Chlorophyll



Chlorophyll (also chlorophyl) is a green pigment found in cyanobacteria and the chloroplasts of algae and plants. Its name is derived from the Greek words ("green") and  ("leaf"). Green leafed plants and algaes use chlorophyll to power photosynthesis, the synthesis of complex molecules like sugars from carbon, water, and sunlight. Chlorophyll is a porphyrin, such as heme, a protein cofactor of hemoglobin, the pigment in red blood cells. Chlorophyll is a magnesium porphyrin whereas the heme is an iron porphyrin. Until recently, there were only 4 known types of chlorophyll, termed a, b, c, and d, with most plants producing chlorophyll type a. Chlorophyll type a absorbs blue light (centered on 465 nanometers) and red light (centered on 665 nanometers) but reflects green light allowing leaves to have their green coloring.

Chlorophyll types b and c are much like chlorphyll a. Chlorphyll d is found in certain cyanobacteria and especially absorbs the redder light centered at 697 nanometers. Recently, a new kind of chlorophyll, called chlorophyll f, was found in Australian stromatolites, possibly in a cyanobacteria. This chlorophyll f especially absorbs near infrared light of 706 nanometers.

Some bacteria have pigments that are like chlorophyll, but they aren't used to break water molecules and generate oxygen. Some researchers were surprised that the new chlorophyll was able to provide enough energy to break water molecules into hydrogen and oxygen, since the longer, redder, wavelength means that the light is less energetic.

Photosynthesis
The process of energy conversion begins when a photon excites a chlorophyll molecule, making an electron to move from one molecular orbital to another of higher energy. The excited molecule tends to return quickly to its original, unexcited state. This can happen by converting the extra energy into heat (or a part thereof in fluorescence), by transferring energy to a neighbouring chlorophyll or by transferring the high-energy electron to another nearby molecule the latter two of which are used in photosyntesis