Synthesis and characterization of the optical properties of mesostructured and mesoporous materials.

摘要

Currently, there is considerable effort to produce compact solid state lasers, waveguides, switches, and sensors. In order to achieve the optimal devices, it will be necessary to simultaneously control multiple length scales with molecular precision. The acid catalyzed synthesis and evaporation induced co-self-assembly of active species/silica/block-copolymer nanocomposites to produce ordered mesostructured materials is emerging as one possible technology to achieve these devices. By selectively controlling the isoelectric point of the silica precursors, the thermodynamics and kinetics of competing molecular assembly interactions can be effectively controlled to produce defined structures from the nanometer to the centimeter length scale. Further, the mesoscopic integration of the block-copolymer and silica components yields structures that combine the mechanical strength of the inorganic framework together with the desirable processing and solubility properties of the organic polymer.; The optical properties of dye-doped mesostructured (inorganic/surfactant composites) and dye-grafted mesoporous (inorganic/air) materials were investigated. It was found that the simultaneous co-assembly leads to improvements in optical characteristics by allowing high doping concentrations while at the same time maintaining high dye dispersion to avoid concentration quenching. This advantage was utilized to fabricate extremely stable photochromic materials that change their color upon irradiation with the fastest switching kinetics of any solid state matrix. The structural confinement resulting from the selective inorganic/organic phase separation was then explored to produce a dual laser dye composite that undergoes highly efficient energy transfer. The ease of processing was used to fabricate arrays of distributed feedback (DFB) lasers using elastomeric stamps to pattern dye-doped mesostructured silica into ridge waveguides with a grating on top. Their versatility of dopants was examined by incorporating up to 0.2 wt% of the conjugated polymer MEH-PPV and it was found to enhance its quantum efficiency compared to the neat conjugated polymer films. Finally, optical pH sensors were produced by in-situ functionalization of fluorescein molecules to mesostructured silica thin films. Subsequent low-temperature polymer extraction produced optically clear mesoporous thin films that displayed very fast response times.