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991.
Jiang He Florian Rauch Dr. Alexandra Friedrich Dr. Daniel Sieh Dr. Tatjana Ribbeck Dr. Ivo Krummenacher Prof. Dr. Holger Braunschweig Prof. Dr. Maik Finze Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13777-13784
N-heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor (D)–π–A compounds 1 – 3 . In addition, an enamine π-donor analogue ( 4 ) was synthesized for comparison. UV–visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of cyclic (alkyl)(amino) carbenes (CAACs). Solvent-dependent emission studies indicate that 1 – 4 have moderate intramolecular charge-transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3 , =−0.40 V vs. ferrocene/ferrocenium, Fc/Fc+, in THF). Time-dependent (TD) DFT calculations show that the HOMOs of 1 – 3 are much more destabilized than that of the enamine-containing 4 , which confirms the stronger donating ability of NHOs. 相似文献
992.
The effect of terminal groups of oligomer electrolytes on the photovoltaic performance of dye-sensitized solar cells (DSSCs) have been systematically investigated to show that the terminal group plays a critical role in determining the concentration of I(3)(-), ionic conductivity, flatband potential and consequently the energy conversion efficiency. 相似文献
993.
ShiGuoSUN XiaoJunPENG MingWenFAN YongQianXU LeiSHI LiChengSU 《中国化学快报》2004,15(8):965-968
Two novel rhenium(I) 2, 2′-bipyridyl complexes, [(4,4′-di-COOEt-bipy) Re(CO)3 (NCCH3)PF6] and [(4,4′-di-COOEt-bipy) Re (CO)3 (NCS)], a model complex [(4,4′-di-COOEt-bipy) Re (CO)3 (pyridine)PF6], were synthesized. Their ground state electronic spectra and emission spectra were measured in acetonitrile. The MLCT absorption maximum of the complex exhibited a considerable red shift as the ligand changed from pyridine to CNCH3, or SCN. 相似文献
994.
995.
Dr. Guglielmo Monaco Prof. Emeritus Lawrence T. Scott Prof. Riccardo Zanasi 《ChemistryOpen》2020,9(5):616-622
The three-fold HOMO-LUMO gap oscillation, typical of finite length armchair carbon nanotubes (CNT), has a major effect on the magnetic response of ultrashort, single-end-capped [5,5] carbon nanotubes to a perturbing magnetic field parallel to the main symmetry axis. For the CNT's containing 40, 70, and 100 carbon atoms, for which 100 % of the C=C double bonds can be grouped into aromatic-sextets, i. e., fully or complete Clar networks, large paratropic (antiaromatic) global circulations around the cylindrical axis are predicted at the DFT level of calculation. Local and semi-global diatropic (aromatic) currents of strengths not larger than that of the benzene molecule are determined for a perpendicular perturbing magnetic field. CNTs of intermediate lengths do not display this enhanced antiaromatic response. The paratropic current flow clearly shows that these complete Clar networks can be viewed as stacked cycloparaphenylene belts, each providing a double annulene circuit as a consequence of the quinoidal resonance structure that results from their closure. Paradoxically, the fully aromatic Clar structure itself is responsible for the enhanced global antiaromaticity. 相似文献
996.
Miklos Kertesz Yong S. Lee James J. P. Stewart 《International journal of quantum chemistry》1989,35(2):305-313
It is shown that infinite long polyacene chains may have three energetically close but structurally distinct isomers (a symmetrical, sym, form and two lower symmetry forms: one with double bonds in a trans and another isomer with double bonds in a cis pattern). The energetics is based on solid state MNDO theory. We discuss that the symmetrical form has a substantial energy gap Eg in the Hartree–Fock approach owing to exact exchange terms, which are nonlocal. Broken symmetry Hartree–Fock (HF ) solutions for polyacene are also described. An angularly distorted structure suggested earlier on Jahn–Teller grounds is found to be energetically not favorable. 相似文献
997.
998.
Ying-nan Xuan Yan Gao Yong Huang Xi-gao Jian Laboratory of Cellulose Lignocellulosics Chemistry Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Institute of Chemistry Chinese Academy of Sciences Beijing China Department of Polymer Science College of Chemical Engineering Dalian University of Technology Dalian China 《高分子科学》2002,(3):225-229
A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K_2CO_3 to produce high molecular weight polymers which can be dissolved in some polarsolvents such as chloroform and nitrobenzene at room temperature and can be easily can into flexible, yellowish andtransparent films. PPESK is an amorphous polymer having a decomposition temperature above 400℃, which indicates that ithas high thermal stability. At the same time, the thermal properties of PPESKs with dicyandiamide (DICY) as curing agentindicated that the heat-resistance properties of the PPESKs are improved after curing. The apparent activation energy (ΔE) ofthe cross-linking reaction and the reaction order (n) of PPESK/DICY were found to be 52.2 kJ/mol and ca. 1.0, respectively.Therefore, the cross-linking reaction is approximately a first order reaction. 相似文献
999.
I. A. Mostert P. Anker H. -B. Jenny U. Oesch W. E. Morf D. Ammann Prof. Dr. W. Simon 《Mikrochimica acta》1985,85(1-2):33-38
Summary Silicone rubber is a universal membrane matrix for neutral carrier based ion-selective electrodes. Carrier antibiotics as well as synthetic ionophores yield sensors with selectivities that are comparable or even higher than those of corresponding poly(vinyl chloride) (PVC) membrane systems. The permeability of silicone rubber membranes for gas molecules is about ten times higher than the permeability of PVC membranes. In contrast, the electrical conductivity is by a factor of 10–100 lower.
Auf neutralen Carriern beruhende Silikongummimembran-Elektroden mit Selektivität für H3O+, K+, NH4 + und Ca2+
Zusammenfassung In ionenselektiven Elektroden auf der Basis von neutralen Carriern läßt sich Silikongummi als universelle Membranmatrix einsetzen. Entsprechende Sensoren sind sowohl mit ionenselektiven Antibiotika als auch mit synthetischen Carriern realisiert worden. Ihre Selektivitäten übertreffen teilweise jene von entsprechenden PVC-Membranen. Die Permeabilität der Silikongummimembranen für Gasmolekel ist ungefähr zehnmal höher als jene von PVC-Membranen. Andererseits ist die elektrische Leitfähigkeit um einen Faktor 10–100 niedriger.相似文献
1000.
Theoretical study on structures and stability of C4P isomers 总被引:1,自引:0,他引:1
The structures, energetics, spectroscopies, and stabilities of doublet C(4)P isomeric species are explored at the DFT/B3LYP, QCISD, and CCSD(T) (singlet-point) levels. A total of 12 minimum isomers and 27 interconversion transition states are located. At the CCSD(T)/6-311G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest-lying isomer is a floppy CCCCP 1 (0.0 kcal/mol) mainly featuring a cumulenic structure |C=C=C=C=P*|, which differs much from the analogous C4N radical (|*C-C[triple bond]C-C[triple bond]N|). The quasi-linearity and the low bending mode of 1 are in contrast to the previous prediction. The second energetically followed isomer PC-cCCC 3 (14.9 kcal/mol) possesses a CCC ring-bonded to CP. The two low-lying isomers are separated by a high-energy ring-closure/open transition state (26.5 kcal/mol) and thus are very promising candidates for future laboratory and astrophysical detection. Furthermore, four high-energy isomers, that is, two bent isomers CCPCC 2 (68.4 kcal/mol) and CCPCC 2' (68.5 kcal/mol) and two cagelike species 10 (56.0 kcal/mol) and 11 (67.9 kcal/mol), are also stabilized by considerable barriers. The present work is the first detailed potential energy survey of CnP clusters and can provide useful information for the investigation of larger CnP radicals and for understanding the isomerism of P-doped C vaporization processes. 相似文献