The Nobel Prize in Chemistry 1915 was awarded to Richard Willstätter "for his researches on plant pigments, especially Chlorophyll".
 

Chlorophyll is part of the engine that drives photosynthesis, possibly the most important reaction on earth, in which light is absorbed from the sun and converted into chemical energy to fuel the growth of plants. Our understanding of the chemistry of chlorophyll owes much to Richard Willstätter's extensive investigations of the structures of natural pigments. Willstätter was the first to provide conclusive evidence for the chemical relationship between chlorophyll and a vital component for life in animals — the red oxygen-carrying pigment in blood called haem. He showed that chlorophyll shares a similar structure to haem, with its essential chemical element magnesium held tightly within the heart of a chlorophyll molecule in the same way in which iron is held within haem.