Weakly coupled chromophores

If a molecule consists of several weakly coupled chromophores it may be advantageous to speak of intramolecular CT transitions. The MIM method for calculating the absorption spectra of complex molecules, which has been mentioned in the discussion of substituent effects in Section 2.4.2, is based on this idea. 

The review is restricted to systems that at the most show weak coupling between the two chromophores. It furthermore does not include a discussion on the di-ir-methane type rearrangements. 

By contrast, the bath is composed of modes 2, 3, 4, and 6 which are weakly coupled to the CH stretch. Their fundamental energies are equal to 2,162, 1,007, 2,248 and 1,037 cm 1, respectively. The W(chromophore-bath) and W(bath) operators have been estimated (95) empirically in order to reproduce the Gray and Robiette spectroscopic Hamiltonian (99,101). Finally, the Hamiltonian used in this study can be written (91,95)... 

These noncovalent interactions introduce geometric restrictions that most probably affect the k values. Ground state absorption properties show that the chromophores are weakly coupled when compared to reference monomers comprised of the bridge-substituted donor or acceptor. Highly efficient ET rates, ranging from 70 to 13 ps have been observed for ET from the zinc donor to the free base acceptor. Almost no competition with hole transfer, due to excitation of the free base, was observed, except for dyad 35 in Figure 13.28. Excited state lifetimes for the individual chromophores and ET quantum yields are given in Table 13.3. 

From them we obtain the distribution localization indices L by merely squaring the corresponding coordinates in the above eigenvectors. The results become more clear for very weakly coupled fragments (chromophores) when 1, and we... 

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