Self assembly dimers

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

The indium complexes In(Se2PPh2)3 L (where L = THF, MePh) are self-assembled dimers in solid state through Se- Se secondary interactions.450... 

Figure 11, View of the self-assembled dimer formed from sapphyrin 5 in the presence of trifluoroacetic acid. This X-ray structural figure was generated information downloaded from the Cambridge Crystallographic Data Centre and corresponds to a structure originally reported in ref. 21. Atom labeling scheme carbon C nitrogen oxygen fluorine phosphorous hydrogen o. Selected hydrogen atoms...

Acceleration of a Diels-AIder reaction by a self-assembled dimeric capsule... 

Figure 8.2.3. Schematic view of self-assembled dimer composed of two catenane.

Figure 5.8 Self-assembled dimer of 5.25 with Na+ binding by a guanosine tetramer motif (G-quartet) and Cl- binding by amide functionalities. Remaining space if filled by water molecules. (Reproduced with permission from [22] 2003 American Chemical Society).

Fig. 14.9 Anthracene-9- and -1-carboxylic acids (12 and 13), showing the square self-assembled dimer of 12 leading to columnar...

The principal idea of this present essay was to show how the unique preorganization of functional groups in self-assembled dimers of tetra-urea calix[4]arenes can be used to prepare novel multi-rotaxanes and -catenanes or topologically even more complex molecules and supramolecular structures. We will conclude by summarizing some related studies in which calixarenes were used in a different way as building blocks for the construction of such structures or assemblies. 

Similarly, the analog 54 also forms a self-assembled dimer [54]2 in non-polar solvents. In the presence of pyridine, the dimer dissociates into the monomeric species 54 Py [53,54], Further addition of AgPF6 leads to the formation of a novel Ag-linked phthalocyanine dimer [54]2Ag PF6 (Scheme 5) [55]. On the basis of its electronic absorption and magnetic circular dichroism properties, it has been suggested that this dimer adopts a planar and nms-con formation. Addition of NH4C1, which can remove the silver ions as AgCl, regenerates the monomeric 54 Py. 

The photophysical properties of the self-assembled dimer [54]2 have been studied in detail with various spectroscopic and computational methods [53,54], In the lowest excited singlet (Si) state, the excitation delocalizes over the two macrocycles, and the non-radiative decay is enhanced by dimerization. By contrast, the exciton interaction is very weak in the lowest excited triplet (Ti) state. In the excited-state absorption spectrum recorded in 1-decane, two sharp bands at 658 and 694 nm are observed, which can be attributed to the Q bands of the Tx self-assembled phthalocyanine dimer. 

They also form self-assembled /-dimers in non-coordinating solvents probably through coordination of one of the diethylamino nitrogen atoms with the central metal of adjacent molecule. Upon addition of pyridine, they are converted back to the monomeric species. The fluorescence is significantly quenched and the efficiency of singlet oxygen formation is also reduced as a result of intramolecular photoinduced electron transfer, which is inhibited in the dimers. 

Haino and co-workers have reported the synthesis of a self-assembling dimeric capsule via metal-coordination utilizing two octadentate resorcin[4]arene cavitands possessing four bipyridyl groups (13) which complex four silver cations (Ag+) in a tetrahedral fashion (Fig. 4) [46, 47]. A detailed computational study of the dimeric metallo-capsule 14 revealed a large and elaborate three-dimensional inner capsular... 

Vlckova et al. demonstrated single-molecule SERS in self-assembled dimers of silver nanoparticles [161]. The self-assembly process was driven by nanoparticle functionalization with a bifunctional molecular linker (4,4 -diaminoazobenzene) which forms a molecular bridge between the particles. Molecules forming the molecular bridge are then precisely positioned within the hot spot with the molecular population being controlled by careful optimization of the linker to... 

Figure 10.5.17 View of the Self-assembled Dimer Formed from Sapphyrin 10.30 in the Presence of Trifluoroacetic Acid.

Control of self-assembly and reversible encapsulation of xenon in a self-assembling dimer by acid-base chemistry, N. Branda, R. M. Grotzfeld, C. Valdes and J. Rebek, Jr, J. Am. Chem. Soc., 1995, 117, 85. 

The strongest complex was that of difluorobenzene. Stability favors the best fit that leaves no empty space in the cavity. The self-assembled dimer of the urea in (7.9) (where R = ethoxycarbonyl) encapsulated methane but not ethane Hydrogen bonding is also important in the sheet-like... 

Figure 13. X-ray crystal structure of (12-H )z self-assembled dimer. The calixpyrrole macrocycles both adopt the cone conformation as is observed in other calixpyrrole anion complexes. Crystal structure originally published in Sessler, J. L. Andrievsky, A. Gale, P. A. Lynch, V. Angew. Chem. Int. Ed. Engl. 1996, 35, 2782-Diagram produced using data from the Cambridge Crystallographic Database.

Boijesson K, WoUer JG, Parsa E, Martensson J, Albinsson B. A bioinspired self assembled dimeric porphyrin pocket that binds electron accepting ligands. Chem Comm. 2012 48 1793-1795. 

Distinction should be made between the self-assembled dimeric or trimeric species dted above and authentic heterocycles in which the metal(III) is three-coordinate, e.g. the four-membered ring derivatives R2M2E2R 2, 20, and the six-membered ring derivatives R3M3E3R 3, 21. 

Extensive studies have been performed on self-assembled dimeric and trimeric or-ganogallium phosphides, 86 and 87, and arsenides, 88 and 89, in relation to their use as precursors for gallium phosphide and gallium arsenide semiconductors [237-240]. Their association in solution was observed some time ago as a result of molecular weight determinations in solution [158, 160] and many of the compounds have been structurally characterized. As already shown, the degree of association depends upon the steric bulkiness of the organic groups. 

In the solid state, the dinuclear anions [Me2As2Cl5] are self-assembled dimeric supermolecules, 150, with As- -Cl secondary bonds (3.126 and 3.365 A) [380]. 

Ala Kleme T, Latva M, Haapakka K (2000) Radiative D4- F dynamics of terbium in self-assembled dimeric chelates. Anal Chim Acta 403 161-171... 

Another p-modified derivative, p-benzo-fused 17b, which possesses an extended TT-structure, provided a mesophase with TATA Cl as a tetragonal columnar (Coltet) phase with a = 4.21 nm and c = 0.73 nm based on a tetrameric assembly (Z = 4.02 forp = 1) (Fig. 4.12a). The mesophase range of 17bCl -(TATA ) was 24-102 °C. On the other hand, anion-free 17b formed a mesophase (33-166 °C) based on a Coin phase (a = 4.15 nm and c = 0.42 nm) consisting of a self-assembled dimer unit. In contrast to the assembled mode of the Colh structure of 14c C1 -(TATA - ), the receptor unit in 17b Cl -(TATA )+ faces the center of the circular unit with anions arranged on the inside, presumably because of the positions of the alkyl chains at the fused-benzo units at the p-positions of the pyrrole [31e]. 

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