Quantum donor-bridge-acceptor

In conclusion, quantum mechanical calculations disclose the donor-bridge-acceptor character of the exTTF-oPPE -C60 systems and suggest that the HOMO -> LUMO transition would represent a nearly complete charge-transfer... 

Interestingly, inverted behavior has been observed for reactions in solution between donors and acceptors that are not attached by molecular bridges. In a novel approach, the diffusion-control problem was avoided by monitoring charge recombination in geminate radical pairs (see Fig. 3). It is possible to extract the CR rate constant, k , from the quantum yield of radicals escaping from the geminate radical pair (Eq. 4), where is monitored with a cation radical trap such as dimethoxystilbene (DMS). 

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. 

The pioneering work Forster and Hoffmann [28] on the viscosity dependence of the fluorescence quantum yield of triphenylmethane dyes (TPM) has set the foundation for several reports in these dyes (Fig. 12). It was found that both an ability to twist around the carbocationic center and the donor-acceptor properties are important [66], Specifically, a strong intramolecular quenching is observed for 34 that is virtually absent (two orders of magnitude slower quenching rate) in the bridged... 

---