In photosynthesis the energy transfer involves the direct excitation of carotenoids by light to form the first excited singlet state, and the subsequent transfer of this excitation energy to chlorophyll to initiate the process of photosynthesis. This type of process can effectively extend the wavelength of light available to an organism for photosynthesis.
Carotenoids also play a major role in the photoprotection of cells and tissues.
This ability is the result of energy transfer reactions in which the energy of triplet state sensitizers or singlet oxygen is transferred to carotenoid molecules in the ground state, forming triplet state carotenoid molecules. The energy acquired by the carotenoids is then lost as heat and the ground state carotenoid is regenerated to undergo another cycle of photoprotection. In Western countries the supply of vitamin A is not critical but in countries of the third world it is still a severe problem. It was shown that the molecular actions occur via up-regulation of the connexin43 gene, the gene responsible for the production of one of the important components of the gap junction. Based on epidemiological data it can be assumed that diets rich in carotenoid-containing fruits and vegetables are associated with significantly decreased risks for a variety of degenerative diseases.