Talk about the excitation of chlorophyll.

When the chlorophyll molecules (or other pigmented molecules) absorb a photon of light, an electron is excited and passes from one layer to another, more distant from the atom nucleus. The excited electron therefore has more energy. This excited state is unstable and the molecule returns to its initial state. In the thylakoid membranes of chloroplasts, there are electron acceptors that receive the excited electrons.