| 1. |
- Gudeika, D., et al.
(författare)
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Flexible diphenylsulfone versus rigid dibenzothiophene-dioxide as acceptor moieties in donor-acceptor-donor TADF emitters for highly efficient OLEDs
- 2020
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 83
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Tidskriftsartikel (refereegranskat)abstract
- Flexible versus rigid molecular structures of donor-acceptor-donor type compounds are investigated with respect to efficiency of thermally activated delayed fluorescence (TADF) by theoretical and experimental approaches. Three highly efficient TADF emitters based on flexible diphenylsulfone and rigid dibenzothiophene-dioxide as acceptor units and di-tert-butyldimethyldihydroacridine as donor moiety were designed and synthesized. Despite they showed similar singlet-triplet splitting (0.01–0.02 eV) and high photoluminescence quantum yields in appropriate hosts, maximum external quantum efficiencies as different as 24.1 and 15.9/19.4% were obtained for organic light emitting devices based on these emitters with, respectively, flexible and rigid molecular structures. The high efficiency of the light-emitting compounds with the flexible molecular structure could be traced to the bi-configurational nature of the lowest singlet and triplet states resulting in higher spin-orbit coupling than for molecules with rigid structures. All derivatives showed bipolar charge transport character. High device efficiency with electron mobility of 3 × 10−5 cm2V−1s−1 and hole mobility of 1.3 × 10−4 cm2V−1s−1 at the electric field of 5 × 105 Vcm−1 was recorded for the layer of para-disubstituted diphenylsulfone with flexible molecular structure. This TADF emitter showed an excellent performance in the organic light emitting device, exhibiting a maximum current efficiency, power efficiency, and external quantum efficiency of 61.1 cdA-1, 64.0 lmW−1, and 24.1%, respectively.
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| 2. |
- Zhao, X., et al.
(författare)
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Persistent radical pairs trigger nano-gold to highly efficiently and highly selectively drive the value-added conversion of nitroaromatics
- 2021
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Ingår i: Chem Catalysis. - : Elsevier BV. - 2667-1107 .- 2667-1093. ; 1:5, s. 1118-1132
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Tidskriftsartikel (refereegranskat)abstract
- The development of advanced catalyst materials capable of efficiently capturing solar energy to drive the beneficial conversion of chemicals is a key part of the blueprint for “liquid sunlight.” Here, highly dispersed ultrafine nano-Au (B/TPTH3@Au) was anchored in situ on B/TPTH3 formed by alternate cross-linking of closo-[B12H12]2− and protonated 2,4,6-tris(4-pyridyl)-1,3,5-triazine. B/TPTH3@Au is an outstanding heterogeneous photocatalyst that converts low-value-added nitroaromatics into high-value-added azoaromatics. Compared with the slow kinetics of previous catalysts, the time required for the conversion of nitroaromatics to azoaromatics driven by B/TPTH3@Au is reduced by at least 10 times. These improvements could be derived from the synergy between the carrier B/TPTH3 (as a stable radical pair) and the nano-gold, including continuous electron transport in the functional carrier B/TPTH3 and the anchoring of highly dispersed ultrafine nano-Au with a strong localized surface plasmon resonance effect.
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| 3. |
- Opedal, Øystein H., et al.
(författare)
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Evolvability and trait function predict phenotypic divergence of plant populations
- 2023
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:1
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the causes and limits of population divergence in phenotypic traits is a fundamental aim of evolutionary biology, with the potential to yield predictions of adaptation to environmental change. Reciprocal transplant experiments and the evaluation of optimality models suggest that local adaptation is common but not universal, and some studies suggest that trait divergence is highly constrained by genetic variances and covariances of complex phenotypes. We analyze a large database of population divergence in plants and evaluate whether evolutionary divergence scales positively with standing genetic variation within populations (evolvability), as expected if genetic constraints are evolutionarily important. We further evaluate differences in divergence and evolvability- divergence relationships between reproductive and vegetative traits and between selfing, mixed-mating, and outcrossing species, as these factors are expected to influence both patterns of selection and evolutionary potentials. Evolutionary divergence scaled positively with evolvability. Furthermore, trait divergence was greater for vegetative traits than for floral (reproductive) traits, but largely independent of the mating system. Jointly, these factors explained -40% of the variance in evolutionary divergence. The consistency of the evolvability-divergence relationships across diverse species suggests substantial predictability of trait divergence. The results are also consistent with genetic constraints playing a role in evolutionary divergence.
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| 4. |
- Wu, H., et al.
(författare)
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Molecular phosphorescence in polymer matrix with reversible sensitivity
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:18, s. 20765-20774
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Tidskriftsartikel (refereegranskat)abstract
- Ultralong organic phosphorescence strongly depends on the formation of aggregation, while it is difficult to obtain in dilute environments on account of excessive internal and external molecular motions. Herein, ultralong single-molecule phosphorescence (USMP) at room temperature was achieved in the monomer state by coassembling biphenyl and naphthalene derivatives at low density with poly(vinyl alcohol) (PVA), where PVA provides a confined environment to stabilize the triplet state. Various factors that affect the USMP were studied, including aggregation, conformation, temperature, and moisture. In these systems, the formation of aggregates through intermolecular stacking and hydrogen bonding interactions in the film or crystal phases completely suppresses the USMP. However, the fluorescence is enhanced when coassembling these compounds at high concentration with PVA and becomes stronger in their powder state, indicating that the intersystem crossing process is blocked by the aggregation. Theoretical calculations suggest that the aggregation depresses spin-orbit coupling between the excited singlet and triplet states and enhances the nonradiative quenching process. Moreover, a relatively twisted conformation is more conducive to the occurrence of intersystem crossing than planar conformation. The USMP shows delicate and reversible sensitivity to the changes of temperature and moisture, rendering them with the applicability as smart organic optoelectronic materials.
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| 5. |
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| 6. |
- Ideböhn, Veronica, 1992, et al.
(författare)
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Symmetry breaking in core-valence double ionisation of allene
- 2023
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Ingår i: Communications Chemistry. - : Springer Nature. - 2399-3669. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Allene serves as a model to study multiple ionization of organic molecules. Here, the authors use synchrotron radiation-based multi-particle coincidence techniques and high-level ab initio calculations to propose a simple physical model to elucidate the symmetry breaking in core-valence double ionization of allene. Conventional electron spectroscopy is an established one-electron-at-the-time method for revealing the electronic structure and dynamics of either valence or inner shell ionized systems. By combining an electron-electron coincidence technique with the use of soft X-radiation we have measured a double ionisation spectrum of the allene molecule in which one electron is removed from a C1s core orbital and one from a valence orbital, well beyond Siegbahns Electron-Spectroscopy-for-Chemical-Analysis method. This core-valence double ionisation spectrum shows the effect of symmetry breaking in an extraordinary way, when the core electron is ejected from one of the two outer carbon atoms. To explain the spectrum we present a new theoretical approach combining the benefits of a full self-consistent field approach with those of perturbation methods and multi-configurational techniques, thus establishing a powerful tool to reveal molecular orbital symmetry breaking on such an organic molecule, going beyond Lowdins standard definition of electron correlation.
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| 7. |
- Kirschner, Johannes, et al.
(författare)
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The molecular structure of the surface of water-ethanol mixtures
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:19, s. 11568-11578
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of water and alcohol exhibit an excess surface concentration of alcohol as a result of the amphiphilic nature of the alcohol molecule, which has important consequences for the physico-chemical properties of water-alcohol mixtures. Here we use a combination of intensity vibrational sum-frequency generation (VSFG) spectroscopy, heterodyne-detected VSFG (HD-VSFG), and core-level photoelectron spectroscopy (PES) to investigate the molecular properties of water-ethanol mixtures at the air-liquid interface. We find that increasing the ethanol concentration up to a molar fraction (MF) of 0.1 leads to a steep increase of the surface density of the ethanol molecules, and an increased ordering of the ethanol molecules at the surface. When the ethanol concentration is further increased, the surface density of ethanol remains more or less constant, while the orientation of the ethanol molecules becomes increasingly disordered. The used techniques of PES and VSFG provide complementary information on the density and orientation of ethanol molecules at the surface of water, thus providing new information on the molecular-scale properties of the surface of water-alcohol mixtures over a wide range of compositions. This information is invaluable in understanding the chemical and physical properties of water-alcohol mixtures.
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| 8. |
- Koulentianos, Dimitris, 1987, et al.
(författare)
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Formation and relaxation of K-2 and K-2V double-core-hole states in n-butane
- 2022
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 157:4
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Tidskriftsartikel (refereegranskat)abstract
- Using a magnetic bottle multi-electron time-of-flight spectrometer in combination with synchrotron radiation, double-core-hole pre-edge and continuum states involving the K-shell of the carbon atoms in n-butane ( n-C4H10) have been identified, where the ejected core electron(s) and the emitted Auger electrons from the decay of such states have been detected in coincidence. An assignment of the main observed spectral features is based on the results of multi-configurational self-consistent field (MCSCF) calculations for the excitation energies and static exchange (STEX) calculations for energies and intensities. MCSCF results have been analyzed in terms of static and dynamic electron relaxation as well as electron correlation contributions to double-core-hole state ionization potentials. The analysis of applicability of the STEX method, which implements the one-particle picture toward the complete basis set limit, is motivated by the fact that it scales well toward large species. We find that combining the MCSCF and STEX techniques is a viable approach to analyze double-core-hole spectra.
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| 9. |
- Lousen, B., et al.
(författare)
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Compressing a Non-Planar Aromatic Heterocyclic [7]Helicene to a Planar Hetero[8]Circulene
- 2020
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 26:22, s. 4935-4940
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a synthetic approach where a non-planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro-hetero[7]helicene, which is partially a helicene and partially a circulene: it is non-planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π-conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post-functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm).
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| 10. |
- Mao, L., et al.
(författare)
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Introducing chenodeoxycholic acid coadsorbent and strong electron-withdrawing group in indoline dyes to design high-performance solar cells : A remarkable theoretical improvement
- 2021
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 9:17, s. 5800-5807
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Tidskriftsartikel (refereegranskat)abstract
- The addition of coadsorbents and the introduction of electron-withdrawing groups in dye sensitizers are considered feasible strategies for improving the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). However, facile and precise predictions of the influence of these two strategies on their photovoltaic properties, including PCE, are challenging. In this contribution, we studied a known D-A-π-A indoline dye WS-2 adsorbed on a TiO2 anode represented by a supercell model. The PCE of this dye was evaluated to be between 9.69% and 13.70%, depending on the supercell representation, compared with an experimental value of 8.55%. The PCE could be increased to 16.39% on a moderate supercell by adding chenodeoxycholic acid (CDCA) as a coadsorbent. Such an enhancement could be ascribed to the intermolecular interaction between WS-2 and CDCA, suppressing excessively high dye coverage and thereby resulting in a remarkable increase in the open-circuit voltage. Based on WS-2, a new molecule WS-2a was rationally designed by substituting the benzothiadiazole moiety of WS-2 with a stronger electron-withdrawing thienyl-diketopyrrolopyrrole group. Consequently, the maximum absorption band showed a large red-shift from 522 to 638 nm, broadening the spectral response into the near-infrared region. A higher PCE of 16.62% was obtained for WS-2a. Moreover, the coadsorption of WS-2a and CDCA onto the TiO2 supercell achieved the best photovoltaic efficiency with a value as high as 24.15%. Therefore, the present study quantitatively reveals the impact of the coadsorbent and electron-withdrawing groups on the optoelectronic properties of dyes, which opens a new avenue to design high-efficiency D-A-π-A-structured organic sensitizers for promising DSSC applications. A discussion on the qualification of these results is given.
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