Complex structures, such as living organisms or highly structured materials, have in common the fact that their inherent complexity may be accounted for by the tangled organization of a vast number of simple units. The complex behavior arises not necessarily from the atomic structure of the system, but from the orderly assembly of all, or part, of its constituents.[1,2] Self-assembly of synthetic soft-matter componentssuch as polymers, liquid crystals, surfactants, colloids, and organic/inorganic hybrids-results in regular hierarchically organized structures. [3][4][5] The importance of combining sol-gel methods and self-assembly routes to synthesize hierarchically structured organic/inorganic materials, with potential applications in the design of ion-transport microdevices, has been highlighted recently.[5]Silsesquioxanes ((RO) 3 -Si-R′-Si-(OR) 3 , where R and R′ are organic groups) and organosilanes (R′-Si-X 3 , where X = OR or Cl) are examples in which hierarchically ordered self-assembled architectures with well-defined morphologies at the macroscopic scale-such as ribbons stacked into lamellae, [6][7][8][9] 2D hexagonal structures, [9] twisted helical fibers with controlled handedness, [10] hollow tubes and spheres, [11] ladderlike superstructures, [12] and bilayered lamellar packing [13][14][15] are induced by weak interactions between the R′ organic spacers (hydrogen bonding, hydrophobic interactions, and p-p interactions).Despite the fact that work on silsesquioxanes has produced hierarchically ordered architectures, [6][7][8][9][10][11][12] so far the self-assembly of the simpler trifunctional alkylsilanes has been reported only sporadically. [13][14][15] In these examples, the design strategy relies on the self-organization of organophilic precursor molecules that become amphiphilic as hydrolysis proceeds to form hydrophilic silanol groups. As the hydrophilic parts (head groups) of alkylsilanetriols occupy less space than the hydrophobic ones, lamellar packing is favored. This anisotropic aggregation mechanism of alkyltrihydroxysilane species resembles that of amphiphilic surfactants and phospholipid molecules. Like the L-phase (lamellar phase) of phospholipids, alkylsilanes are characterized by a bimolecular layered pattern of stacks of alkyl chains perpendicular to the layers. The only known examples of bilayered lamellar packing in alkylsilanes are the microcrystalline poly(octadecylsiloxane)s prepared from n-alkyltrichlorosilanes, [13] and the hybrids synthesized from triethoxy- [14] and trimethoxy-based [15] alkylsilanes. Hydrophobic interactions between the organic chains are the main force driving the formation of these highly ordered packing structures. Although the relationship between structural complexity and self-assembly mechanisms has been given much consideration, the essential role played by higher organizing principles in determining emergent physical phenomena in soft-matter complex structures, although recognized (e.g., for the unpredictable electronic features of cholesterol-stilben...

Single crystals of the {Fe (II)(pyrazine)[Pt(CN) 4]} spin crossover complex were synthesized by a slow diffusion method. The crystals exhibit a thermal spin transition around room temperature (298 K), which is accompanied by a 14 K wide hysteresis loop. X-ray single-crystal analysis confirms that this compound crystallizes in the tetragonal P4/ mmm space group in both spin states. Within the thermal hysteresis region a complete bidirectional photoconversion was induced between the two phases (high spin right arrow over left arrow low spin) when a short single laser pulse (4 ns, 532 nm) was shined on the sample.

Sol-gel derived poly(oxyethylene)/siloxane hybrids (di-urethanesils) doped with europium triflate, Eu(CF 3 SO 3 ) 3 , were examined by XRD, 13 C and 29 Si MAS NMR and FT-IR, FT-Raman, and photoluminescence spectroscopies. The host framework of these materials consists of a siliceous network grafted through urethane linkages to both ends of polymer chains with 6 oxyethylene repeat units. Xerogels with ∞ g n g 1 (where n is the molar ratio (OCH 2 CH 2 )/ Eu 3+ ) were analyzed. The compounds with n g 10 are amorphous. In samples with n e 5 crystalline Eu(CF 3 SO 3 ) 3 was detected. In the di-urethanesils with n g 10 the cations interact with the urethane carbonyl oxygen atoms. The complexation of the polyether chains to the cations is initiated at approximately n ) 10. At n e 10 both types of cation bonding situations occur. "Free" and weakly coordinated CF 3 SO 3ions exist in the whole range of salt concentrations analyzed. Ionic aggregates are formed in samples with n ) 5 and 1. For 200 g n g 20 the emission quantum yields range from 0.7 to 8.1%. The decrease in the quantum yield with the increase of the Eu 3+ concentration markedly depends on the activation of the energy transfer between the hybrid host's emitting centers and the cations, permitting, therefore, a fine-tuning of the emission chromaticity across the CIE (Commission Internationale d'E Ä clairage) diagram (e.g., (x, y) color coordinates from (0.19, 0.18) to (0.50, 0.49), for n ) 200 and 5, respectively).

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Novel amide cross-linked alkylene/siloxane hybrid materials (di-amidosils) synthesized by the sol-gel process have been investigated. Two samples identified by the notation d-A(x) with x = 4 and 8 (where x is the number of methylene groups of the alkylene chain) have been produced as transparent, amorphous, rigid monoliths, thermally stable up to about 381 and 400 ºC, respectively. In the d-A(8) hybrid the siliceous framework is composed of [(SiO) 3 Si(CH 2)-] and [(SiO) 2 (HO)Si(CH 2)-] substructures. Structural unit distances of 4.1 and 4.2 Å and average interparticle distances of 12 and 17 Å have been determined for d-A(4) and d-A(8), respectively. In these compounds the alkyl chains are disordered and adopt gauche conformations. While a negligible proportion of the amide linkages remain non-bonded, the great majority of these groups belong to highly disordered strong hydrogen-bonded amide-amide associations. The hybrids introduced are room temperature white light emitters, presenting an emission large, broad band in the blue/purplishblue spectral region. The origin of such band have been ascribed to the convolution of donoracceptor pair (D-A) recombinations that occur in the NH groups of the urea linkages and in the siliceous nanodomains. The maximum quantum yield value of the d-A(8) di-amidosil is 5.4 %.

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Nd(3+)-based organic/inorganic hybrids have potential application in the field of integrated optics. Attractive sol-gel derived di-urea and di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils and di-urethanesils, respectively) doped with neodymium triflate (Nd(CF(3)SO(3))(3)) were examined by Fourier transform mid-infrared (FT-IR), Raman (FT-Raman), (29)Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and photoluminescence spectroscopies, and small-angle X-ray scattering (SAXS). The goals of this work were to determine which cation coordinating site of the host matrix (ether oxygen atoms or carbonyl oxygen atoms) is active in each of the materials analyzed, its influence on the nanostructure of the samples and its relation with the photoluminescence properties. The main conclusion derived from this study is that the hydrogen-bonded associations formed throughout the materials play a major role in the hybrids nanostructure and photoluminescence properties.