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...