Porphyrin nanotubes

Wang Z, Medforth CJ, Shelnutt JA (2004) Self-metallization of photocatalytic porphyrin Nanotubes. J. Am. Chem. Soc. 126,16720-16721... 

Murakami H, Nomura T, Nakashima N (2003) Noncovalent porphyrin-functionalized single-walled carbon nanotubes in solution and the formation of porphyrin-nanotube nanoctunpo-sites. Chem Phys Lett 378 481-485... 

Applications of porphyrin-nanotube composites are, by and large, mainly in the photovoltaic [154-156] and optoelectronic [157,158] fields, that are out of the scope of the present chapter. Nevertheless, a number of interesting reactions have been investigated with porphyrin-CNT systems that can be regarded as nanoreactors. Moreover, being monodimensional conducting polymers, they are expected to play a role in different nanotechnology fields [159,160]. 

Franco R, Jacobsen JL, Wang H, Wang Z, Istvan K, Schore NE, Song Y, Medfoith CJ, Shelnutt JA (2010) Molecular organization in self-assembled binary porphyrin nanotubes revealed by resonance Raman spectroscopy. Phys Chem Chem Phys 12 4072-4077... 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

Esterification constitutes a valuable alternative to the amidation strategy. As with amidation, the formation of the ester bond is performed following a first reaction step with acyl chloride. The ester bond has been extensively utilized to attach many organic and inorganic moieties. Porphyrins are a classic example of substrates covalently bound via esterification strategies their photoinduced electron transfer to the nanotube has been studied for applications in molecular electronics and photovoltaic devices (Fig. 3.6) [21]. 

Fig. 3.6 Photoinduced electron transfer from porphyrins linked through ester bond to the carbon nanotube sidewalls. Adapted with permission from [21], 2005, American Chemical Society.

Porphyrins are also able to directly interact with the nanotube sidewalls. For example, tetraphenyl porphyrin (H2-TPP) has been reported to interact with nanotubes to form TPPs/CNTs compounds that are stable for days. Stability has been enhanced by using a micelle-assisted approach, leading to stable structures with potential applications in light harvesting devices [76]. 

Metal coordination to the porphyrin negatively affects the interaction with the nanotubes, with adsorption depleting according to the metal used [77]. 

Palacin, T., et al., Efficient Functionalization of Carbon Nanotubes with Porphyrin Dendrons via Click Chemistry. Journal of the American Chemical Society, 2009.131(42) p. 15394-15402. 

Zhao, H., et al., Synthesis, characterization, and photophysical properties of covalent-linked ferrocene-porphyrin-single-walled carbon nanotube triad hybrid. Carbon, 2012. 50(13) ... 

D Souza, F., et al., Self-assembled single-walled carbon nanotube-.Zinc-porphyrin hybrids through ammonium ion-crown ether interaction Construction and electron transfer. Chemistry - A European Journal, 2007.13(29) p. 8277-8284. 

Hijazi, I., et al., Formation of Linear and Hyperbranched Porphyrin Polymers onto Carbon Nanotubes via CuAAC Grafting from" Approach. Journal of Materials Chemistry, 2012. 22(39) p. 20936. 

Photochromism has also been observed when two porphyrinic groups are linked to a dithienylethene scaffold. The closed form showed an absorption band at 560 nm (01JA1784). The same behavior was observed in the system 318-319 (02AM918). Dithienylethene photochromic systems have also been described to be linked to single-walled nanotubes (07JA12590). 

Construction of organic nanotubes starting from porphyrin dendrimers with core/shell architecture is also feasible. Figure 8.29 also shows how covalent nanotubes can be produced by removal of the dendritic component of the molecule. A coordination polymer is first synthesised from a dendritic metallopor-phyrin with alkene end groups. This is subjected to intramolecular and intermo-lecular crosslinking by ring-closing metathesis at the periphery. 

Li s porphyrin rosettes (18) [22], Yagai s photoswitchable rosettes (19) [23], and Fenniri s nanotubes (20) [24] nicely illustrate the former approach. Thus, CA3M3 rosettes (Figure 3.7) endowed with a pyridine moiety at the melamine component and a strapped Zn-porphyrin (to enhance coordination from only one side of the ring) at the cyanuric acid component are more stable than the CA3 M3 model rosette initially reported by Whitesides. Even more complex versions of the same concept, involving one all-pyridine rosette and one all-porphyrin rosette to self-assemble into double rosettes were studied, although only NMR evidence was presented [22],... 

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. 

Takagi S, Eguchi M, Tryk DA, Inoue H. Porphyrin photochemistry in inorganic/organic hybrid materials clays, layered semiconductors, nanotubes and mesoporous materials. J Photochem Photobiol C Photochem Rev 2006 7 102-26. 

FIGURE 2.2 Supramolecular nanostructures for light driven energy and electron transfer. This research is focused on rational design and study of self-assembled porphyrin, fullerene, and carbon nanotube bearing supramolecular complexes and nanostructures. 

Tu WW, Lei IP, Ju HX (2009) Functionalization of carbon nanotubes with water-insoluble porphyrin in ionic liquid direct electrochemistry and highly sensitive amperometric biosensing for trichloroacetic add. Chem Eur J 15 779-784... 

Figure 5.14 Schematic diagram for the self-assembly of tin(IV) porphyrin-containing dendrimer into nanotubes. (From Kim et al.73)...

Figure 3.84 (a) Example of a porphyrin employed for the noncovalent functionalization of nanotubes, (b) HRTEM image of a carbon nanotube surrounded by hollow spheres of MgO ( RSC 2004). 

Another important discovery has been reported in 2004. A typical mixture of metallic and semiconducting SWNT was treated with a derivative of porphyrine (Figure 3.84a). Actually one succeeded in selectively functionalizing the semiconducting species and consequently transferring them into solution, while the metallic tubes did not react and thus remained in the sediment. This procedure might once enable the separation of both types of nanotubes on a larger scale. This would be of eminent importance for the construction of electronic devices from nanotubes. 

Besides the substances mentioned so far, functionalized fuUerenes like the simple Bingel adduct can be intercalated into nanotubes as well (Section 2.5.5.2). The formation of peapods has further been described for metallocenes (e.g., ferrocene), porphyrines (e.g., erbium phthalocyanine complex) and small fragments of nanotubes. The most important prerequisite for the feasibility of inclusion is always a suitable proportion of sizes of both the tube and the structure to be embedded. For example, this effect can be observed for the intercalation of different cobaltocene derivatives into SWNT. The endohedral functionalization only takes place at an internal diameter of 0.92nm or above (Figure 3.100). But there is also an upper limit to successful incorporation. When the diameter of the nanotube is too large, the embedded species can easily diffuse away again from the host. Only few molecules are consequently found inside such a wide tube. 

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