Could Infrared-Loving Chlorophyll Let Solar Cells Capture More Energy?

By Joseph Calamia | August 20, 2010 6:04 pm

stromatolitesAfter mashing up rock and algae chunks known as stromatolites, researchers have found a new type of chlorophyll, the pigment in plants that takes in light and provides energy for photosynthesis. Unlike its known cousins, this chlorophyll uses infrared light–that’s a surprise to some researchers, who doubted that lower frequency infrared had enough energy to split water for photosynthesis’s oxygen-creation.

“Nobody thought that oxygen-generating organisms were capable of using infrared light… ,” says Samuel Beale, a molecular biologist at Brown University whose work centers in part on chlorophylls [but who was not involved with the study]. “I think what they found here is a new modification of chlorophyll that shows the flexibility of photosynthetic organisms to use whatever light is available.” [Scientific American]

Though the paper only appeared yesterday in Science, some researchers already have grand plans for the molecule, called “chlorophyll f.” Because f can harness the energy in lower frequency light (706 nanometer wavelength) and over half of the sun’s light comes in infrared, the newly found chlorophyll might find use in solar cells. Comments Shuguang Zhang:

“It’s like a wider net to catch more fish.” He is currently working with Michael Grätzel of the Swiss Federal Institute of Technology in Lausanne, developer of low-cost dye-sensitised solar cells that use inorganic molecular dyes to absorb light in the same way that chlorophyll does. [New Scientist]

Chlorophyll f joins a previously known family of four: chlorophyll a, b, c, and d. Chlorophyll a is the most popular–appearing in green plants. It absorbs light in the blue (465 nanometer wavelength) and red (665 nanometer wavelength) parts of the spectrum, and reflects the green light we see. The other types each have a shifted spectrum, but even chlorophyll d, absorbing most light around 697 nanometers, doesn’t reach chlorophyll f’s range.

Having the ability to absorb infrared might help the blue-green algae that produced chlorophyll f thrive in its stromatolites habitat, where water, sediment and other organisms may prevent other frequencies of light from reaching the algae.

“In nature this very small modification of the pigment happens, and then the organism can use this unique light,” says molecular biologist Min Chen of the University of Sydney in Australia. Chen and her colleagues identified the new pigment in extracts from ground-up stromatolites, the knobby chunks of rock and algae that can form in shallow waters. The samples were collected in the Hamelin pool in western Australia’s Shark Bay, the world’s most diverse stromatolite trove. [Science News]

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Image: flickr /robertpaulyoung

CATEGORIZED UNDER: Environment, Living World
  • Georg

    It absorbs light in the blue (465 nanometer wavelength) and red (665 nanometer wavelength) parts of the spectrum, and reflects the green light we see.

    It reflects the near infrared as well, a very unique feature compared
    to most other dyes and pigments. (making plants bright in infrared
    night vision gadgets)
    What about reflection in this new chlorophyll?
    But very strange is that gap in the green of the “normal” chlorophylls :
    what is this good for?
    Making use of the green light would be easier than using red or infrared.
    (after You mastered the use of blue_green)
    Georg

  • http://phylogenomics.blogspot.com Jonathan Eisen

    Actually, many of us working on microbes have talked about the possibility that they would photosynthesize using infrared light for many years. We even referred to this as thermosynthesis. So this is not that surprising per se, since microbes can pretty much do anything. But it is cool that they found evidence for it.

  • Georg

    We even referred to this as thermosynthesis.

    This is nonsense! Near infrared correlates to a temperature
    above 1000 °C!
    Regards
    Georg

  • Torbjörn Larsson, OM

    Actually stacking differential wavelength sensitivity solar cells have been done for quite awhile, without developers being aware of the nature doing it.

    But very strange is that gap in the green of the “normal” chlorophylls :
    what is this good for?

    AFAIU plant photosynthesis uses a two photon metabolism to extract energy, one energetic blue photon and the remaining sufficient as red. In this way plants uses infalling light more efficiently.

    thermosynthesis

    Right, but the citation shows that it is the oxygenic metabolism that is surprising. It all depends on how the chlorophyll system extracts energy, doesn’t it?

    IIRC people didn’t think you could utilize less energetic photons in the standard way. It would be interesting to know how it does its trick!

    Near infrared correlates to a temperature above 1000 °C!

    So? The sun surface temperature is way above that, it emits photons in a ~ 6000 K roughly black body distribution. The 465 nm photon is from a ~ 6200 K peak black body emitter, the 697 nm from a ~ 4200 K peak bbe, 706 nm from a ~ 4100 K peak bbe.

    Granted the atmosphere filters many of them out (which is why we see in the more pervasive visible light that the atmospheric windows let in), but there are IR photons left, especially these associated with the visible window. Don’t mistake our adaptations wavelength sensitivity for the actual windowed wavelengths.

    As for how the cells extract the incipient photon energy, well that _is_ the trick. But it isn’t dependent on thermal processes as such, chlorophylls are EM antennas coupled to chemical metabolism. The newly discovered trait should be a phylogenetically related variant of that.

  • Torbjörn Larsson, OM

    EM antennas coupled to chemical metabolism

    Oh, and new research seems to confirm a long held suspicion of some: these natural light absorbers are quantum coupled to the rest of the molecule system. (Because such a model is tested well by predicting the antenna dynamics.)

    Apparently the “Q” coupling [slight pun, since traditional high Q value resonators are good resonators] is both energy and time efficient; instead of EM energy being rattling about and wasted because of bad impedance matching the quantum system moves it without very little loss in energy and time further away to do chemical work.

    IIRC it is a form of quantum coherent container coupling, one can make an analogy of a bath tub sloshing over and the slosh captured timely. In a conventional impedance coupled system the tub would keep sloshing many times from the “back slosh” before settling.

    This speedy coupling releases the antenna quicker and so increases its efficiency in two ways simultaneously.

    Efficient little piece of biochemical machinery function evolution has stumbled on and perfected!

  • Robert E

    Silly question, but if the other four are a, b, c, & d why is the new one f? What happened to e?

  • Chris the Canadian

    For me, what this latest discovery underscores is our need to protect our remaining natural world. It seems we discover 100 new things every day from nature that helps us develop new technologies and medicines. I wonder how many more discoveries have we as a species lost for all eternity because of our gluttonous and wasteful ways. The destruction of rainforests, the polluting of the oceans and air, the melting of arctic and antarctic ice shelves, and the over harvesting and extinction of a variety of animal and plant species are all tragedies.

  • MT-LA

    “…the newly found chlorophyll might find use in solar cells.”
    Is there any current technology that incorporates chlorophyll of any kind into solar cells? Is there something unique to chlorophyll f that would make it easier to incorporate into solar cells? I ask because I think it’s funny that “some researchers already have grand plans for the [newly discovered] molecule” when humanity hasn’t yet learned how to use the more common chlorophyll.

    Torbjörn Larsson, you seem to have a good head for this. Thoughts?

  • Georg

    Is there something unique to chlorophyll f that would make it easier to incorporate into solar cells?

    No, of course not, the last dye to try would be any kind of chlorophyll,
    because it is very sensitive to oxygen and light when isolated from
    living cells.
    Moreover every silicon cell has its optical maximum in the region
    of near infrared. No chlorophyll is needed to achieve that.
    Georg

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