Chlorophyll and the Photoelectric Effect
I have been trying to put together a lesson on the photoelectric effect applied to biology and chemistry concepts, and have been unable to find an explanation for some things. Here is some background:
When chlorophyll is extracted from a green plant (say, with acetone) the resulting solution will fluoresce bright red when exposed to UV light. I gather that the magnesium atom in the center of chlorophyll's porphyrin ring captures the UV photon and excites an electron via the photoelectric effect, and in the presence of the cytochrome complex will donate the excited electron into the ETC. This explains why ordinary leaves do not fluoresce, but ground up leaves - in which some the chloroplasts have been ruptured - will fluoresce.
#1) Obviously, red is a lower energy photon than UV, so where does that missing energy go? Is there first an emission of a slightly lower-energy UV, followed by a red? That's the only thing I can think of to explain the rather large amount of missing energy.
Or maybe the energy of the red photons corresponds to the excess energy that the excited electron would have had if it had been transferred to photosystem II?
#2) Why red? It stands to reason that specific red color corresponds to the active wavelength of P680, the pigment present in photosystem II, but I have no basis for why that is, or how it occurs. Which I suppose makes this a corollary to question #1, specifically HOW that particular color is emitted.
I realize that (a) my knowledge is patchy at best and therefore likely to be wrong, and (b) a suitable answer would be very long. Any help and/or references would be appreciated. Thanks