An aqueous photocatalytic system exploits photophysical properties arising from the formation of supramolecular hydrogels, with properties and assembly modulated by the amino acids appended to an organic chromophore.
Two diketopyrrolopyrroles (DPPs) and three rylenes (NDI, dPyr PDI, and dEO PDI) were combined to form six hierarchical superstructures that assemble as a result of orthogonal H-bonding and π•••π stacking. The individual components and the DPP−NDI as well as DPP−PDI pairs were cast into films, and their superstructures were interrogated by electron microscopy and advanced spectroscopy. All six superstructures feature different geometries, causing subtle changes in the solid-state packing of the DPPs. Changes in inter-DPP stacking that are scaffolded by the adjacent rylenes have a subtle impact on both the excited-state dynamics and on activating new pathways such as singlet fission (SF). Our studies demonstrate the unique benefits of combinatorial supramolecular assembly in exploring the impact of structure on advanced light management in the form of SF to afford triplet quantum yields, which are as high as 65% for a correlated pair of triplets and 15% for an uncorrelated pair of triplets.
Microcrystal electron diffraction, grazing incidence wideangle scattering, and UV−vis spectroscopy were used to determine the unit-cell structure and the relative composition of dimethylated diketopyrrolopyrrole H-and J-polymorphs within thin films subjected to vapor solvent annealing (VSA) for different times. The electronic structure and excited-state deactivation pathways of the different polymorphs were examined by transient absorption spectroscopy, conductive probe atomic force microscopy, and molecular modeling. We find that VSA initially converts amorphous films into mixtures of H-and J-polymorphs and promotes further conversion from H to J with longer VSA times. Though both polymorphs exhibit efficient SF to form coupled triplets, free triplet yields are higher in J-polymorph films compared to mixed films because coupling in J-aggregates is lower and, in turn, more favorable for triplet decoupling.
Organic semiconductors have received substantial attention as active components in optoelectronic devices because of their processability and customizable properties.
We present the results of a computer simulation of the atomic structures of large-angle symmetrical tilt grain boundaries (GBs) Σ5 (misorientation angles 36.87 • and 53.13 • ), Σ13 (misorientation angles 22.62 • and 67.38 • ). The critical strain level ε crit criterion (phenomenological criterion) of Chisholm and Pennycook is applied to the computer simulation data to estimate the thickness of the nonsuperconducting layer h n enveloping the grain boundaries. The h n is estimated also by a bond-valence-sum analysis. We propose that the phenomenological criterion is caused by the change of the bond lengths and valence of atoms in the GB structure on the atomic level. The macro-and micro-approaches become consistent if the ε crit is greater than in earlier papers. It is predicted that the symmetrical tilt GB Σ5 θ = 53.13 • should demonstrate a largest critical current across the boundary. PACS: 74.50. +r; 61.72. Mm The major problem in the applications of YBa 2 Cu 3 O 7−δ (YBCO) crystals is their low critical current density J c caused by poor current transmission at the grain boundaries (GBs). The first studies of this phenomenon, starting with [1], showed that J c across the GBs decreases drastically with increasing misorientations angle θ between grains. Subsequent studies have indicated that certain specific large-angle GBs (near-Σ1 90 • [010] GBs) do not show this sharp decrease (for details see [2]). Several mechanisms have been suggested to explain the GBs influence on superconducting properties of YBCO (see for details [3,4]). We will examine the explanations based on the reduction of the order parameter caused by strain. Chisholm and Pennycook [5] suggested that cores of dislocations forming low-angle GB are nontransparent for the supercurrent because superconductivity is suppressed in the region of the crystal lattice where strains achieve some critical value ε crit . Based 1
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