Talented Mesoporous Silica Nanoparticles

The structure and functionality of mesoporous silica nanoparticles can be tuned by means of numerous and diverse synthetic strategies. Focusing on experimental methods, we describe how pore size and pore topology of the mesopore system can be modified through templating and pore-swelling agents, as well as different synthesis conditions. Moreover, we show how the mesoporous nanoparticles can be functionalized through co-condensation methods with silane coupling agents, with specific emphasis on the spatially selective anchoring of different molecular functionalities within the nanoparticles. We discuss methods for changing the composition of the pore walls of the mesoporous particles, for example by including redox-sensitive sulfide bonds or by creating autofluorescent curcumin-containing mesoporous organosilica. The efficiency of targeted drug delivery applications strongly depends on morphological parameters such as size and shape of the mesoporous nanoparticles. It is demonstrated how the particle size of the mesoporous nanoparticles can be modified over a wide range from about 30 nm to several hundred nanometers. Developing this context further, we consider several examples of triggered molecular mechanisms intended for the controlled intracellular release of bioactive substances from the pore system of mesoporous nanoparticles

Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on–off control of the translational movement of the molecules

Spectrally Switchable Photodetection with Near-Infrared-Absorbing Covalent Organic Frameworks

Most covalent organic frameworks (COFs) to date are made from relatively small aromatic subunits, which can only absorb the high-energy part of the visible spectrum. We have developed near-infrared-absorbing low bandgap COFs by incorporating donor–acceptor-type isoindigo- and thieno­isoindigo-based building blocks. The new materials are intensely colored solids with a high degree of long-range order and a pseudo-quadratic pore geometry. Growing the COF as a vertically oriented thin film allows for the construction of an ordered interdigitated heterojunction through infiltration with a complementary semiconductor. Applying a thieno­isoindigo-COF:fullerene heterojunction as the photoactive component, we realized the first COF-based UV- to NIR-responsive photodetector. We found that the spectral response of the device is reversibly switchable between blue- and red-sensitive, and green- and NIR-responsive. To the best of our knowledge, this is the first time that such nearly complete inversion of spectral sensitivity of a photodetector has been achieved. This effect could lead to potential applications in information technology or spectral imaging

Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on–off control of the translational movement of the molecules

Stabilization of the Trigonal High-Temperature Phase of Formamidinium Lead Iodide

Formamidinium lead iodide (FAPbI₃) has the potential to achieve higher performance than established perovskite solar cells like methylammonium lead iodide (MAPbI₃), while maintaining a higher stability. The major drawback for the latter material is that it can crystallize at room temperature in a wide bandgap hexagonal symmetry (<i>P</i>6₃<i>mc</i>) instead of the desired trigonal (<i>P</i>3<i>m</i>1) black phase formed at a higher temperature (130 °C). Our results show that employing a mixture of MAI and FAI in films deposited via a two-step approach, where the MAI content is <20%, results in the exchange of FA molecules with MA without any significant lattice shrinkage. Additionally, we show with temperature-dependent X-ray diffraction that the trigonal phase exhibits no phase changes in the temperature range studied (25 to 250 °C). We attribute the stabilization of the structure to stronger interactions between the MA cation and the inorganic cage. Finally, we show that the inclusion of this small amount of MA also has a positive effect on the lifetime of the photoexcited species and results in more efficient devices

Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on–off control of the translational movement of the molecules

Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on–off control of the translational movement of the molecules

Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on–off control of the translational movement of the molecules

Guided in Situ Polymerization of MEH-PPV in Mesoporous Titania Photoanodes

Incorporation of conjugated polymers into porous metal oxide networks is a challenging task, which is being pursued via many different approaches. We have developed the guided in situ polymerization of poly­(2-methoxy-5-(2′-ethylhexyloxy)-<i>p</i>-phenylenevinylene) (MEH-PPV) in porous titania films by means of surface functionalization. The controlled polymerization via the Gilch route was induced by an alkoxide base and by increasing the temperature. The selected and specially designed surface-functionalizing linker molecules mimic the monomer or its activated form, respectively. In this way, we drastically enhanced the amount of MEH-PPV incorporated into the porous titania phase compared to nonfunctionalized samples by a factor of 6. Additionally, photovoltaic measurements were performed. The devices show shunting or series resistance limitations, depending on the surface functionalization prior to in situ polymerization of MEH-PPV. We suggest that the reason for this behavior can be found in the orientation of the grown polymer chains with respect to the titania surface. Therefore, the geometry of the anchoring via the linker molecules is relevant for exploiting the full electronic potential of the conjugated polymer in the resulting hybrid composite. This observation will help to design future synthesis methods for new hybrid materials from conjugated polymers and n-type semiconductors to take full advantage of favorable electronic interactions between the two phases

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A novel synthesis method for large-pore, well-aligned 2D hexagonal mesoporous silica thin films is reported. The alignment was achieved by confinement in poly(dimethylsiloxane) (PDMS) microgrooves without the necessity of additional forces (such as electric fields). We describe the influence of various experimental conditions including the way the grooves are filled, surface modification at the solid/liquid interfaces, and the height-to-width ratio of the microgrooves on mesopore alignment. With this technique, highly oriented mesoporous silica channels can be obtained at a length scale of several millimeters. For a nondestructive, detailed, and wide-ranging structural and dynamic characterization of the as-synthesized mesochannel silica network, dye molecules were incorporated into the channels at concentrations suitable for single-molecule microscopy. A “maximum projection” of individual frames recorded with a fluorescence microscope immediately gives a global overview (“map”) of the pore structure, thus providing direct feedback for tuning synthesis conditions. In addition, deeper insights into the real nanoscale structure of the mesoporous silica framework were obtained through high-accuracy single-molecule tracking experiments. The high spatial accuracy of the experiments allowed for the direct observation of jumps of single dye molecules between individual channels in the mesoporous silica host. Nevertheless, due to the low concentration of defects, the diffusion could be described as a 1D random walk where the molecules diffuse along the highly oriented, parallel channels and sometimes switch from channel to channel through small defects in the pore walls. Furthermore, it could be shown with single-molecule microscopy that template removal and calcination of the aligned films results in an increased defect concentration; however, the overall order of the structures remained intact