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How do chlorophyll molecules capture light energy?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — photosynthesis Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

Chlorophyll molecules capture light energy by utilizing their structure to absorb photons, which excites electrons within the molecule to higher energy states. This process occurs primarily within light-harvesting antenna complexes, which consist of hundreds of chlorophyll and carotenoid pigments arranged to efficiently absorb light across various wavelengths.123

When a chlorophyll molecule absorbs light, the resulting excitation energy is transferred through the antenna array to a specialized pair of chlorophyll a molecules located in the reaction center. This transfer is crucial because, while the reaction center is essential for converting light into chemical energy, it is not highly effective at absorbing sunlight on its own.23

Once the excitation energy reaches the reaction center, the specialized chlorophyll a molecules (such as $P_{680}$ or $P_{700}$ ) become excited and undergo a charge-transfer reaction. They release an electron to an adjacent acceptor, initiating a series of electron transfers that ultimately convert light energy into stored chemical or electrical energy across the photosynthetic membrane. Excess energy that cannot be utilized is sometimes released as heat or fluorescence.123