Nanoscopic Photoluminescence Memory as a Fingerprint of Complexity in Self‐Assembled Alkyl/Siloxane Hybrids

Abstract

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...

Lanthanide‐Containing Light‐Emitting Organic–Inorganic Hybrids: A Bet on the Future

“…[136] The lamellar monoamidosil host framework, which exhibits a reversible order-disorder phase transition with onset at about 96 8C, was obtained by means of sol-gel reactions and a self-assembly process involving intermolecular hydrogen bonding between the amide groups, partially interdigitated van der Waals packing, and an entropic term related to the phase separation. [137] The incorporation of the lanthanide ions (introduced as a trifluoromethanesulphonate -or simply triflate-salt) into the monoamidosil network induced the growth of a new lamellar phase that coexists with the original phase of the pristine material.…”

“…[135,136] The design and structuring of these hierarchically-structured Ln 3þ -containing hybrids result from an extension of the method employed previously to produce highly organized lamellar monoamide [137] and diurea cross-linked alkyl/siloxanes, [138] and highlights the importance of combining sol-gel methods and self-assembly processes.…”

Self‐Assembly of Alkyl‐Substituted Cubic Siloxane Cages into Ordered Hybrid Materials

“…The 29 Si MAS NMR spectrum of 1 H after calcination (Figure 7c) shows broad signals corresponding to the Q 3 and Q 4 units, suggesting that the CSiO 3 (T) unit was converted to SiO 4 (Q) unit by thermal cleavage of Si À C bonds. The relative intensity ratio of the…”

Nanostructuring of Ionic Bridged Silsesquioxanes

“…[7] The presence of self-assembling groups, such as long alkylene chains, [7b, d, 8] aromatic fragments, [9] or urea, [7a, b, 8d] amide, [10] or carbamate [11] functions, in the organic moiety of the starting organosilane allows the formation of regular structures with well-defined morphologies.…”