of the light — green.
Okay, with that background info we can go back to the interesting experiment. You can try this at home, but be very careful because acetone is flamable, and blenders can create sparks. Be sure to have fire extinguisher at the ready and also take note that I take no responsibility for death, blindness or dismemberment that results. On the other hand, I was able to do this experiment successfully with a four year old sister and my mother-in-law.
Take some spinach — or any green leafy plant, grass clippings work too. Put it in the blender with some acetone (nail polish remover works). Blend for a little while until it makes a rich green juice. Now strain out the plant matter and reserve the precious green liquid. If you look through the liquid at a bright light source, you will see the light that is not absorbed by the chlorophyll — green is not absorbed so the liquid looks green.
Now for the really cool part. Look at the liquid when it is lit by a strong light from the side. Sunlight works the best, but light from an overhead projector is okay, too. The chlorophyll absorbs the light and then emits light back out. But it emits a different color! The solution will be a deep ruby red. It is really wild to watch the color change depending on your point of view.