text: To stop the electron transfer chain completing, producing output signals, the input of a photon, , is used to produce a pump probe spectroscopy effect by promoting an electron in an electron transfer chain. The fall of the pump probe promoted electron produces an output that is quenched down an electron transfer chain.
  An alternative is similar to the AND gate alternative; an input causes a change in molecule structure breaking the electron transfer chain by not allowing the smooth energy transfer of electrons.