Porphyrins covalently linked assemblies

A suspension obtained from the water-solnble anionic mew-tetrakis(4-carboxyphenyl)porphyrin and MWCNTs was nsed as an optical probe for DNA detection [242]. The same target was achieved very recently, constructing a supramolecular assembly with the water-soluble anionic 5-(4-aminophenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin, covalently linked to MWCNTs and complexed with cyclodextrins (CD, either a-CD or P-CD) [243]. 

Molecular assembly 2, composed of a porphyrin chromophore covalently linked to a benzoquinone electron acceptor and a carotenoid polyene as electron donor provides an electron donor/photosensitizer/electron acceptor (D-S-A) configuration [34]. The sequential ET reactions occurring in the triad upon photoexcitation of the porphyrin center are outlined as follows (where C, P, and Q stand for the carotenoid polyene, porphyrin, and quinone components, respectively) ... 

Two of the classical bis-nitrogen ligands to assemble porphyrins (predominantly zinc metallated) are the bidentate l,4-diazabicyclo[2.2.2]octane (DABCO) and 4,4 -bipyridine (bipy). Other di-topic nitrogen-ligands studied include hydrazine, 4,4 -bipyrimidine, diaza-pyrene, 5,5 -dicyano-2,2 -bipyri-dine, perylene-bisimide, extended bipyridine units and non-covalently linked di-pyridyl ligands via bipy-metal interactions. The formation of various bis-porphyrin and multiporphyrin assemblies using these versatile ligands were studied in detail by Sanders, Anderson, Hunter, Branda and many others. The structures of the supramolecular multi-porphyrin architectures are schematically represented in Fig. 9. 

The covalently linked or self-assembled systems constructed from free-base porphyrins or metalloposphyrins and various quenchers and related studies of excited-state energy-transfer and electron-transfer processes in such systems are a widely studied topic of contemporary supramolecular chemistry. There are two major reasons for the exceptional interest in the topic a challenge to synthesize artificial systems for harvesting solar energy of... 

The covalently linked bis-Zn(II) bis-porphyrins used by Rempel and coworkers - as platforms for two-point attachment of 5,15-bis(3-pyridyl)porphyrin 64, leading to parallel arrangements of porphyrins, were also used for two-point coordination of 5,10-bis(4-pyridyl)porphyrin 58 or 5,10-bis(3-pyridyl)porphyrin 63, that is, porphyrins in which the pyridyl arms are in cw-relative orientations (Figure 41). In the case of 58, a binding constant of 2.4 X lO mol" L was observed for the assembly 80,... 

D Souza, F., G.R. Deviprasad, M.E. Zandler, M.E. El-Khouly, M. Fujitsuka, and O. Ito (2002). Electronic interactions and photoinduced electron transfer in covalently linked porphyrin-C6o(pyridine) diads and supramolecular triads formed by self-assembling the diads and zinc porphyrin. J. Phys. Chem. B 106(19), 4952-4962. 

Since functionalization of the graphene with a porphyrin was reported for the first time [166], photovoltaic properties of this type constructs have intensively been studied. Photovoltaic properties of an assembly of the covalently linked free-base me o-tetraphenyl porphyrin with graphene oxide were evaluated [167]. The IPCE spectrum of this conjugate resembled the UV-vis absorbance spectrum of the porphyrin used reaching merely 1.5 % at the Soret band wavelength. 

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