1,4-phenylene bridges

Of special significance in the development of PMO materials was the synthesis of porous materials with crystalline order of the bridged silsesquioxane inside the framework walls, initially achieved through the use of tt-tt interactions between 1,4-phenylene-bridged silsesquioxane precursors.33 Molecular scale periodicity in... 

Oakley and co-workers have synthesized the related 1,4-phenylene-bridged bis-lA ,2,4,6,3 i -thia(selena)triazaphosphinines and studied the spin distribution in the diradicals (262) <92IC442>. The closed shell quinoidal ground state (263) evidently does not prevail. 

The synthesis was recently extended from grid porphyrin arrays to soluble windmill arrays [109]. Flanking with a peripheral Ni p-octaalkylporphyrin was achieved by Ag(I)-promoted coupling reactions of 1,4-phenylene-bridged linear porphyrin arrays, which are composed of a central Zn P-free porphyrin. Up to 48 porphyrin rings were connected. Efficient singlet energy transfer from the peripheral porphyrins to the central Zn-porphyrins was found. 

An extension of this work was reported for orthogonally arranged, windmill-like porphyrin arrays, involving a 5,10,15,20-linked porphyrin dimer urnt. The synthesis involved the preparation of a symmetric, linear 1,4-phenylene-bridged porphyrin trimer. The reaction of the trimer with two equivalents of AgPFe produced windmilllike porphyrin hexamer and nonamer systems (Figure 52). 

Synthesis of 1,4-phenylene bridged bis-heterocyclic compounds 12ARK(1) 1. Synthesis of small and medium size monocycHc hydroxamic acids 12KGS699. 

Si), 1 1,4-phenylene-bridged liquid crystalline polysiloxane containing ester-based mesogenic side groups, copoly(arylene-l,2-dioxy/oligo-diem-... 

Dembek and coworkers have reported that high MW polyamides coordinated to Cr(CO)3, such as 16 (shown in Scheme 3) display nematic Uquid crystalline texture. This indicated that the rigid-rod nature of the 1,4-phenylene bridged polymer was retained on metal coordination even though its solubUity was enhanced significanfly. The intrinsic... 

Park GJ, Nakajima S, Osuka A, Kim K. 1995. Electrocatalytic four-electron reduction of dioxygen by 1,2-phenylene-bridged dicobalt diporphyrins. Chem Lett 255. 

I2 as a probe for aromatic rings in phenylene-bridged periodic mesoporous organosilica... 

Keywords PMO, BTEB, Phenylene-Bridged, Iodine, UV-Visible. 

Phenylene-bridged periodic mesoporous organosilicas, with both amorphous and crystal-like walls, (referred to in the following as AW-Ph-HMM and CW-Ph-HMM, respectively) were synthesized and characterized as previously reported [6,7]. BTEB was used as a precursor for both solids the surfactant was Brij-76 (Ci8H37(OCH2CH2)nOH) in acidic media for AW-Ph-HMM and octadecyl-trimethylammonium bromide(ODTMA) in basic media for CW-Ph-HMM. A purely siliceous MCM-41 sample was also synthesised, the first step being the solution of octadecyltrimethylammonium bromide in a basic aqueous solution (NH3), kept a 333 K. Tetraethyl orthosilicate (TEOS) was then added in all cases dropwise, and the mixture stirred for 24h at room temperature (H20 34.2 g/ NH3 (15%) 8.52 g/ ODTMA 0.73 g TEOS 3.24 g). After further 24 hours in hydrothermal conditions at 368 K, the sample... 

Figure lb reports the UV-Visible spectrum of the liquid 1,4-bis(triethoxysilyl)benzene, the precursor of the phenylene-bridged PMO, into which traces of iodine have been dissolved. Only one band due to iodine is visible at 362 nm. We suggest this band to be due to I3" ion, which in aqueous solution absorbs at 355 nm [8], The presence of a band at the same wavelength in the case of I2 adsorbed onto AW-Ph-HMM reveals, also in... 

Iodine molecules adsorbed onto the structural aromatic rings provide information on the electron-donor strength, which appears to be higher in phenylene-bridged PMO than that reported for benzene and comparable with that reported for p-xilene. Traces of I3" species were also detected. From a comparison between two phenylene-bridged PMOs with different degree of order in the walls, aromatic rings in the material with amorphous walls appear more available for interaction with iodine. 

With the alkynyl functionality greater than two, starbust type complexes are obtained, as derived, for example, from 1,3,5-trialkynylbenzenes 85 or -triazines,86 1,1,2,2-tetraalkynylethenes,85 or bis(l,2-dialkynyl)phenylene-bridged crown ethers or calixarenes. ... 

Aromatic spacers have also been used thus it could be shown for a phenylene-bridged diporphyrinyl system that electron hopping between both subunits can occur (Huber et al, 1990). Here the phenylene bridge is twisted out of conjugation with the two porphyrin rings, and the effect is observed for 1,4-(para) [45a] and the 1,3-(meta) [45b] substitution. 

Q. Chu, Y. Pang, L. Ding, and F.E. Karasz, Green-emitting PPE-PPV hybrid polymers efficient energy transfer across the m-phenylene bridge, Macromolecules, 36 3848-3853, 2003. 

Et2C2B3H2Cl)Co(Et2C2B3H2Cl)Co(C5Me4)]3(C6H4)4 phenylene-bridged ... 

The electronic and magnetic properties of bridged dimetallic complexes such as 104 and 105 have been explored. Oxidation of the CoII-Co11 phenylene-bridged species 104 affords the mixed valence Con-Com complex and the diamagnetic CoIII-Co111 dication.128 Magnetic, IR, and electrochemical evidence on neutral 104 indicates weak Co-Co interaction. 

Dentritic phenylene-bridged Bi bismuthanes were obtained from Ph2BiCl and />-Li2C6H4 and related reagents.144... 

Fiereby, Vq refers to the maximal electronic coupling element and p is the decay coefficient factor (damping factor), which depends primarily on the nature of the bridging molecule. From the linear plot of In ETmax versus R the p value is obtained as 0.60 A [47]. This p value is located within the boundaries of nonadiabatic ET reactions for saturated hydrocarbon bridges (0.8-1.0 A ) and unsaturated phenylene bridges (0.4 A ) [1-4,54,55]. 

If the properties of the various dinuclear complexes investigated appear to be very sensitive to both factors, we can nevertheless discriminate them roughly (and in a somewhat artificial way) by discussing the data obtained for the family of methylene-bridged knots and related unknotted complexes and, separately, those obtained for the phenylene-bridged knots. 

Table 2. Electrochemical and photophysical properties of dicopper(I) and heterodinuclear knots containing the m-phenylene bridge.

Special features strongly related to the compactness of the phenylene-bridged knots were also observed during the photophysical studies. All die compounds, as usual for copper complexes with phenanthroline-type ligands [116, 117], exhibit MLCT luminescence in CH2C12 at room temperature. Only one emission band, assigned to the lowest MLCT excited state, is observed even for the complexes con-... 

The most easily identifiable characteristics are those related to the shape of the complexes, with their double-stranded helical cores. In this respect, the electrochemical and photochemical properties of Cu2(K-84)2+ are not much different from those of the open-chain helical precursor or its O-methylated version. The strong electronic coupling between the two copper centers is clearly a consequence of the 1,3-phenylene bridges between the two complex subunits and the topological properties of the ligand have virtually no influence. 

The complexes in which the ethylene bridge has been replaced by a phenylene bridge are considerably more stable to oxidation, and a... 

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