All atoms and molecules have frequency limited absorption and emission spectrum. This is the consequence of dispersion (Kramers-Kronig) relations and its quantum mechanics extension (optical theorem). Theoretical black bodies approximate wavelength-insensitive detectors but their absorption spectrum is far from uniform. The statement that chlorophyll molecule is not sensitive to wavelength is plainly wrong--but organic molecules usually have wide absorption bands. In fact, plants are green because the solar light has a maximum in yellow-green part of the spectrum.

"As shown in detail in the absorption spectra, chlorophyll absorbs light in the red (long wavelength) and the blue(short wavelength) regions of the visible light spectrum.Green light is not absorbed but reflected, making the plant appear green"

https://www.google.nl/imgres?imgurl=http://www.webexhibits.org/causesofcolor/images/content/chloroabs.gif&imgrefurl=http://www.webexhibits.org/causesofcolor/7A.html&h=275&w=315&tbnid=sIaZIA9q0zH0_M:&q=colour+of+chlorophyll+explained&tbnh=160&tbnw=182&usg=AFrqEzeC6daoxtWdCkiyzbLh85ott1XMjQ&vet=12ahUKEwjF787FkvzcAhWDKVAKHS9bA1EQ9QEwAHoECAoQBg..i&docid=vOl9R9_oUIdPwM&sa=X&ved=2ahUKEwjF787FkvzcAhWDKVAKHS9bA1EQ9QEwAHoECAoQBg

I agree with Harry

Actually I am not asking about chlorophyll absorption spectrum. We all know chlorophyll absorbs more photons at blue and red wavelength. The problem I want to ask is after a photon is already absorbed by the chlorophyll, why does the utilization efficiency of that photon still depend on its wavelength? Chlorophyll is excited on a photon basis: once the photon is already absorbed, it will excite one electron from chlorophyll, regardless that that photon is red or blue or even green (or that's what I read). Then shouldn't the quantum yield, which measures the number of photons used per absorbed photons, be the same for every wavelength?

provide the references where you read that the QY is not dependent on lambda

Dear Duy Minh Pham

The wavelengths are different in electron excitation and also in quantum yield. Blue light due to its high energy content causes excitation of electrons to the second orbit (second singlet state), then it releases the extra energy as heat and reach to the first orbit as the red light caused the excitation (fist singlet state). It has been always confirmed that the maximum quantum yield of photosystem II is lower for the red light grown plants than the plants grown under other wavelengths. It has been indicated that red light causes carbohydrate accumulation which result in a feedback inhibition on quantum yield of red light exposed plants.

Give a reference for your statements so that we all can read and study this

QY is generally independent of excitation wavelength. This is called Kasha-Vavilov rule. This is a direct consequence of Kasha's rule.

https://goldbook.iupac.org/html/K/K03371.html

https://nvlpubs.nist.gov/nistpubs/jres/80A/jresv80An3p389_A1b.pdf

Azulene is the most famous exception to this rule. If the quantum yield varies among wavelength it means that there are multiple excited states and efficient competitive channels are present.

I am struggling to understand your question. Do you mean why QY is dependent on emission wavelength? QY is total photons emitted by total photons absorbed. So you cannot just consider certain wavelength. You have to consider entire wavelength (spectrum) so as to cover all the emission photons. If I consider a certain section of the spectrum my result will be highly subjective and of course will contain lots of conditions apply. QY is a property of molecule and its surrounding. It is not dependent on our choice of wavelength or instrument.

I googled for publications myself, now that my question for references was not honoured

Noticed that QY of the fluorescence is low

So the new question for the questioner is which Quantum Yield do you mean

that for Fluorescence or Photochemistry?

see for overview

Chlorophyll fluorescence—a practical guide FREE

Journal of Experimental Botany, Volume 51, Issue 345, 1 April 2000, Pages 659–668,

Dear Harry

In the followings you can find a picture taken from the following book:

Heldt H, Piechulla B, Heldt F. 2011. Plant Biochemistry. Translation of the 4th German edition. Academic Press.

and some more publications showing red light syndrome on photosynthesis:

Trouwborst G, Hogewoning SW, van Kooten O, Harbinson J, van Ieperen W. 2016. Plasticity of photosynthesis after the ‘red light syndrome’in cucumber. Environmental and Experimental Botany 121, 75-82.

Hogewoning SW, Trouwborst G, Maljaars H, Poorter H, van Ieperen W, Harbinson J. 2010. Blue light dose-responses of leaf photosynthesis, morphology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light. Journal of Experimental Botany 61, 3107-3117.

I would be happy to discuss this issue more, since our experiments also confirmed this malfunctioning of photosynthesis by red light.

Kind regards

Sasan

@ Sasan Aliniaeifard

Thank you for your entry

I am reading the 1st pdf

Second pdf: a general Jablonski scheme for the fate of the energy in excited electronic states