Periodic mesoporous organosilicas (PMOs) prepared by surfactant-directed polycondensation of bridged organosilane precursors are promising for a variety of next-generation functional materials, because their large surface areas, well-defined nanoporous structures and the structural diversity of organosilica frameworks are advantageous for functionalization. This critical review highlights the unique structural features of PMOs and their expanding potential applications. Since the early reports of PMOs in 1999, various synthetic approaches, including the selection of hydrolytic reaction conditions, development of new precursor compounds, design of templates and the use of co-condensation or grafting techniques, have enabled the hierarchical structural control of PMOs from molecular- and meso-scale structures to macroscopic morphology. The introduction of functional organic units, such as highly fluorescent π-conjugates and electroactive species, into the PMO framework has opened a new path for the development of fluorescent systems, sensors, charge-transporting materials and solid-state catalysts. Moreover, a combinational materials design approach to the organosilica frameworks, pore wall surfaces and internal parts of mesopores has led to novel luminescent and photocatalytic systems. Their advanced functions have been realized by energy and electron transfer from framework organics to guest molecules or catalytic centers. PMOs, in which the precise design of hierarchical structures and construction of multi-component systems are practicable, have a significant future in a new field of functional materials (93 references).

Synthesis of a solid chelating ligand for the formation of efficient heterogeneous catalysts is highly desired in the fields of organic transformation and solar energy conversion. Here, we report the surfactant-directed self-assembly of a novel periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine (bpy) ligands within the framework (BPy-PMO) from a newly synthesized organosilane precursor [(i-PrO)3Si-C10H6N2-Si(Oi-Pr)3] without addition of any other silane precursors. BPy-PMO had a unique pore-wall structure in which bipyridine groups were densely and regularly packed and exposed on the surface. The high coordination ability to metals was also preserved. Various bipyridine-based metal complexes were prepared using BPy-PMO as a solid chelating ligand such as Ru(bpy)2(BPy-PMO), Ir(ppy)2(BPy-PMO) (ppy = 2-phenylpyridine), Ir(cod)(OMe)(BPy-PMO) (cod = 1,5-cyclooctadiene), Re(CO)3Cl(BPy-PMO), and Pd(OAc)2(BPy-PMO). BPy-PMO showed excellent ligand properties for heterogeneous Ir-catalyzed direct C-H borylation of arenes, resulting in superior activity, durability, and recyclability to the homogeneous analogous Ir catalyst. An efficient photocatalytic hydrogen evolution system was also constructed by integration of a Ru-complex as a photosensitizer and platinum as a catalyst on the pore surface of BPy-PMO without any electron relay molecules. These results demonstrate the great potential of BPy-PMO as a solid chelating ligand and a useful integration platform for construction of efficient molecular-based heterogeneous catalysis systems.

Light aqueduct: Periodic mesoporous organosilica exhibits strong light absorption due to densely packed organic chromophores within the pore walls. Light energy absorbed by 125 biphenyl groups in the pore walls is funneled into a single coumarin 1 molecule in the mesochannels with almost 100% quantum efficiency, and results in significant enhancement of emission from the coumarin 1 dye.

No abstract

No abstract

The aromatic excimers of benzene, naphthalene, anthracene, pyrene, and perylene are systematically investigated using the multiconfiguration quasi-degenerate perturbation theory (MCQDPT) method, which is one of high-level ab initio quantum chemical methods. The reference configuration space for MCQDPT is carefully designed for an appropriate description of the target electronic state with a tractable computational cost. The dimers with eclipsed parallel arrangement are investigated. The basis set dependence of the selected spectroscopic parameters is examined for the benzene and naphthalene dimers, and that of the excimer binding energy is found to be significant. In contrast, the equilibrium intermolecular distance and excimer fluorescence energy are less sensitive to the size of the basis sets used, and they agree with the corresponding experimental values, even with a nonextensive basis set size. The calculated spectroscopic parameters for anthracene, pyrene, and perylene dimers are also in good agreement with the experimental results. The electronic properties of the excimers are discussed in relation to those of the corresponding monomers. The wave functions of the excimers are analyzed in detail to clarify the origin of the attractive nature between the two monomers.

Various aromatic-bridged periodic mesoporous organosilica (PMO) thin films were prepared from 100% organosilane precursors containing bridging organics of 1,4-phenylene (Ph), 4,4′-biphenylylene (Bp), 2,6-naphthylene (Nph), and 9,10-anthrylene (Ant) by an evaporation-induced self-assembly approach. Structural and optical properties of the films were characterized. Transparent films with periodic mesostructures were successfully obtained for all the compositions. The absorption spectra of the PMO films were similar to those of their precursors, indicating little interaction between the aromatic groups in the frameworks in the ground state, whereas the fluorescence spectra of the PMO films significantly red-shifted and also broadened compared with those of their precursors, suggesting excimer formation in the excited state. The quantum yields of the Ph-, Nph-, and Ant-PMO films were lower than those of their precursors by solid-state quenching. Exceptionally, the quantum yield increased above that of the precursor for the Bp-PMO film in spite of excimer formation. The high absorption coefficient (87 000 cm -1 ) and high quantum yield (0.45) of the Bp-PMO film indicate its great potential for use as fluorescent materials. IntorductionPeriodic mesoporous organosilicas (PMOs), synthesized from 100% or less organic-bridged organosilane precursors [(R′O) 3 Si-R-Si(OR′) 3 ], are a new class of materials having well-defined nanoporous structure and framework functionalities attributed to organic groups in their pore walls. 1 PMOs have attracted much attention owing to their potential use in various applications such as catalysts, 2 adsorbents, 3 and optical devices. 4 PMOs are particularly suitable for optical applications in which a large amount of organic chromophores can be incorporated within their pore walls. PMOs containing a large amount of chromophores are expected to show a high absorption efficiency of light and unique optical properties due to the densely packed chromophores in their framework. Although several PMOs containing framework organic chromophores, such as viologen, 5 bispyridylethylene, 6 triphenylpyrylium, 7 Ru and Eu complexes, 4 and azobenzene 8 moieties, have been reported so far, these were prepared by co-condensation with a large amount of a pure silica precursor, such as tetraethoxysilane (82-99 mol %). The co-condensation approach resulted in dilution of the organic chromophores in the framework with silica. PMOs prepared from 100% bridged organosilane precursors have been reported for organic chromophores, such as phenylene, 9 biphenylylene, 10 thiophene, 11 diacetylene, 12 and carbazole. 13 However, optical properties of these PMOs have not been studied in detail.Especially for optical applications, transparent film-shaped PMOs 14,15 are advantageous compared with powder-shaped PMOs because of easy shaping (patterning) and low optical loss (no light scattering). Here, we focus on transparent filmshaped PMOs and synthesized PMO films from 100% organosilane precursors containing bridging organ...

This paper describes a new conceptual design for enhancement of photocatalytic CO(2) reduction of a rhenium(I) complex by light harvesting of periodic mesoporous organosilica (PMO). Mesoporous biphenyl-silica (Bp-PMO) anchoring fac-[Re(I)(bpy)(CO)(3)(PPh(3))](+)(OTf)(-) (bpy =2,2'-bipyridine; OTf = CF(3)SO(3)) in the mesochannels was synthesized by co-condensation of two organosilane precursors, 4,4'-bis(triethoxysilyl)biphenyl and 4-[4-{3-(trimethoxysilyl)propylsulfanyl}butyl]-4'-methyl-2,2'-bipyridine in the presence of a template surfactant, followed by coordination of a rhenium precursor, [Re(I)(CO)(5)(PPh(3))](+)(OTf)(-) to the bipyridine ligand in the mesochannels. The 280 nm light was effectively absorbed by the biphenyl groups in Bp-PMO, and the excited energy was funneled into the Re complex by resonance energy transfer, which enhanced photocatalytic CO evolution from CO(2) by a factor of 4.4 compared with direct excitation of the Re complex. Bp-PMO had an additional merit to protect the Re complex against a decomposition by UV irradiation. These results demonstrate the potential of PMOs as a light-harvesting antenna for designing various photoreaction systems, mimicking the natural photosynthesis.