Expression of proteins of interest in food

PòsterJun

Macroscopic Domains within an Oriented TQ1 Film Visualized Using 2D Polarization Imaging

Large-area self-assembly of functional conjugated polymers holds a great potential for practical applications of organic electronic devices. We obtained well-aligned films of poly­[2,3-bis­(3-octyloxyphenyl)­quinoxaline-5,8-diyl-<i>alt</i>-thiophene-2,5-diyl] (TQ1) using the floating film transfer method. Thereby, a droplet of the TQ1 solution was injected on top of the surface of an immiscible liquid substrate, at the meniscus formed at the edge of a Petri dish, from where the polymer solution and the film spread in one direction. Characterization of the TQ1 film using the recently developed two-dimensional polarization imaging (2D POLIM) revealed large, millimeter-sized domains of oriented polymer chains. The irregular shape of the contact line at the droplet source induced the appearance of disordered stripes perpendicular to the spreading direction. A correlation of polarization parameters measured using 2D POLIM revealed the microstructure of such stripes, providing valuable information for further improvement and possible upscaling of this promising method

Macroscopic Domains within an Oriented TQ1 Film Visualized Using 2D Polarization Imaging

Large-area self-assembly of functional conjugated polymers holds a great potential for practical applications of organic electronic devices. We obtained well-aligned films of poly­[2,3-bis­(3-octyloxyphenyl)­quinoxaline-5,8-diyl-<i>alt</i>-thiophene-2,5-diyl] (TQ1) using the floating film transfer method. Thereby, a droplet of the TQ1 solution was injected on top of the surface of an immiscible liquid substrate, at the meniscus formed at the edge of a Petri dish, from where the polymer solution and the film spread in one direction. Characterization of the TQ1 film using the recently developed two-dimensional polarization imaging (2D POLIM) revealed large, millimeter-sized domains of oriented polymer chains. The irregular shape of the contact line at the droplet source induced the appearance of disordered stripes perpendicular to the spreading direction. A correlation of polarization parameters measured using 2D POLIM revealed the microstructure of such stripes, providing valuable information for further improvement and possible upscaling of this promising method

Effect of Conjugated Backbone Protection on Intrinsic and Light-Induced Fluorescence Quenching in Polythiophenes

Polythiophenes (PTs), particularly regioregular poly­(3-hexylthiophene-2,5-diyl) (rr-P3HT), are important materials in photovoltaics. The photophysical properties of PTs are still poorly understood, because of their aggregation tendency and formation of interchain species which can be avoided by insulating the conjugated backbone via self-threading. We investigated two polymers, rr-P3HT and its insulated analog, imbedded in PMMA at low concentrations. The exciton decay dynamics and fluorescence quantum yield were analyzed as a function of excitation power densities over the range from 1 × 10^–4 to 100 W/cm². For both polymers, substantial (up to 5 times) photoinduced fluorescence quenching was observed owing to singlet–triplet annihilation and quenching by other long-living charged photoproducts. We found that chain insulation eliminates static (or ultrafast) fluorescence quenching, but has no effect on slow dynamic quenching at time scales longer than 10 ps. We propose that static quenching is solely due to chain aggregation, whereas the dynamic quenching is a consequence of intrachain processes

Super-Resolution Luminescence Microspectroscopy Reveals the Mechanism of Photoinduced Degradation in CH₃NH₃PbI₃ Perovskite Nanocrystals

Photoinduced degradation of individual methylammonium lead triiodide (MAPbI₃) perovskite nanocrystals was studied using super-resolution luminescence microspectroscopy under intense light excitation. The photoluminescence (PL) intensity decrease and blue-shift of the PL spectrum up to 60 nm together with spatial shifts in the emission localization position up to a few hundred nanometers were visualized in real time. PL blinking was found to temporarily suspend the degradation process, indicating that the degradation needs a high concentration of mobile photogenerated charges to occur. We propose that the mechanistic process of degradation occurs as the three-dimensional MAPbI₃ crystal structure smoothly collapses to the two-dimensional layered PbI₂ structure. The degradation starts locally and then spreads over the whole crystal. The structural collapse is primarily due to migration of methylammonium ions (MA⁺), which distorts the lattice structure causing alterations to the Pb–I–Pb bond angle and in turn changes the effective band gap

Super-Resolution Luminescence Microspectroscopy Reveals the Mechanism of Photoinduced Degradation in CH₃NH₃PbI₃ Perovskite Nanocrystals

Photoinduced degradation of individual methylammonium lead triiodide (MAPbI₃) perovskite nanocrystals was studied using super-resolution luminescence microspectroscopy under intense light excitation. The photoluminescence (PL) intensity decrease and blue-shift of the PL spectrum up to 60 nm together with spatial shifts in the emission localization position up to a few hundred nanometers were visualized in real time. PL blinking was found to temporarily suspend the degradation process, indicating that the degradation needs a high concentration of mobile photogenerated charges to occur. We propose that the mechanistic process of degradation occurs as the three-dimensional MAPbI₃ crystal structure smoothly collapses to the two-dimensional layered PbI₂ structure. The degradation starts locally and then spreads over the whole crystal. The structural collapse is primarily due to migration of methylammonium ions (MA⁺), which distorts the lattice structure causing alterations to the Pb–I–Pb bond angle and in turn changes the effective band gap

Organization of Bacteriochlorophylls in Individual Chlorosomes from Chlorobaculum tepidum Studied by 2-Dimensional Polarization Fluorescence Microscopy

Chlorosomes are the largest and most efficient natural light-harvesting systems and contain supramolecular assemblies of bacteriochlorophylls that are organized without proteins. Despite a recent structure determination for chlorosomes from Chlorobaculum tepidum (Ganapathy Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525), the issue of a possible large structural disorder is still discussed controversially. We have studied individual chlorosomes prepared under very carefully controlled growth condition by a novel 2-dimensional polarization single molecule imaging technique giving polarization information for both fluorescence excitation and emission simultaneously. Contrary to the existing literature data, the polarization degree or modulation depth (<i>M</i>) for both excitation (absorption) and emission (fluorescence) showed extremely narrow distributions. The fluorescence was always highly polarized with <i>M</i> ≈ 0.77, independent of the excitation wavelength. Moreover, the fluorescence spectra of individual chlorosomes were identical within the error limits. These results lead us to conclude that all chlorosomes possess the same type of internal organization in terms of the arrangement of the bacteriochlorophyll c transition dipole moments and their total excitonic transition dipole possess a cylindrical symmetry in agreement with the previously suggested concentric multitubular chlorophyll aggregate organization (Ganapathy Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525<i>)</i>

Single Lévy States–Disorder Induced Energy Funnels in Molecular Aggregates

Using fluorescence super-resolution microscopy we studied simultaneous spectral, spatial localization, and blinking behavior of individual 1D J-aggregates. Excitons migrating 100 nm are funneled to a trap appearing as an additional red-shifted blinking fluorescence band. We propose that the trap is a Frenkel exciton state formed much below the main exciton band edge due to an environmentally induced heavy-tailed Lévy disorder. This points to disorder engineering as a new avenue in controlling light-harvesting in molecular ensemble

Polarization Imaging of Emissive Charge Transfer States in Polymer/Fullerene Blends

Photoexcitation of conjugated polymer–fullerene blends results in population of a local charge transfer (CT) state at the interface between the two materials. The competition between recombination and dissociation of this interfacial state limits the generation of fully separated free charges. Therefore, a detailed understanding of the CT states is critical for building a comprehensive picture of the organic solar cells operation. We applied a new fluorescence microscopy method called two-dimensional polarization imaging to gain insight into the orientation of the transition dipole moments of the CT states, and the associated excitation energy transfer processes in TQ1:PCBM blend films. The polymer phase was oriented mechanically to relate the polymer dipole moment orientation to that of the CT states. CT state formation was observed to be much faster than energy transfer in the polymer phase. However, after being formed an emissive CT state does not exchange excitation energy with other CT states, suggesting that they are spatially and/or energetically isolated. We found that the quantum yield of the CT emission is smaller for CT states spatially located in the highly oriented polymer domains, which is interpreted as the result of enhanced CT state dissociation in highly ordered structures

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