Chlorophyll is involved in capturing energy from light and converting that energy into sugar. It's an integral part of photosynthesis. I don't quite remember anything beyond that off the top of my head. But the answers are there, just open up your bio textbook!
Chlorophyll doesnt split the water "directly", it recieves light energy (hv), gets excited (Chla*) then sends that excited electron into light reaction (which produces energy and reductant) . This is all I remember!