Fig. 1
The molecular structures (left and right) and energy levels (ground state-binding and excited state-unbinding orbitals (labelled by asterisks), in the middle) of chlorophyll-a and bacteriochlorophyll-a molecules. Arrows indicate the electronic transitions between the highest occupied and lowest unoccupied molecular orbitals, HOMO and LUMO, respectively. The basic differences between the two molecular structures are indicated by red characters