Linker molecules aromatic linkers

Pyrenes appear to be once again amongst the most useful linkers, and the attachment of metal-complexed porphyrins has already been discussed in the section on small aromatic molecules. Porphyrin rings bearing a metal center can also be directly adsorbed on the CNTs sidewalls, and they have been shown to exhibit an increased charge transfer from the metal to the tubes, presumably mediated by the aromatic moieties [100]. A similar behavior is exhibited by the phthalocyanine-based complexes [101]. Other aromatic molecules can be used for appendages, including triphenylphos-... 

Figure 138 DFDNB is a small cross-linker able to form covalent bonds between amine-containing molecules. The aromatic fluorine atoms are readily displaced by nucleophiles.

While the detection of the Si-H and Si-C modes indicates HREELS can probe the buried molecule/silicon interface, in general this method will be most sensitive to the terminal groups at the vacuum/monolayer interface. This is illustrated in Fig. 9 where spectra for several modified surfaces with different terminal functionalities are shown. In each case this terminal group is tethered to the surface via a Cio alkyl linker yet the spectra are significantly different. This is particularly evident in the spectra for the thienyl terminated surface in which the aromatic C-H stretch is clearly observed. In contrast this mode is quite small in the FTIR spectra, which are dominated by the contributions of the alkyl linker chain [51]. The observation of strong terminal group modes in the HREELS spectra indicates that these functional groups are likely present at the surface of the film and not buried back towards the H-terminated surface. This is consistent with their availability for sequential reactions as discussed in the previous section. 

In CHEC-II(1996) the detailed discussion of thiophenes as intermediates was, somewhat arbitrarily, limited to photochemical and electrocyclic processes. Additionally, reactions were included which destroy the aromatic thiophene skeleton to give rise to open chain molecules. In this scheme very recent applications of thiophenes such as thiophene-based amide linkers in solid-phase synthesis <2006JOC6734> or V-(2-thienyl)sulfonyl aldimins in chiral Mannich reactions <2006OL2977> did not be fit in. 

In 1990, Osuka, Maruyama, Mataga, and coworkers examined porphyrin dyad 4 and other molecules closely related to dyad 3 with different aromatic linkers joining the macrocycles [19], When the zinc porphyrin of 4 was excited in dimethylforma-mide solution, Pzn-PFe(m) was produced. It decayed with a time constant of 52 ps, and the Pzn -PFe ii) state was observed by transient absorption techniques. The charge-shifted state decayed in 1.6 ns. By studying photoinduced electron transfer in the entire series of molecules with different linkages, the dependence of rate constant on the separation of the porphyrins was determined. A value for f in Eq. 2 of 0.4A- was obtained. 

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