Quadruple Stack Research Articles

Engineering Soluble Diketopyrrolopyrrole Chromophore Stacks from a Series of Pd(II)-Based Ravels.

A strategy to engineer the stacking of diketopyrrolopyrrole (DPP) dyes based on non-statistical metallosupramolecular self-assembly is introduced. For this, the DPP backbone is equipped with nitrogen-based donors that allow for different discrete assemblies to be formed upon the addition of Pd(II), distinguished by the number of π-stacked chromophores. A Pd3 L6 three-ring, a heteroleptic Pd2 L2 L'2 ravel composed of two crossing DPPs (flanked by two carbazoles), and two unprecedented self-penetrated motifs (a Pd2 L3 triple and a Pd2 L4 quadruple stack), were obtained and systematically investigated. With increasing counts of stacked chromophores, UV/Vis absorptions red-shift and emission intensities decrease, except for compound Pd2 L2 L'2 , which stands out with an exceptional photoluminescence quantum yield of 51 %. This is extraordinary for open-shell metal containing assemblies and explainable by an intra-assembly FRET process. The modular design and synthesis of soluble multi-chromophore building blocks offers the potential for the preparation of nanodevices and materials with applications in sensing, photo-redox catalysis and optics.

Pd(II)‐vermittelte Assemblierung einer Reihe von löslichen Diketopyrrolopyrrol‐Chromophor‐Stapeln**

AbstractEs wird eine Strategie zur Stapelung von Diketopyrrolopyrrol‐Farbstoffen (DPP) vorgestellt, die auf einem nicht‐statistischen Ansatz zur metallosupramolekularen Selbstassemblierung beruht. Dazu wird das DPP‐Grundgerüst mit stickstoffbasierten Donoren ausgestattet, die bei Zugabe von Pd(II) Kationen die Bildung verschiedener diskreter Strukturen ermöglichen, welche sich durch die Anzahl der π‐gestapelten Chromophore unterscheiden. Ein Pd3L6‐Dreiring, eine heteroleptische Pd2L2L′2‐Anordnung, bestehend aus zwei sich kreuzenden DPPs (flankiert von zwei Carbazolen), und zwei bisher unbeschriebene, sich selbst durchdringende Motive (ein Pd2L3‐Dreifach‐ und ein Pd2L4‐Vierfachstapel) wurden erhalten und systematisch untersucht. Mit zunehmender Anzahl gestapelter Chromophore kommt es zu einer Rotverschiebung der UV/Vis‐Absorption und einer Abnahme der Emissionsintensität, mit Ausnahme der Verbindung Pd2L2L′2, die eine außergewöhnlich hohe Photolumineszenz‐Quantenausbeute von 51 % aufweist. Dies ist unüblich für Verbindungen, die offenschalige Metallionen enthalten, und lässt sich durch einen intramolekularen FRET‐Prozess erklären. Das modulare Design solcher löslicher Multi‐Chromophor‐Bausteine eröffnet Möglichkeiten für die Herstellung von Nanobauteilen und ‐materialien mit Anwendungen in den Bereichen Sensorik, Photo‐Redox‐Katalyse und Optik.

LWSNet - a novel deep-learning architecture to segregate Covid-19 and pneumonia from x-ray imagery.

Automatic detection of lung diseases using AI-based tools became very much necessary to handle the huge number of cases occurring across the globe and support the doctors. This paper proposed a novel deep learning architecture named LWSNet (Light Weight Stacking Network) to separate Covid-19, cold pneumonia, and normal chest x-ray images. This framework is based on single, double, triple, and quadruple stack mechanisms to address the above-mentioned tri-class problem. In this framework, a truncated version of standard deep learning models and a lightweight CNN model was considered to conviniently deploy in resource-constraint devices. An evaluation was conducted on three publicly available datasets alongwith their combination. We received 97.28%, 96.50%, 97.41%, and 98.54% highest classification accuracies using quadruple stack. On further investigation, we found, using LWSNet, the average accuracy got improved from individual model to quadruple model by 2.31%, 2.55%, 2.88%, and 2.26% on four respective datasets.

Supramolecular p/n‐heterojunction of C60‐functionalized bis(merocyanine) quadruple stack: A model system for charge carrier separation and recombination in organic solar cells

AbstractSupramolecular photosystems can afford important insights into elementary processes in molecular materials. Here, a bis(merocyanine)‐C60 conjugate composed of two covalently tethered electron‐donating merocyanine chromophores and two appended fullerene electron acceptor units is investigated. Concentration‐dependent UV/Vis studies in nonpolar solvents revealed a bimolecular association (dimerization) process, resulting in the formation of an H‐coupled merocyanine dye aggregate. The aggregate structure was confirmed by 2D NMR spectroscopy proving the presence of a well‐defined quadruple dye stack surrounded by four loosely connected fullerenes, which mimics the donor–acceptor interface in bulk heterojunction (BHJ) solar cells. Due to the interdigitation of the dyes in the quadruple stack motif, even at low concentrations, fully aggregated species prevail in nonpolar solvents, which enabled us to elucidate the photophysics of this supramolecular p/n‐heterojunction in dilute solution by femtosecond time‐resolved transient absorption spectroscopy. The observed photophysical processes include a favorably fast photoinduced electron transfer from the electron‐donating dye stack to the electron‐accepting fullerene moieties, a slower geminate charge carrier recombination of the generated electron and hole in the supramolecular p/n‐heterojunction as well as the formation of fullerene triplet states. While the geminate recombination of charge carriers is supposed to be less competitive in BHJ photovoltaic materials due to the possibility of fast electron migration within fullerene domains in thin films, intersystem crossing into the triplet manifold appears as a more critical undesired process. These insights from spectroscopy may help to tailor improved photovoltaic materials, thereby demonstrating the value of fundamental studies on elementary photophysical processes in molecular aggregates.KEY POINTS Supramolecular p/n‐heterojunction by self‐assembly in solution Aggregate structure confirmed by NMR spectroscopy Photoinduced electron transfer studied by transient absorption spectroscopy

Discrete Supramolecular Stacks Based on Multinuclear Tweezer-Type Rhodium Complexes.

By taking advantage of self-complementary π-π stacking and CH-π interactions, a series of discrete quadruple stacks were constructed through the self-aggregation of U-shaped dirhodium metallotweezer complexes featuring various planar polyaromatic ligands. By altering the conjugate stacking strength and bridging ligands, assemblies with a range of topologies were obtained, including a binuclear D-shaped macrocycle, tetranuclear open-ended cagelike frameworks, and duplex metallotweezer stacking structures. Furthermore, a rare stacking interaction resulting in selective C-H activation was observed during the self-assembly process of these elaborate architectures.

Essential States Model for Merocyanine Dye Stacks: Bridging Electronic and Optical Absorption Properties

An extension of the essential states model is developed to investigate the absorption and electronic properties of a highly dipolar merocyanine dye and double and quadruple π-stacks formed upon the folding and self-assembly of appropriate spacer-tethered bis(merocyanine) dyes. Our analysis reveals that a simple two-state model is not sufficient to adequately describe the absorption features of a single chromophore. However, by including an additional bridge state, the absorption features are well described and reasonable values for the permanent and transition dipole moments are obtained. We show that the low-energy absorption band of the folded double stack results from vibronic coupling, whereas the additional absorption shoulder observed in the spectrum of the self-assembled quadruple stack is due to a transition to a lower excited state. Furthermore, the chromophores within both π-stacks exhibit an increase in the charge-transfer character in the ground state with respect to the single chromophore arising from polarizability effects, which are not accounted for in the conventional Frenkel exciton theory. These insights are of significant importance for the proper design of functional materials based on merocyanines and dipolar chromophores in general.

Ultrafast Exciton Delocalization, Localization, and Excimer Formation Dynamics in a Highly Defined Perylene Bisimide Quadruple π-Stack.

An adequately designed, bay-tethered perylene bisimide (PBI) dimer Bis-PBI was synthesized by Pd/Cu-catalyzed Glaser-type oxidative homocoupling of the respective PBI building block. This newly synthesized PBI dimer self-assembles exclusively and with high binding constants of up to 106 M-1 into a discrete π-stack of four chromophores. Steady-state absorption and emission spectra show the signatures of H-type excitonic coupling among the dye units. Broadband fluorescence upconversion spectroscopy (FLUPS) reveals an ultrafast dynamics in the optically excited state. An initially coherent Frenkel exciton state that is delocalized over the whole quadruple stack rapidly (τ = ∼200 fs) loses its coherence and relaxes into an excimer state. Comparison with Frenkel exciton dynamics in PBI dimeric and oligomeric H-aggregates demonstrates that in the quadruple stack coherent exciton propagation is absent due to its short length of aggregates, thereby it has only one relaxation pathway to the excimer state. Furthermore, the absence of pump-power dependence in transient absorption experiments suggests that multiexciton cannot be generated in the quadruple stack, which is in line with time-resolved fluorescence measurements.

A continuous read-out TPC for the ALICE upgrade

The largest gaseous Time Projection Chamber (TPC) in the world, the ALICE TPC, will be upgraded based on Micro Pattern Gas Detector technology during the second long shutdown of the CERN Large Hadron Collider in 2018/19. The upgraded detector will operate continuously without the use of a triggered gating grid. It will thus be able to read all minimum bias Pb–Pb events that the LHC will deliver at the anticipated peak interaction rate of 50kHz for the high luminosity heavy-ion era. New read-out electronics will send the continuous data stream to a new online farm at rates up to 1TByte/s.A fractional ion feedback of below 1% is required to keep distortions due to space charge in the TPC drift volume at a tolerable level. The new read-out chambers will consist of quadruple stacks of Gas Electron Multipliers (GEM), combining GEM foils with a different hole pitch. Other key requirements such as energy resolution and operational stability have to be met as well. A careful optimisation of the performance in terms of all these parameters was achieved during an extensive R&D program. A working point well within the design specifications was identified with an ion backflow of 0.63%, a local energy resolution of 11.3% (sigma) and a discharge probability comparable to that of standard triple GEM detectors.

Discrete Double‐to‐Quadruple Aromatic Stacks: Stepwise Integration of Face‐to‐Face Geometries in Cocrystals Based on Indolocarbazole

One, two, three, four: An indolocarbazole organizes double, triple, and quadruple stacks of aromatic molecules within multicomponent solids. The aromatic units are sequentially integrated into discrete assemblies and undergo [2+2] photodimerization.

Kinetic analysis of the role of the tyrosine 13, phenylalanine 56 and glutamine 54 network in the U1A/U1 hairpin II interaction

The A protein of the U1 small nuclear ribonucleoprotein particle, interacting with its stem–loop RNA target (U1hpII), is frequently used as a paradigm for RNA binding by recognition motif domains (RRMs). U1A/U1hpII complex formation has been proposed to consist of at least two steps: electrostatically mediated alignment of both molecules followed by locking into place, based on the establishment of close-range interactions. The sequence of events between alignment and locking remains obscure. Here we examine the roles of three critical residues, Tyr13, Phe56 and Gln54, in complex formation and stability using Biacore. Our mutational and kinetic data suggest that Tyr13 plays a more important role than Phe56 in complex formation. Mutational analysis of Gln54, combined with molecular dynamics studies, points to Arg52 as another key residue in association. Based on our data and previous structural and modeling studies, we propose that electrostatic alignment of the molecules is followed by hydrogen bond formation between the RNA and Arg52, and the sequential establishment of interactions with loop bases (including Tyr13). A quadruple stack, sandwiching two bases between Phe56 and Asp92, would occur last and coincide with the rearrangement of a C-terminal helix that partially occludes the RRM surface in the free protein.

Extended Surface Heat Transfer

Extended Surface Heat Transfer