What is photolysis and mention its importance in photosynthesis?

Photolysis is any reaction where a chemical compound splited by photon (units of light). In a lay man's language splitting up a chemical compound in presence of light. In photosynthesis photons split water molecule into its constituents and release energy in the form of electrons which are transported to the electron transport chain along electopotential gradient

The reaction is a s follows

H2A + 2 photons (light) 2e- + 2H+ + A

A can be oxygen or in purple sulfur or cyanobacteria can be S