| 11. |
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| 12. |
- HUDNER, J, et al.
(författare)
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PREPARATION OF YBA2CU3O7-X FILMS AND YBA2CU3O7-X/Y2O3 MULTILAYERS USING COEVAPORATION AND ATOMIC OXYGEN
- 1993
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 73, s. 3096-3098
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Tidskriftsartikel (refereegranskat)abstract
- Thin layers of YBa2Cu3O7-x (YBCO) deposited on LaAlO3 substrates have been prepared in situ by coevaporation of Y, Ba, and Cu. Incorporation of oxygen was accomplished by an atomic oxygen beam source with high cracking efficiency. The total oxygen flow at the substrate could be kept low enough to permit the use of a quadrupole mass spectrometer for evaporation rate monitoring. Films were strongly c-axis oriented with rocking curve full width at half-maximum values of 0.6-degrees. Transport measurements on patterned films yielded critical current densities of 6 x 10(6) A/cm2 at 77 K. The deposition method was demonstrated to be feasible for preparation of Y2O3/YBCO heterostructures.
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| 13. |
- Kato, H., et al.
(författare)
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Z/E-photoisomerizations of olefins with 4nπ- or (4n + 2)π-electron substituents: Zigzag variations in olefin properties along the T1 state energy surfaces
- 2005
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 70:23, s. 9495-9504
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Tidskriftsartikel (refereegranskat)abstract
- A quantum chemical study has been performed to assess changes in aromaticity along the T1 state Z/E-isomerization pathways of annulenyl-substituted olefins. It is argued that the point on the T1 energy surface with highest substituent aromaticity corresponds to the minimum. According to Baird (J. Am. Chem. Soc. 1972, 94, 4941), aromaticity and antiaromaticity are interchanged when going from S0 to T1. Thus, olefins with S0 aromatic substituents (set A olefins) will be partially antiaromatic in T1 and vice versa for olefins with S 0 antiaromatic substituents (set B olefins). Twist of the C=C bond to a structure with a perpendicular orientation of the 2p(C) Orbitals ( 3p*) in T1 should lead to regaining substituent aromaticity in set A and loss of aromaticity in set B olefins. This hypothesis is verified through quantum chemical calculations of T1 energies, geometries (bond lengths and harmonic oscillator measure of aromaticity), spin densities, and nucleus independent chemical shifts whose differences along the T1 PES display zigzag dependencies on the number of π-electrons in the annulenyl substituent of the olefin. Aromaticity changes are reflected in the profiles of the T1 potential energy surfaces (T1 PESs) for Z/E-isomerizations because olefins in set A have minima at 3p* whereas those in set B have maxima at such structures. The proper combination (fusion) of the substituents of set A and B olefins could allow for design of novel optical switch compounds that isomerize adiabatically with high isomerization quantum yields.
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| 14. |
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| 15. |
- Lofas, H., et al.
(författare)
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A computational study of potential molecular switches that exploit Baird's rule on excited-state aromaticity and antiaromaticity
- 2014
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 174, s. 105-124
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Tidskriftsartikel (refereegranskat)abstract
- A series of tentative single-molecule conductance switches which could be triggered by light were examined by computational means using density functional theory (DFT) with non-equilibrium Green's functions (NEGF). The switches exploit the reversal in electron counting rules for aromaticity and antiaromaticity upon excitation from the electronic ground state (S-0) to the lowest pi pi* excited singlet and triplet states (S-1 or T-1), as described by Wicket's and Baird's rules, respectively. Four different switches and one antifuse were designed which rely on various photoreactions that either lead from the OFF to the ON states (switches 1, 2 and 4, and antifuse 5) or from the ON to the OFF state (switch 3). The highest and lowest ideal calculated switching ratios are 1175 and 5, respectively, observed for switches 1 and 4. Increased thermal stability of the 1-ON isomer is achieved by benzannulation (switch 1B-OFF/ON). The effects of constrained electrode-electrode distances on activation energies for thermal hydrogen back-transfer from 1-ON to 1-OFF and the relative energies of 1-ON and 1-OFF at constrained geometries were also studied. The switching ratio is strongly distance-dependent as revealed for 1B-ON/OFF where it equals 711 and 148 when the ON and OFF isomers are calculated in electrode gaps with distances confined to either that of the OFF isomer or to that of the ON isomer, respectively.
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| 16. |
- Mphahlele M.J, Fernandes M.A, El-Nahas A.M, Ottosson H, Ndlovu S.M, Sithole H.M, Dladla B.S, De Waal D.
(författare)
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Solution Phase, Solid State and Computational Structural Studies of 2-Aryl-3-bromoquinolin-4(1H)-one Derivatives
- 2002
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Ingår i: J. Chem. Soc., Perkins Trans. 2. ; , s. 2159-2164
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Shoji, Y., et al.
(författare)
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An Element-Substituted Cyclobutadiene Exhibiting High-Energy Blue Phosphorescence
- 2021
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Ingår i: Angewandte Chemie International Edition. - : John Wiley and Sons Inc. - 1433-7851 .- 1521-3773. ; 60:40, s. 21817-21823
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Tidskriftsartikel (refereegranskat)abstract
- 1,3,2,4-Diazadiboretidine, an isoelectronic heteroanalogue of cyclobutadiene, is an interesting chemical species in terms of comparison with the carbon system, whereas its properties have never been investigated experimentally. According to Baird's rule, Hückel antiaromatic cyclobutadiene acquires aromaticity in the lowest triplet state. Here we report experimental and theoretical studies on the ground- and excited-state antiaromaticity/aromaticity as well as the photophysical properties of an isolable 1,3,2,4-diazadiboretidine derivative. The crystal structure of the diazadiboretidine derivative revealed that the B2N2 ring adopts a planar rhombic geometry in the ground state. Yet, theoretical calculations showed that the B2N2 ring turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the diazadiboretidine derivative has the lowest singlet and triplet states lying at close energy levels and displays blue phosphorescence.
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