Porphyrins sensitizers

Fukumura, H., Mibuka, N., Eura, S. and Masuhara, H. (1991) Porphyrin-sensitized laser swelling and ablation of polymer films. Appl. Phys. A, 53, 255-259. 

FIG. 4 (a) Latimer diagram of the water soluble zinc tetra-Af-methyl-4-pyridium porphyrin (ZnTMPyP ). (Reprinted with permission from Ref. 47.) (b) Schematic representation of a photosynthetic process based on porphyrin sensitized water-organic interface. Dotted line corresponds to the back electron-transfer process. (Reprinted from Ref. 51 with permission from Elsevier Science.)... 

Despite the potential impact of novel photosynthetic routes based on these developments, the most ambitious application remains in the conversion of solar energy into electricity. Dvorak et al. showed that photocurrent as well as photopotential response can be developed across liquid-liquid junctions during photoinduced ET reactions [157,158]. The first analysis of the output power of a porphyrin-sensitized water-DCE interface has been recently reported [87]. Characteristic photocurrent-photovoltage curves for this junction connected in series to an external load are displayed in Fig. 22. It should be mentioned that negligible photoresponses are observed when only the platinum counterelectrodes are illuminated. Considering irradiation AM 1, solar energy conversions from 0.01 to 0.1% have been estimated, with fill factors around 0.4. The low conversion... 

Figure 3 Type I and type II photooxidation processes with a porphyrin sensitizer illustrated with a modified Jablonski diagram. (S0 = ground singlet state, Si = first excited singlet state, S2 = second excited singlet state, T,i— ground triplet state, Ti = first excited triplet state, i.s.c. — intersystem crossing.)...

Brune, A. Jeong, G. Liddell, P. A. Sotomura, T. Moore, T. A. Moore, A. L. Gust, D. 2004. Porphyrin-sensitized nanoparticulate Ti02 as the photoanode of a hybrid photoelectrochemical biofeul cell. Langmuir 20 8366-8371. 

Nitroimidazoles (such as metronidazole and misonidazole) can enhance the porphyrin sensitized Type I photooxidations83 that is, electron transfer from the sensitizer to the oxygen molecule is facilitated to give more of the superoxide ion (Scheme 6). The Type II mechanism operates by energy transfer from the sensitizer to afford the singlet oxygen84. 

The chemistry of these systems is identical to that already described for 02 and H2 production in homogeneous systems except that MV+ or [Ru(bipy)3]3+ generated during the photochemistry of the bulk solution then regenerate MV2+ or [Ru(bipy)3]2+ by donation or acceptance of an electron at the electrode. Photopotentials of —1.0 V and currents of —1 mA can be generated for long periods in this way. Similar photoelectrical cells using metal phthalocyanine or porphyrin sensitizers have also been developed.359-362... 

Kuroda, Y. Sera, T., Ogoshi, H., (1991) Regioselectivities and stereoselectivities of singlet oxygen generated by cyclodextrin sandwiched porphyrin sensitization. Lipooxygenase-like activity J. Am. Chem. Soc. 113, 2793-2794. 

Keywords Photocurrent Phthalocyanine Porphyrin Sensitizer Solar cell... 

Durrant and co-workers have compared the electron injection and recombination processes of 28 or Zn-28 with that of N3 (a famous ruthenium polypyridyl complex with very high IPCE). Their experiments revealed that the electron injection and recombination kinetic for these three dyes on the surface of Ti02 are almost identical. The high IPCE for N3 dye probably originates from the electron transfer from the iodide redox couple to the dye cations. It is also possible that the lower efficiency of porphyrin sensitizers was caused by the annihilation of the excited states between the neighboring porphyrin molecules because of the closed proximity [70],... 

Porphyrin 37a and 37b have also been employed as sensitizer for a TiC>2 nanotube electrode. For comparison purpose, asymmetrical porphyrin sensitizer with two carboxylic acid groups (38, 39) and 28 have also been tested under identical conditions. The DSSC fabricated from these sensitized Ti02 nanotube presents enhanced charge-collection efficiency respect to the nanoporous Ti02 film built from Ti02 nanoparticles. All the tested five porphyrin sensitizers exhibited efficient sensitization to Ti02 nanotube as revealed by the photocurrent action spectra. 

Another interesting attempt worth noting is the combination of porphyrin sensitized solar cell with a fuel cell made by Moore and Gust. The hybrid cell can realize an open circuit voltage of 1.2 V. The energy conversion efficiency of this photoelectrochemical biofuel cell can, in principle, produce more power than either a photoelectrochemical cell or a biofuel cell working individually [83],... 

Figure 9.10. Schematic diagram of a LiAl-LDH photochemical assembly containing myristate anions, TiOv clusters and Zn-porphyrin. Sensitization of the TiOx by the porphyrin results from the close intralayer proximity of the species. (PVS = propyl violegen sulfonate After Robins and Dutta [120],...

H. Photooxidation of Linoleic Acid by Cyclodextrin-Sandwiched Porphyrin Sensitization... 

Ogoshi and coworkers reported regio- and stereospecific oxidation of linoleic acid by singlet oxygen, which was generated by CDx-sandwiched porphyrin sensitization [125] (Scheme 21). 

Beeby, A., Dickins, R.S., EitzGerald, S., et al. (2000) Porphyrin sensitization of circularly polarised near-lR lanthanide luminescence enhanced emission with nucleic acid binding. Chemical Communications, 1183. 

Tachibana Y., Hague S. A., Mercer I. P., Durrant J. R. and Klug D. R. (2000), Electron injection and recombination in dye-sensitized nanocrystalline titanium dioxide fdms a comparison of ruthenium bipyridyl and porphyrin sensitizer dyes , J. Phys. Ghent. B 104, 1198-1205. 

Scheme 3.13 Photosensitized oxidation of allylic alcohols and cyclohexene with singlet oxygen ( O2) in the presence of a fluorous porphyrin sensitizer (31) [32a].

---