Archaea are prokaryotes( which means the nucleus has no compartment). It possesses bacteriorhodopsin which has functions unrelated to phosynthesis. The bacteriorhodopsin helps to absorb energy for the movement of ions across the cell membranes.
Bacteria is also a prokaryote and its pigment is called proteorhodopsin and its functions are also unrelated to phosynthesis. It helps in active transport of ions.
Bacteriorhodopsin is a protein used by Archaea, most notably by halobacteria, a class of the Euryarchaeota. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell
Bacteriorhodopsin is an integral membrane protein usually found in two-dimensional crystalline patches known as "purple membrane", which can occupy up to nearly 50% of the surface area of the archaeal cell.
Proteorhodopsin also known as pRhodopsinbis a family of over 50 photoactive retinylidene proteins, a larger family of transmembrane proteins that use retinal as a chromophore for light-mediated functionality, in this case, a proton pump
