Porphyrins self-complementary coordination

Kind R (2007) Evidence for Ferroelectric Nudeation Centres in the Pseudo-spin Glass System Rbi x(ND4)xD2P04 A 87Rb NMR Study. 124 119-147 Klapotke TM (2007) New Nitrogen-Rich High Explosives. 125 85-121 Kobuke Y (2006) Porphyrin Supramolecules by Self-Complementary Coordination 121 ... 

Kobuke Y (2006) Porphyrin Supramolecules by Self-Complementary Coordination 121 49-104... 

This chapter focuses on supramolecular porphyrin systems that are stable enough to be characterized in solution. Assemblies coordinated only in solids (e.g., crystals) will not be included. In order to maintain these supramolecular structures in solution, strong complementarity and multitopic coordinations are required, rather than a simple monotopic axial coordination. Of these conditions, this discussion will be concerned only with those necessary for the complementary coordinations, and with the presentation of various examples of these coordinations. The issue of multitopic coordination will be dealt with in another forum. Self-complementary coordination can be used to obtain dimers, rings, and one- and two-dimensional arrays. These supramolecular systems should not only influence structure formation, however, but also be closely related to their functions. It is therefore natural to discuss the... 

Pyridyl ligands are certainly candidates for forming stable self-complementary coordination assemblies and are conventionally employed for supramolecular structure formation. Zn and Mg complexes of meso- and b-pyr-role-substituted 2-pyridylporphyrins (4a-c) were therefore prepared [37,38]. Crystallographic analysis was used to verify that the required slipped cofacial arrangement had been generated, and demonstrated the overlapping of one of the pyrrolic rings in each porphyrin. This confirmed the structural similarity between the sample and the special pair. The stability constant was reported to be 5 x 10 for the Mg dimer of the meso-pyridyl case 4b. 

As described in Sect. 2, imidazolyl zinc porphyrin is an excellent candidate for self-complementary coordination due to its extremely large stability constant. In order to arrange these complementary coordination units into a hexam-eric macrocycle, two imidazolyl zinc porphyrins were connected through an m-phenylene group to fix the angle at 120 , offering a gable porphyrin... 

Self-complementary dimer formation of imidazolyl zinc porphyrin allowed two such units to be connected directly at their meso positions to give 51. Since the two coordination assembhes grow in opposite directions in this case, successive self-complementary coordination leads to a Unear multi-... 

In this way, self-complementary coordination developed in the field of porphyrin chemistry was successfully transferred to a related field, and has been shown to be a successful first step toward similar advances in phthalocyanine chemistry. Since phthalocyanine has several advantages over other materials in a range of important applications, this development should open up the field of supramolecular chemistry in phthalocyanines as an area of much more active research. 

A linear assembly formed through successive self-complementary coordination of meso-meso-coupled bis(imidazolyl zinc porphyrin) units can also transfer excitation energy along the one-dimensional array. In order to estimate the efficiency of this energy transfer, imidazolyl Mn porphyrin was added to the linear array of imidazolyl zinc porphyrins 52. The terminals of the array can accept complementary coordination with imidazolyl Mn porphyrin [114], As a result, the fluorescence of Zn porphyrin (0 = 0.053) in the one-dimensional array is quenched. This quenching never happens... 

Fig. 37 Scheme of photocurrent generation. A porphyrin antenna was grown from a SAM on a gold surface by self-complementary coordination followed by covalent immobilization by a ring-closing metathesis reaction... 

A particularly intriguing kind of supramolecular self-assembly by axial coordination to metaUoporphyrins, namely self-complementary coordination, is reviewed in the second chapter by Yoshiaki Kobuke. Self-complementarity affords large stability constants. The fascinating systems described in Kobuke s contribution were prepared and investigated as models for components of photosynthetic natural systems self-complementary dimers of porphyrins mimic the special pair of the photosynthetic reaction centers, while macrocychc and three-dimensional porphyrin supramolecules were prepared as photosynthetic antenna models. 

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