ESOI:The energy separation between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of a molecule or material. It is a measure of how easily an electron can be excited from the HOMO to the LUMO, and therefore how easily a molecule can absorb light. A small HOMO-LUMO gap indicates that a molecule will absorb light at lower energies (longer wavelengths), while a large gap indicates that it will only absorb high-energy light (short wavelengths).
