Periodic mesoporous organosilicas (PMOs) represent an exciting new class of organic-inorganic nanocomposites targeted for a broad range of applications such as catalysis and sensing, separations, and microelectronics. Their hallmark is the presence of organic bridging groups incorporated into the channel walls of an ordered nanoporous structure, which represents a useful tool to finely tune the chemical and physical properties of the materials. We discuss the history of the discovery and development of the PMOs emphasizing the most important recent advancements regarding compositions and structures, morphologies, and properties. Furthermore, we present an outlook about the promising future perspectives of PMOs that result from the latest developments in this field.

Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C2H5O)3Si–R–Si(OC2H5)3 or R′–[Si(OC2H5)3]3 with R = methene (–CH2–), ethylene (–C2H2–), ethene (–C2H4–), 1,4‐phenylene (C6H4), and R′ = 1,3,5‐phenylene (C6H3). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and 29Si and 13C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH2 and C2H4 compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.

In this study we report the synthesis of a new class of materials called hybrid periodic mesoporous organosilicas (HPMOs). By coupling a silsesquioxane precursor through at least two chemical linkages to the mesopore walls of a pre‐existing periodic mesoporous silica (PMS) or periodic mesoporous organosilica (PMO). Many of the problems of a conventional PMO material can be avoided while ensuring efficient use of the bridging organic functional groups of the silsesquioxane. We demonstrate this concept for PMS by anchoring various silsesquioxanes, such as ethene and ethane silsesquioxanes, to the mesopore walls of the PMS. The addition of anchored silsesquioxane monolayers and multilayers to the mesopore walls also allows for the strict control of the diameter of the mesopore as well as the mesopore wall thickness in the final HPMO material. Additionally it is shown that having the silsesquioxane located solely on the surface of the mesopores in HPMOs gives increased chemical accessibility of the organic bridge‐bonded moiety when compared with their PMO counterparts containing the bridge‐bonded organic both on the surface and within the pore walls.

Here we report the first documented synthesis of a periodic mesoporous organosilica (PMO), that contains a multiply bonded C60 moiety integrated into the silica channel walls of the material, dubbed C60-PMO. This is accomplished through the acid-catalyzed co-assembly, of C60(NHCH2CH2CH2Si(OEt)3)x and tetraethylorthosilicate (TEOS) with a polyethyleneoxide-polylpropyleneoxide-polyethyleneoxide triblock copolymer template. The percentage of C60 in the final material was estimated to be a minimum of 63 vol %, but potentially as high as 91 vol %. The effects of the synthesis conditions on the mesostructure of the resulting materials are examined. In particular, we demonstrate that the C60 is uniformly distributed throughout the entire sample by the use of energy dispersive X-ray fluorescence (EDX) analysis and an OsO4 label bonded to the C60.

Organic chemistry Z 0200 Past, Present, and Future of Periodic Mesoporous Organosilicas -The PMOs -[44 refs.]. -(HATTON, B.; LANDSKRON, K.; WHITNALL, W.; PEROVIC, D.; OZIN*, G. A.; Acc. Chem. Res. 38 (2005) 4, 305-312; Dep. Chem., Univ. Toronto, Toronto, Ont. M5S 3H6, Can.; Eng.) -Lindner 34-319