Light is the essential ingredient needed for photosynthesis. The light is absorped by a photoreceptor, which as we have already discussed, in this case is chlorophyll. Chlorophylls are excellent photoreceptors because they contain alternating single and double bonds.
When the light is absorped it excites an electron from its ground energy level to an excited energy level. For most compounds at this point the electron eventually returns to the ground state and the energy is converted to heat. If a suitable electron acceptor is close by, though, the excited electron can move from the initial molecule to the acceptor. Obviously, this then leaves the initial molecule with a positive charge (It has lost an electron) and the acceptor with a negative charge (as it has gained an electron). This process is called Photoinduced Charge Separation. The electron involved can now reduce other species and allow them to store the light energy in chemical forms.
