ZnTPP moiety

Photoelectron transfer from the excited singlet state of zinc(II) tetraphenylpor-phyrin (ZnTPP) to MV " in a compartmentalised system in which the ZnTPP moieties are covalently attached to amphiphilic sodium polysulfonates carrying lauryl 2-(naphthyl)methyl, or cyclododecyl groups, is reported to be much slower... 

Ceo acceptors have not been covered in this chapter, the properties of the dyads 128 and 129 are comparable to those of similar species for which many examples have been reported . However, the corresponding data have been incorporated in Table 13.9 to clearly show that, in dichlorobenzene, the triads display charge separation processes that are strongly enhanced in comparison to those of the dyads 128 and 129. No evidence for eT occurring from the ZnTPP moiety was found by the authors. In addition to these data, a charge recombination rate of 5.0 X 10 s was determined for the triads. In benzonitrile, an intermolecular electron transfer takes place between the triplet state of ZnTPP and the triplet state of Ceo. 

Zinc(II) tetraphenylporphyrin (ZnTPP) can be covalently incorporated into the unimer micelle by terpolymerization using a ZnTPP-substituted acrylamide monomer Zinc(Il) S(4-acrylamidophenyl)-10,15,2(ftriphenylporphynate (ZnAATPP) (Chart 4) (56). The ZnTPP units compartmentalized within the hi er-order unimer micelle are protected from the bulk aqueous phase. Because the amount of the ZnTPP units incorporated in the terpolymers are very small (0.1-0.2 mol %), each ZnTPP unit is independently compartmentalized in the hydrophobic microdomain and is prohibited from encountering otheiB. In the reference copolymer (Chart 4), on the other hand, the ZnTPP moieties are exposed to the aqueous phase. 

Figure 14 Conceptual illustration of compartmentalization of ZnTPP moieties in...

The interesting dual behaviour of porphyrin derivatives is demonstrated by intramolecular electron transfer between an electron-rich tris(4-methylphenyl)porphyrin zinc complex (ZnTPP) and an electron-deficient tris(4-methylphenyl)octafluoroporphyrin (TPOFP) (Teflon porphyrin) free base connected via an azobenzene moiety (438 Scheme 6.209).1250 Upon photolysis at >440 nm, E —> Z photoisomerization (Section 6.4.1) occurs. (Z)-438 can revert to ( )-438 only thermally, because the excited state of the Z-isomer is efficiently quenched by intramolecular electron transfer from ZnTPP to TPOFP, whereas no such interaction is possible in the -isomer because the chromophores are too remote. This approach has been suggested for photocontrolled molecular electronics. 

Other important feature of triarylamine-zinc porphyrin dendrimers is the intramolecular energy transfer from the triarylamine moieties to the zinc porphyrin unit. Interestingly, zinc porphyrin fluorescence emission takes place with higher quantum yield upon excitation in the triarylamine moieties UV absorption bands than upon direct excitation of the ZnTPP unit. Similar antenna effect has been previously reported for a series of carbazole-porphyrin dendrimers [132] encompassing up to 21 redox centers. Their electrochemical pattern is strongly dependent on the way the carbazole are structured along the dendrimer branches and connected to the porphyrin core. 

The design of a system for photoswitching on and off coordination sites in a self-assembled mono-layer (SAM) containing an azopyridine unit has recently been reported by Cook and co-workers. The required SAM was prepared by depositing an unsymmetrical disulfide 28 having 4-(arylazo)pyridine and phenoxy moieties onto an 8-nm-thick film of gold supported on a quartz glass slide. Scheme 64 outlines the system for the evanescent field-driven SAM photoswitch. Zinc tetraphenylporphyrin (ZnTPP) was... 

Fluorescence of the reference copolymer poly(A/ZnTPP) is quenched by PMPS the Stern-Volmer quenching constant (Ks ) is also listed in Table 4. With the terpolymers, however, little or no fluorescence quenching occurs even at a high concentration of PMPS (10 mM). From these results, it is evident that ET from the singlet-excited ZnTPP to PMPS can occur only when the porphyrin moieties are exposed to the aqueous phase and that the singlet ET is prohibited when they are compartmentalized in the unimer micelle. 

---