Zinc porphyrins arrays

Based on the predominant excitation of the ZnP moiety (>99%) in Ec (ZnP)3 Ceo, the total quantum yield for formation of the final CS state (Fc —(ZnP)3—Ceo ) was determined as 0.83 by applying the comparative method from the nanosecond time-resolved transient spectra due to the CS state (48). The large quantum yield as compared with the value for Fc ZnP—ZnP Ceo (0.34) (47) results from the efficient hole transfer along the meso, meso-hnked zinc porphyrin arrays as compared with that in Fc ZnP ZnP Ceo. The lifetime of the... 

Other supramolecular structures such as dendrimers have also been synthesized with zinc-containing porphyrins. Sixteen free base and sixteen zinc porphyrin units were added at the fifth generation of dendritic poly(L-lysine) and intramolecular fluorescence energy transfer was observed.823 Assembly of supramolecular arrays in the solid state has been achieved with the incorporation of an amide group for hydrogen bonding. Zinc meso-tetra(4-amidophenyl)porphyrin... 

This is in contrast to the results obtained following selective excitation of the PH2 unit discussed above, and yielding a multi-step electron transfer leading to charge separation. The different outcome can be discussed on the basis of the overlap of the HOMO and LUMO orbitals involved in the electron transfer reaction for the Ir acceptor unit and the PH2 donor unit, with the aid of semi-empirical calculations [48]. Remarkably, the zinc porphyrin based array PZn-Ir-PAu, 254+, displays an efficient electron transfer with the formation of a CS state with unitary yield also upon excitation of the iridium complex. This happens because the selective excitation of the zinc porphyrin chromophore discussed above, and the deactivation of the excited state PZn-3Ir- PAu, follow the same paths as those reported in Scheme 8. 

Controversial results have been deduced from the researches of different groups on the sensitization behavior of porphyrin arrays as mentioned above. Some of them revealed that porphyrin arrays have advantages over porphyrin monomers in the sensitization of wide band gap semiconductor while the rest showed the opposite results. The porphyrin dimer composed of a metal free porphyrin and a zinc porphyrin seems the most successful porphyrin array sensitizer so far. Programing the photoinduced energy and electron-transfer sequence in a porphyrin array is the key step toward a good porphyrin array sensitizer. 

Figure 12.7 Various architectures of the porphyrin arrays for light harvesting, (a) Cyclic array with peripheral acceptor (b) cyclic array with integral acceptor (c) tri-branched array with central acceptor (d) starburst array with central acceptor. FB denotes the free base porphyrin and Zn the zinc-porphyrin complex. (Adapted from Van Patten et al. [71])...

Figure 7.13 Zinc porphyrin-containing assembled array formed using tris(pyridylaceto-acetato)aluminium(IIJ) as a template ...

Star-shaped multi-porphyrin arrays have been constructed to mimic energy funneUng in photosynthesis. These dendrimers contain free-base porphyrin cores (Pfb) connected to four dendrons consisting of 1,3, or 7 zinc-metallated porphyrins (Pzn) embedded in an organic matrix coimected by ether linkages (Scheme 21) [70,71]. The periphery consists of methoxy-terminated poly(aryl ether) dendrons. For comparison, cone-shaped arrays consisting of Pfb cores monosubstituted with Pz dendrons were also synthesized. 

Uttiyh S, Pratontep S, Bhanthumnavin W, Buntem R, Kerdcharoen T (2008) Volatile organic compound sensor array based on zinc phthalocyanine and zinc porphyrin thin films. In 2nd IEEE International Nanoelectronics Conference, 2008. pp 618-623... 

In a series of flexible zinc(II) bis-porphyrins sharing the same linker but differing in the substitution pattern (ortho, meta and para in the meso-phenyl group), the self-assembled porphyrin arrays with DABCO show different structures as shown in Fig. 13 [34]. A detailed analysis using UV-vis... 

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