First reaction in photosynthesis:
a. Photolysis of water
b. Excitation of chlorophyll molecules
B)Excitation of chlorophyll molecules
Photolysis is When the electrons excited and leave the chlorophyll molecules, it leaves behind a 'hole.' This electron hole is filled in by a water molecule that is oxidized, or loses electrons, as it essentially splits into two hydrogen atoms, or protons, and an oxygen atom.
So photolysis happens due to the excitation of chlorophyll molecules.