Triptycene-Based Porous Metal-Assisted Salphen Organic Frameworks: Influence of the Metal Ions on Formation and Gas Sorption

Porous organic polymers (POPs) are chemically and thermally robust materials and have been often investigated for their gas sorption properties. From the related field of metal–organic frameworks (MOFs) it is known that open ligation sites at metal centers can enhance the performance of gas sorption significantly, especially the selectivity toward one gas of a binary mixture, such as CO₂/N₂ or CO₂/CH₄. POPs that contain metal centers are rarer. One possibility to introduce metals into POPs is by the synthesis of metal-assisted salphen organic frameworks (MaSOFs), where the framework development is associated with the formation of the metal–salphen pockets. Based on a hexakissalicylaldehyde, a variety of three-dimensional isostructural porous MaSOFs with different metal ions (Zn²⁺, Ni²⁺, Cu²⁺, Pd²⁺, and Pt²⁺) are introduced. All compounds show a very similar pore structure and comparable specific surface areas, which make these MaSOFs ideal candidates to study the influence of the nature of the incorporated metal center on gas sorption selectivity. Due to the environmental importance, the adsorption of CO₂ in comparison to N₂ and CH₄ was extensively studied. Depending on the metal ions, the heat of adsorption was different as well as the Henry and IAST selectivities. Cu–MaSOF₁₀₀ for instance shows a high <i>Q</i>_st of 31.2 kJ mol^–1 for CO₂ and an uptake of 14.9 wt % at 1 bar and 273 K. The IAST selectivity of CO₂/N₂ for an 80/20 mixture is with <i>S</i>_IAST = 52 very high for a metal containing POP and even comparable to some of the best performing MOFs. The MaSOFs are stable even in boiling water. This, as well as the simple synthesis, makes them potential good candidates for CO₂ removal of binary mixtures

Triptycene-Based Porous Metal-Assisted Salphen Organic Frameworks: Influence of the Metal Ions on Formation and Gas Sorption

Porous organic polymers (POPs) are chemically and thermally robust materials and have been often investigated for their gas sorption properties. From the related field of metal–organic frameworks (MOFs) it is known that open ligation sites at metal centers can enhance the performance of gas sorption significantly, especially the selectivity toward one gas of a binary mixture, such as CO₂/N₂ or CO₂/CH₄. POPs that contain metal centers are rarer. One possibility to introduce metals into POPs is by the synthesis of metal-assisted salphen organic frameworks (MaSOFs), where the framework development is associated with the formation of the metal–salphen pockets. Based on a hexakissalicylaldehyde, a variety of three-dimensional isostructural porous MaSOFs with different metal ions (Zn²⁺, Ni²⁺, Cu²⁺, Pd²⁺, and Pt²⁺) are introduced. All compounds show a very similar pore structure and comparable specific surface areas, which make these MaSOFs ideal candidates to study the influence of the nature of the incorporated metal center on gas sorption selectivity. Due to the environmental importance, the adsorption of CO₂ in comparison to N₂ and CH₄ was extensively studied. Depending on the metal ions, the heat of adsorption was different as well as the Henry and IAST selectivities. Cu–MaSOF₁₀₀ for instance shows a high <i>Q</i>_st of 31.2 kJ mol^–1 for CO₂ and an uptake of 14.9 wt % at 1 bar and 273 K. The IAST selectivity of CO₂/N₂ for an 80/20 mixture is with <i>S</i>_IAST = 52 very high for a metal containing POP and even comparable to some of the best performing MOFs. The MaSOFs are stable even in boiling water. This, as well as the simple synthesis, makes them potential good candidates for CO₂ removal of binary mixtures

Solid-State Gels of Poly(<i>p</i>‑phenyleneethynylene)s by Solvent Exchange

Solutions of dialkoxy- and dialkyl-poly­(<i>p</i>-phenyleneethynylene)­s (PPE) form well-defined solid state gels by diffusion of a nonsolvent (SOG), even if the concentration of the PPEs is only 2.5 mg/mL. The residual solvent in the SOG gel does not contain any dissolved PPE according to fluorescence and emissive lifetime measurements. The solvent inside of the gels is confirmed to be more than 90% of the polar solvent, which gives temperature stability to the gel and makes it available for infiltration of analytes, etc. This is in strong contrast to “classic” gels that form by thermal gelation; these still contain dissolved PPE chains. As a result, an ionic-liquid-filled PPE gel could be formed successfully by solvent exchange

A Tetraphenylethene-Based Polymer Array Discriminates Nitroarenes

Four tetraphenylethene (TPE)-based aryleneethynylene-type polymers (<b>TPEPs</b>) are reported in this work. All of them show aggregate-induced emission (AIE). Their optical properties have been investigated. The <b>TPEPs</b> are tested as a sensor array for 14 different nitroaromatic analytes and display fingerprint fluorescence quenching responses. The <b>TPEPs</b> demonstrate good sensitivity and discriminatory power in detecting explosives. The quenching efficiencies are dependent on the spectral overlap areas (absorbance of the analyte and the emission of the fluorescent polymer) and on the LUMO level of the analytes. The specific quenching responses are recorded and visualized after processing the data by linear discriminant analysis (LDA). Fourteen nitroarenes are discriminated by the four-element sensor array. Even five pairs of regioisomeric nitroarenes with similar physical and chemical properties were easily discriminated

Truxene-Based Hyperbranched Conjugated Polymers: Fluorescent Micelles Detect Explosives in Water

We report two hyperbranched conjugated polymers (HCP) with truxene units as core and 1,4-didodecyl-2,5-diethynylbenzene as well as 1,4-bis­(dodecyloxy)-2,5-diethynylbenzene as comonomers. Two analogous poly­(<i>para</i>-phenyleneethynylene)­s (PPE) are also prepared as comparison to demonstrate the difference between the truxene and the phenyl moieties in their optical properties and their sensing performance. The four polymers are tested for nitroaromatic analytes and display different fluorescence quenching responses. The quenching efficiencies are dependent upon the spectral overlap between the absorbance of the analyte and the emission of the fluorescent polymer. Optical fingerprints are obtained, based on the unique response patterns of the analytes toward the polymers. With this small sensor array, one can distinguish nine nitroaromatic analytes with 100% accuracy. The amphiphilic polymer F127 (a polyethylene glycol–polypropylene glycol block copolymer) carries the hydrophobic HCPs and self-assembles into micelles in water, forming highly fluorescent HCP micelles. The micelle-bound conjugated polymers detect nitroaromatic analytes effectively in water and show an increased sensitivity compared to the sensing of nitroaromatics in organic solvents. The nitroarenes are also discriminated in water using this four-element chemical tongue

Interplay of Interfacial Layers and Blend Composition To Reduce Thermal Degradation of Polymer Solar Cells at High Temperature

The thermal stability of printed polymer solar cells at elevated temperatures needs to be improved to achieve high-throughput fabrication including annealing steps as well as long-term stability. During device processing, thermal annealing impacts both the organic photoactive layer, and the two interfacial layers make detailed studies of degradation mechanism delicate. A recently identified thermally stable poly­[[4,8-bis­[(2-ethylhexyl)­oxy]­benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene-2,6-diyl]­[3-fluoro-2-[(2-ethylhexyl)­carbonyl]­thieno­[3,4-<i>b</i>]­thiophenediyl]]:[6,6]-phenyl-C₇₁-butyric acid methyl ester (PTB7:PC₇₀BM) blend as photoactive layer in combination with poly­(3,4-ethylenedioxythiophene) polystyrene sulfonate as hole extraction layer is used here to focus on the impact of electron extraction layer (EEL) on the thermal stability of solar cells. Solar cells processed with densely packed ZnO nanoparticle layers still show 92% of the initial efficiency after constant annealing during 1 day at 140 °C, whereas partially covering ZnO layers as well as an evaporated calcium layer leads to performance losses of up to 30%. This demonstrates that the nature and morphology of EELs highly influence the thermal stability of the device. We extend our study to thermally unstable PTB7:[6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM) blends to highlight the impact of ZnO on the device degradation during annealing. Importantly, only 12% loss in photocurrent density is observed after annealing at 140 °C during 1 day when using closely packed ZnO. This is in stark contrast to literature and addressed here to the use of a stable double-sided confinement during thermal annealing. The underlying mechanism of the inhibition of photocurrent losses is revealed by electron microscopy imaging and spatially resolved spectroscopy. We found that the double-sided confinement suppresses extensive fullerene diffusion during the annealing step, but with still an increase in size and distance of the enriched donor and acceptor domains inside the photoactive layer by an average factor of 5. The later result in combination with comparably small photocurrent density losses indicates the existence of an efficient transport of minority charge carriers inside the donor and acceptor enriched phases in PTB7:PC₆₀BM blends

Unraveling the Nanoscale Morphologies of Mesoporous Perovskite Solar Cells and Their Correlation to Device Performance

Hybrid solar cells based on organometal halide perovskite absorbers have recently emerged as promising class for cost- and energy-efficient photovoltaics. So far, unraveling the morphology of the different materials within the nanostructured absorber layer has not been accomplished. Here, we present the first visualization of the mesoporous absorber layer in a perovskite solar cell from analytical transmission electron microscopy studies. Material contrast is achieved by electron spectroscopic imaging. We found that infiltration of the hole transport material into the scaffold is low and inhomogeneous. Furthermore, our data suggest that the device performance is strongly affected by the morphology of the TiO₂ scaffold with a fine grained structure being disadvantageous