1. Chlorophyll-a is an essential photosynthetic pigment as it converts light energy into chemical energy and acts as a reaction centre. 

2. Initially, it lies at ground state or singlet state but when it absorbs or receives photons (solar energy), it gets activated and goes in excited state or excited second singlet state. 

3. In the excited state, chlorophyll-a emits an electron. The emitted electron is energy rich, i.e. has extra amount of energy. 

4. Due to the loss of electron (e_- ), chlorophyll-a becomes positively charged. This is the ionized state. 

5. Chlorophyll-a molecule cannot remain in the ionized state for more than 10‘9 seconds. Hence the photochemical reaction or electron transfer occurs very fast. 

6. The energy rich electron is then transferred through various electron acceptors and donors (carriers). 

7. During the transfer, the electron emits energy which is utilized for the synthesis of ATP. This shows that light energy is converted into chemical energy in the form of ATP.