Chlorophyll
The function of the reaction center chlorophyll is to use the energy transferred to it from the other chlorophyll pigments to undergo a specific redox reaction. In this reaction the chlorophyll gives an electron to an electron transport chain. This reaction is how photosynthetic organisms such as plants produce O2 gas, and is the source for practically all the O2 in Earth's atmosphere. Photosystem I typically works in series with Photosystem II.