The term chlorophyll derives from the Greek words χλωρός (chloros - "green") and φύλλον (phyllon - "leaf"). The basis of chlorophyll is a macrocycle containing four pyrrole rings and Mg²⁺ ion in the centre. The side chains contain hydrocarbon radicals of various lengths and saturations, and oxygen-containing functional groups. There are 5 types of chlorophyll - a, b, c1, c2, d, they differ in the type of side chains. The plants contain only chlorophyll a and b, which have a long hydrocarbon wick-type chain.

Chlorophyll contains a fully conjugated tetrapyrrole system (18 -electrons), and therefore absorbs light in the visible range. The absorption maximum of chlorophyll a is in the the blue and yellow spectra of light. The combination of these colours results in the typical green colour of fresh leaves.

Chlorophyll is the main structural unit of photosynthetic light-trapping devices (antennae) of green plants, which are nanosized supramolecular complexes containing up to several hundred pigments from the protein environment. The main function of chlorophyll is to absorb light, transform the light energy into electronic one and pass it to neighbouring molecules by van der Waals (dipole-dipole) interactions. The chain of chlorophyll transmits electron energy to the photosynthetic reaction centre, where it is used for charge separation and subsequent redox reactions. Chlorophylls are also contained in the reaction centres of green plants, where they play the role of the primary electron donor.

In plants, chlorophylls are located in photosynthetic membranes as part of the antennae and reaction centres, where spatially they are fixed in certain locations by wick-type side chains and by additional ion complexes formed between Mg²⁺ ion and polypeptide protein chains.

In purple and green bacteria, bacteriochlorophyll perform the functions of chlorophyll; they, unlike chlorophyll, have one or two pyrrole rings partially hydrogenated. Because of this, bacteriochlorophylls absorb light of longer wavelength (and lower energy) than chlorophylls do.