.. _sphx_glr_api_gallery_photochem_energy_transfer:

Energy transfer
-----------------

Excitation energy transfer between a donor and an acceptor: Förster
dipole-dipole transfer and Dexter exchange transfer.


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    <div class="sphx-glr-thumbcontainer" tooltip="Förster (1948) showed that an excited donor can hand its energy to a nearby acceptor through dipole-dipole coupling at a rate k_T=\tau_D^{-1}(R_0/r)^6, so the transfer efficiency E=1/(1+(r/R_0)^6) falls from nearly 1 to nearly 0 over a narrow range around the Förster distance R_0 (~chemistrykit.photochem.forster_radius, forster_efficiency). That steepness is why FRET works as a &quot;spectroscopic ruler&quot; for distances of 1-10 nm.">

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  .. image:: /api/gallery/photochem/energy_transfer/images/thumb/sphx_glr_plot_01_forster_fret_efficiency_thumb.png
    :alt:

  :doc:`/api/gallery/photochem/energy_transfer/plot_01_forster_fret_efficiency`

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      <div class="sphx-glr-thumbnail-title">Förster resonance energy transfer: the inverse-sixth-power distance law</div>
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    <div class="sphx-glr-thumbcontainer" tooltip="Dexter (1953) described a second energy-transfer mechanism in which the donor and acceptor swap electrons, which needs their orbitals to overlap. Its rate, k_{ET}=KJ\exp(-2r/L) (~chemistrykit.photochem.dexter_rate), therefore dies off exponentially within a few Å of contact, and because electron exchange conserves total spin it can move triplet energy (triplet sensitization), which dipole-dipole Förster coupling cannot. The log-scale plot shows the straight line of an exponential law, with the slope set by L.">

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  .. image:: /api/gallery/photochem/energy_transfer/images/thumb/sphx_glr_plot_02_dexter_exchange_transfer_thumb.png
    :alt:

  :doc:`/api/gallery/photochem/energy_transfer/plot_02_dexter_exchange_transfer`

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      <div class="sphx-glr-thumbnail-title">Dexter exchange energy transfer: exponential fall-off with distance</div>
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.. toctree::
   :hidden:

   /api/gallery/photochem/energy_transfer/plot_01_forster_fret_efficiency
   /api/gallery/photochem/energy_transfer/plot_02_dexter_exchange_transfer