Chlorophyll is a green pigment that helps absorbing sunlight for photosynthesis. Its molecule is made of a magnesium atom in a porphyrin ring. There are two main types of chlorophyll, a and b and they are differentiated by their composition of a side chain. Chlorophyll a has -CH3 while b has a CHO side chain.
Chlorophyll a absorbs the wavelengths of violet-blue and orange-red light and functions as a primary electron donor during the election transport chain in photosynthesis. It also functions in transporting energy to the reaction center where P680 and P700 are located.
Its green color which also makes the leaves appear green is caused by its specific range of absorbed light. The violet-blue and red-orange wavelengths are absorbed while the green wavelength is reflected. Therefore the trees, especially in the summer when chlorophyll is most active appear green.