Metal complexes play a crucial role in the process of photosynthesis, which is the process by which plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose or other sugars. Photosynthesis can be divided into two stages: the light-dependent reactions and the light-independent reactions also known as the Calvin cycle . Metal complexes are primarily involved in the light-dependent reactions, where they contribute to the conversion of light energy into chemical energy in the form of ATP adenosine triphosphate and NADPH nicotinamide adenine dinucleotide phosphate .There are several metal complexes that are essential for the process of photosynthesis, including chlorophyll, which contains a magnesium ion Mg2+ at its center, and the reaction centers of Photosystem I and Photosystem II, which contain iron-sulfur clusters and manganese ions Mn2+ , respectively. These metal complexes are responsible for the photochemical properties that make them well-suited for photosynthesis.1. Absorption of light energy: Metal complexes, particularly chlorophyll, are responsible for absorbing light energy from the sun. Chlorophyll absorbs light most efficiently in the blue and red regions of the visible spectrum, which is why plants appear green as they reflect green light . The absorbed light energy is used to excite electrons within the metal complex, which initiates the process of photosynthesis.2. Charge separation and electron transfer: The excited electrons in the metal complexes are transferred to nearby electron acceptors, creating a charge separation. This process is facilitated by the metal ions in the reaction centers of Photosystem I and Photosystem II. In Photosystem II, the manganese ions Mn2+ play a crucial role in the water-splitting process, where water molecules are oxidized to produce oxygen, protons, and electrons. The electrons are then transferred to Photosystem I through an electron transport chain, which generates a proton gradient across the thylakoid membrane, ultimately leading to the production of ATP.3. Redox reactions: The metal ions in the metal complexes are involved in redox reactions, which are essential for the conversion of light energy into chemical energy. The iron-sulfur clusters in Photosystem I are responsible for the reduction of NADP+ to NADPH, which is used in the light-independent reactions Calvin cycle to fix carbon dioxide into glucose.In summary, metal complexes play a vital role in the process of photosynthesis by absorbing light energy, facilitating charge separation and electron transfer, and participating in redox reactions. These photochemical properties make certain metal complexes, such as chlorophyll and the metal ions in the reaction centers of Photosystem I and Photosystem II, well-suited for the conversion of light energy into chemical energy.