Porphyrin-fullerene

Fullerenes such as C60 are excellent electron acceptors. In a fullerene-porphyrin-based dyad, the photoexcited state of the Qo accepts an electron from the linked zinc porphyrin group to give a charge-separated state. 

The Fullerenes form particularly strong complexes with porphyrins as exemplified by the X-ray crystal structure of the covalent Fullerene-porphyrin conjugate 15.8 (Figure 15.29).48 This property allows fullerenes and porphyrins to form extended supramolecular arrays (even when not covalently linked) and has been used to engineer host-guest complexes in which a Fullerene is sandwiched in between a pair of porphyrins, and ordered arrays involving interleaved porphyrins and Fullerenes. Applications include the use of porphyrin solid phases in the chromatographic separation of Fullerenes and potential applications in porous frameworks and photovoltaic devices.49... 

Some representative examples of fullerene-porphyrin dyads are shown in Scheme 9. In other examples, porphyrin analogs such as phthalocyanines and subphthalocyanines have been used for the construction of efficient dyads. Again, the most straightforward approach for their synthesis involved 1,3-dipolar cycloaddition of the appropriate azomethine ylides to C60 [203-205]. Also, with the aid of the Bingel reaction, other phthalocyanine-fullerene systems have been prepared [206,207] with the most prominent example being the one that contains a flexible linker possessing an azacrown subunit [208]. The novelty of this dyad can be found in the nature of the linker that could, in principle, induce conformational changes in the multicomponent system when certain ions (e.g., alkaline ions) are present. As a direct consequence this would potentially allow an external control over the electronic interactions between the phthalocyanine and fullerene units. 

Computational studies followed by molecular modeling were performed on a variety of fullerene-porphyrin dyads that contained either flexible polyether or rigid steroid linkers as well as on doubly linked cyclophane-like C60-porphyrin [212]. Not surprisingly those studies confirmed that the attractive van der Waals interactions between porphyrin and C60 units cause these dyads to adopt unusual conformations in order to get together in close proximity. 

In a supramolecular approach to fullerene-porphyrin hybrids, the assembly of a rigidly connected dyad, in which a zinc tetraphenylporphyrin, Zn(TPP), is noncovalently linked to a C60 derivative via axial pyridine coordination to the metal, was reported [219-222]. Photo excitation of the dyad Zn-complex led to electron transfer with very long lifetimes of the charge-separated pairs, as revealed by optical spectroscopy and confirmed by time-resolved electron paramagnetic resonance spectroscopy. Accordingly, two different solvent-dependent pathways can be considered for the electron-transfer processes. Either the excitation of the porphyrin chromophore is followed by fast intramolecular electron transfer inside the complex, or alternatively the free porphyrin is excited undergoing intermolecular electron transfer when the acceptor molecules ap-... 

El-Khouly ME, Ito O, Smith PM, D Souza F. Intermolecular and supramolecular photoinduced electron transfer processes of fullerene-porphyrin/phthalocyanine systems. J Photochem Photobiol C Photochem Rev 2004 5 79-104. 

Starting from the fullerene-porphyrin dyad 63, dendrimers 64 and 65 (generations 1 and 2) were obtained adding five dendritic branches to the remaining octahedral positions of Ceo [133]. The 7t-system of fullerene is disrupted by the... 

Fullerene-porphyrin architectures as photosynthetic antenna and reaction center models 02CSR22. 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

There continues to be an enormous amount of activity in the area of PET, much of it directed towards the development of systems capable of delivering artificial photosynthesis. Many of these systems involve porphyrin units as electron-donors and thus it is appropriate to consider them in this section of the review. A number of new fullerene-porphyrin dyads have been reported. A pyrazolinofullerene (155) has been constructed which facilitates efficient PET when strong donors such as iV,Ar-diethylaniline or ferrocene are linked to the pyrazoline ring. A photosynthetic multi-step ET model (156) based on a triad consisting of a meso,meso- inked porphyrin dimer connected to ferrocene and Ceo as electron-donor and electron-acceptor, respectively, has been synthesized and its ET dynamics (Scheme 38) have been investigated using time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. ... 

Porphyrin-fullerene conjugates attract wide attention for their intramolecular energy and electron transfer properties [87, 88]. By attachment of the porphyrin to two points on the Cgo surface, the interchromophoric spatial relationship in the cyclophane-type molecular dyads trans-2 ( )-52 [67] and trans-1 54 [68] (Scheme 7-8), which controls both energy and electron transfer, is rigorously defined. In the two systems, as well as in the fullerene-porphyrin conjugate 58 [75] (Scheme 7-9), the close proximity between fullerene and porphyrin chromophore leads to a nearly complete quenching of the porphyrin luminescence, presumably as a result of efficient energy transfer between the porphyrin donor and the fullerene acceptor. 

The design of covalently linked donor-fullerene systems capable of undergoing photoinduced electron-transfer processes has been widely studied as a result of the remarkable photophysical [35] and electronic [36] properties of fullerenes. Porphyrins, phthalocyanines, tetrathiafulvalenes, carotenes, and ferrocene [37] have been covalently attached to the fullerene sphere, usually as pyrrolidine[ 60] fullerene derivatives by 1,3-dipolar cycloaddition reactions. 

Fullerene-porphyrin supramolecular discrete host-guest complexes 05ACR235. 

Various fullerenes and C70) were coordinated to zinc(II) and mag-nesium(II) porphyrins via functionalized pyridines or imidazoles (Fig. 7) by D Souza and Ito [10-22]. Both single-point [10,11] and two-point [12-14] binding strategies were employed, together with additional covalent functionalization of the porphyrins with ferrocene (Fc) [10] or boron dipyrrin (BDP) [16]. Similar systems were also studied by Guldi, Diederich, Nieren-garten and Schuster, and the results on the intermolecular and supramolecu-lar photoinduced electron transfer (PET) processes of fullerene-porphyrin and phthalocyanine systems were reviewed recently [23,24]. Since PET is... 

Both porphyrins and fuUerenes can be deposited onto surfaces imder ultra-high vacuum (UHV) conditions as studied by Diederich et aL [126, 127]. In a first step, a monolayer of porphyrins or extended porphyrin analogues can be formed which can be analyzed using AFM or STM imaging techniques. UHV deposition of a second layer of Ceo on top of a full monolayer of porphyrins leads to the formation of supramolecular assem-bhes, and the precise structure of the arrangement of the Ceo on the patterned layer can be controlled by the porphyrin structure. The observed modes of self-assembly result from a delicate balance between the fullerene-porphyrin interaction and the conformational motion within the porphyrin monolayer. 

Optical limiting properties of fullerenes, porphyrins and phthalocyanines have attracted much attention because they have applications in passive solid-state sensors and the human eye protection from high-intensity visible light sources. ... 

Naturally, film formation from fullerene-porphyrin dyads is attractive for photocurrent generation. The group of Sereno has reported the use of dyad 173 (Figure 13.92) in the spin-coating preparation of Sn02-supported films. Using this dyad, in which the distance separating the donor and the acceptor is estimated at 14 A, photocurrent quantum yields of 20% are observed in the presence of hydroquinone as a sacrificial donor. 

Guldi, D.M. (2002). Fullerene-porphyrin architectures photosynthetic antenna and reaction center dyads. Chem. Soc. Rev. 31(1), 22-36. 

D.M., Guldi, I. Zilbermann, G.A. Anderson, K. Kordatos, M. Prato, R. Tafuro, and L. Valli (2004). Langmuir-Blodgett and layer-by-layer fihns of photoactive fullerene-porphyrin dyads. J. Mater. Chem. 14(3), 303-309. 

Sun D, Tham FS, Reed CA, Chaker L, Boyd PD (2002) Supramolecular fullerene-porphyrin chemistry, fullerene complexation by metalated Jaws Porphyrin Hosts. J Am Chem Soc 124(23) 6604-6612... 

Figure 15 (a) A fullerene/porphyrin dyad assembled on the ITO electrodes and (b) a fullerene/porphyrin/ferrocene triad coassembled with BODIPY dye on the gold electrode. 

Photoelectrochemical solar cells based on the fullerene/porphyrin clusters... 

Another approach to design fullerene/porphyrin architectures utilized peptide scaffolds with pendant porphyrin units. These molecular architectures were found to be suitable for complex formation with Cco fullerene molecules. The resulting porphyrin peptide/fullerene composites showed advanced photovoltaic performances with EQEs approaching 56%. The devices also demonstrated broad photoresponse extending into the near infrared region (up to 1000 nm). 

The fullerene-porphyrin composite has been tested as catalysts in the H2 evolution reaction in a five-component system showing a good activity with a turnover number of 73. 

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