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Chlorophyll-a (the primary one), chlorophyll-b, and(?) beta-carotene (plus other accessory pigments / carotenoids) dictate which portions of the EM spectrum are used as energy by plants.

Absorption

Actual production

Some additions

Plants only use part of the available spectrum, because of these limitations.

The Sun's output is:

Sun

Obviously, plants are evolved to work in our environment, ie: with stuff the Sun puts out.

Are there any other hypothetical chemical compounds which can transform energy from other portions of the spectrum? Bonus points if they're made from common atoms, instead of rarer, higher elements.

ie: If you had a different star with different output levels (but are there?, I think that the sun is a blackbody radiator, and all of those curves look generally the same??), what types of chemical compounds might you encounter in their ecosystems?

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  • $\begingroup$ I am wondering about waste heat. Would absorbing a wider spectrum make the plant overheat and drop efficiency? Would the drop be bigger than the gain? $\endgroup$
    – Ville Niemi
    Mar 8, 2015 at 11:22
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    $\begingroup$ Bacteriochlorophyll can work. It uses a completely different part of the spectrum. $\endgroup$
    – HDE 226868 ♦
    Mar 8, 2015 at 13:17
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    $\begingroup$ Blackbody curves generally have the same shape, but the frequency peak shifts quite dramatically with temperature. You could go all the way into the blue spectra, and thus require plant pigments to match. $\endgroup$
    – Mike L.
    Mar 8, 2015 at 16:37
  • $\begingroup$ While the outputs of stars may change a little (ask that at Astronomy.SE), the absorption spectrum of the atmosphere varies with its composition a whole lot. $\endgroup$
    – SF.
    Mar 11, 2015 at 13:38

2 Answers 2

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Edit2 Finally getting the artificial/hypothetical part is what you actually asked for I dug deeper into this.

Artificial Photosynthesis

Current research

There is research on Artificial Photosynthesis dealing with what potential substances could be used to create a photosystem.

The photosensitizers commonly used in artificial photosynthesis are mainly metal-containing complexes including platinum, rhodium, iridium and most often ruthenium as ruthenium polypyridine complexes.

Organic complexes successfully used as photosensitizers are eosin Y and rose bengal.

Hypothetical Photosystems

The part of the photosystem determining what wavelengths can be used for photosynthesis is the Light-harvesting complex.

And now to answer your original question

Are there any other hypothetical chemical compounds which can transform energy from other portions of the spectrum?

Yes there are. A lot.

Absorption of a photon by a molecule can lead to electronic excitation when the energy of the captured photon matches that of an electronic transition.

So basically, any molecule capable of absorbing photons / electromagnetic radiation – be it visible light or something else – could be used to harvest light / radiation.

Natural Photosynthesis in plants

plus other accessory pigments / carotenoids

Just to add some accessory pigments for reference:

Name | absorption maximum

  • Chlorophyll c | 500-600nm
  • Chlorophyll d | 710nm
  • Chlorophyll f | 720nm

Natural Photosynthesis in other organisms

Purple bacteria

As has been mentioned in the comments there is also bacteriochlorophyll which is found in purple bacteria.

Name | absorption maxima

  • Bacteriochlorophyll a | 805, 830-890
  • Bacteriochlorophyll b | 835-850, 1020-1040
  • Bacteriochlorophyll c | 745-755
  • Bacteriochlorophyll cs| 740
  • Bacteriochlorophyll d | 705-740
  • Bacteriochlorophyll e | 719-726
  • Bacteriochlorophyll f | 700-710
  • Bacteriochlorophyll g | 670, 788

Cyanobacteria, red algae and glaucophytes

The phycobilisomes found in these organisms can harvest light between 500 and 650nm depending on their structure.

And to give you an idea of what scientist think is possible in terms of naturally occurring photosynthesis / photosynthetic pigments on earth checkout http://sydney.edu.au/news/84.html?newsstoryid=5463. Quote from the article:

"Discovering this new chlorophyll has completely overturned the traditional notion that photosynthesis needs high energy light," Dr Chen said.

"It is amazing that this new molecule, with a simple change to its chemical structure, can absorb extremely low energy light. This means that photosynthetic organisms can utilize a much larger portion of the solar spectrum than we previously thought and that the efficiency of photosynthesis is much greater than we ever imagined.

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  • $\begingroup$ Since this is running off of heat/infrared wavelengths... what output does the human body have? ie: could we run our own oxygen-plant re-breathers? $\endgroup$
    – user3082
    Mar 9, 2015 at 22:57
  • $\begingroup$ This 'different approach' was what I was trying to ask about in my question. :) $\endgroup$
    – user3082
    Mar 10, 2015 at 9:00
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Already exists, During autumn, temperate plants sacrifice chlorophyll to produce different pigments. These pigments take advantage of the inferior intensity autumn/winter sun.

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    $\begingroup$ Answers here are expected to be clear authoritative, self contained and explain why they are correct. In future please write more than two short sentences. You could put some effort in and tell us about xanthaphyll and what wavelengths it absorbs and its relative efficiency, or cholecalceferol - the fact that it's nearly 2000% more energy efficient in the electron transport chain. $\endgroup$
    – Jiminy Cricket.
    May 12, 2020 at 12:30

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