Charge-transfer Transition Energy
The absorption wavelength of charge-transfer bands, i.e., the charge-transfer transition energy, is characteristic of the specific type of donor and acceptor entities.
The electron donating power of a donor molecule is measured by its ionization potential which is the energy required to remove an electron from the highest occupied molecular orbital. The electron accepting power of the electron acceptor is determined by its electron affinity which is the energy released when filling the lowest unoccupied molecular orbital.
The overall energy balance (ΔE) is the energy gained in a spontaneous charge transfer. It is determined by the difference between the acceptor's electron affinity (EA) and the donor's ionization potential (EI), adjusted by the resulting electrostatic attraction (J) between donor and acceptor:
The positioning of the characteristic CT bands in the electromagnetic spectrum is directly related to this energy difference and the balance of resonance contributions of non-bonded and dative states in the resonance equilibrium.
Read more about this topic: Charge-transfer Complex
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