Charge-transfer transition energy

Ligand Field and Charge-Transfer Transition-Energies for M(Nj)s... 

Fig. 2 Mulliken correlation of the ionization potentials (IP) of various enol silyl ethers with the charge-transfer transition energies (/jvct) of their EDA complexes with chloranil. Reproduced with permission from Ref. 36.

Stable pyridinyl radicals were discovered while establishing the linear relationship between the lowrat charge-transfer transition energy for 1-alkylpyridinium iodides (Eq. 1) and the one-electron reduction potentials of 1-alkylpyridinium ions... 

Figure 1. Mulliken correlation of the charge-transfer transition energy ( cr = hvci) with the ionization potential [IP) of ferrocene and arene donors in 6w(durene)iron(II) complexes. The straight line is arbitrarily drawn with a slope of unity [124].

Figure 2. Variation of the charge-transfer transition energy ( cr) with the reduction potential ( °red) of pyridinium acceptors in CT ion pairs with TpMo(CO)3 as the donor [127].

It has long been realized that excellent correlations exist between 1/2 or and molecular orbital parameters [172,178-181]. Correlations between voltammetric data and experimental observables such as ionization potentials (IP) [172,178,182,183], charge-transfer transition energies [172], and positions of p-bands in ultraviolet (UV) absorption spectra of the hydrocarbons [4,172] have been reported as well. The basis and limitations of such correlations have been examined critically [147,175,184]. For alkyl aromatic hydrocarbons (AAHs), the slope, a, of the correlation line [Eq. (56)], where E° is the standard potential for the reversible one-electron oxidation, is close to unity and has been used to suggest that in MeCN the solvation energies of the hydrocarbon radical cations are constant throughout the series [175]. 

Frontier orbital mapping Thus far we have presented systematic relationships which are purely empirical. However, it is instructive to merge these electrochemical and spectroscopic observations into one conceptual framework. We ascribe notional redox potentials (E i/2) to the nitrile acceptor and halide donor, as before, and so express the charge-transfer transition energies as follows. 

For weak complexes the charge-transfer transition energy can be related to the electronic properties of the interacting partners by the following relationships [11,15] ... 

The charge-transfer transition energy and the half band width vary considerably with solvent. 

Another cycle involves spectroscopic measurement of the optical analogue of electron transfer, the charge transfer transition energy, hvd (Figure 1-18). 

The resonance energies and charge-transfer transition energies of P are not directly measurable, and attempts to calculate them on the basis of the crystal structure are subject to major uncertainties. However, the oxidized special pair (P+) should have a series of eigenstates whose separations depend largely on resonance interactions between the two BChls.4,5 We... 

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