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991.
Ilaria Ciofini Dr. Carlo Adamo Prof. Dr. Yoshio Teki Prof. Dr. Fabien Tuyèras Dr. Philippe P. Lainé Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(36):11385-11405
Ground‐state (GS) and excited‐state (ES) properties of novel photomagnetic molecular devices (PMMDs) are investigated by means of density functional theory. These organic PMMDs undergo a ferromagnetic alignment of their intramolecular spins in the lowest ES. They are comprised of: 1) an anthracene unit (An) as both the photosensitizer (P) and a transient spin carrier (SC) in the triplet ES (3An*); 2) imino‐nitroxyl (IN) or oxoverdazyl (OV) stable radical(s) as the dangling SC(s); and 3) bridge(s) (B) connecting peripheral SC(s) to the An core at positions 9 and 10. Improving the efficiency of the PMMDs involves strengthening the ES intramolecular exchange coupling (JES) between transient and persistent SCs, hence the choice of 2‐pyrimidinyl (pm) as B elements to replace the original p‐phenylene (ph). Dissymmetry of the pm connectors leads to [SC‐B‐P‐B‐SC] regio‐isomers int. and ext., depending on whether the pyrimidinic nitrogen atoms point towards the An core or the peripheral SCs, respectively. For the int. regio‐isomers we show that the photoinduced spin alignment is significantly improved because the JES/kB value is increased by a factor of more than two compared with the ph‐based analogue (JES/kB>+400 K). Most importantly, we show that the optimal JES/kB value (≈+600 K) could be reached in the event of an unexpected saddle‐shaped structural distortion of the lowest ES. Accounting for this intriguing behavior requires dissection of the combined effects of 1) borderline intramolecular steric hindrance about key An–pm linkages, which translates into the flatness of the potential energy surface; 2) spin density disruption due to the presence of radicals; and 3) possibly intervening photochemistry, with An acting as a light‐triggered electron donor while pm, IN, and OV behave as electron acceptors. Finally, potentialities attached to the [(SC)‐pm‐An‐pm]int pattern are disclosed. 相似文献
992.
Hisashi Shimakoshi Yusuke Iseki Chihaya Adachi Yoshio Hisaeda 《Tetrahedron letters》2008,49(43):6198-6201
Porphycene was covalently immobilized in a sol-gel silica film deposited on a glass plate, and the immobilized porphycene showed a photosensitizing property with recycling for the photo-oxidation of 1,5-dihydroxynaphthalene. 相似文献
993.
Ochiai M Yoshimura A Mori T Nishi Y Hirobe M 《Journal of the American Chemical Society》2008,130(12):3742-3743
Reported here for the first time are the oxidative couplings of alkynes and primary alcohols yielding conjugated enones. Although the BF3-catalyzed reaction of terminal alkynes with p-trifluoromethylphenyl(difluoro)-lambda3-bromane results in the fluoro-lambda3-bromanation of triple bonds to afford (E)-beta-fluorovinyl-lambda3-bromanes, reaction of an alkyne with the difluoro-lambda3-bromane in the presence of an alcohol and BF3-Et2O affords directly conjugated enones in good yields. The reaction proceeds in a highly stereo- and regioselective manner under metal-free conditions. Interestingly, no formation of enones was detected, when difluoro-lambda3-iodane p-CF3C6H4IF2 was used instead of the lambda3-bromane. A mechanism involving a lambda3-bromane-induced oxidation of an alcohol to an aldehyde, [2 + 2] cyclization with alkynes yielding 2H-oxetes, and finally the electrocyclic ring opening is discussed. 相似文献
994.
Yamaguchi Y Matsubara Y Ochi T Wakamiya T Yoshida Z 《Journal of the American Chemical Society》2008,130(42):13867-13869
How the pi conjugation length affects the fluorescence emission efficiency is elucidated by examination of the theoretical and experimental relationship between absolute quantum yield (Phi(f)) and magnitude (Api) of the pi conjugation length in the excited singlet state, which provides a novel concept for molecular design for highly fluorescent organic compounds. As a tool to predict Phi(f) from a structural model, (nu(a) - nu(f))1/2 x a3/2 (nu(a): wavenumber of absorption maximum, nu(f): wavenumber of emission maximum, a: molecular radius) could be used instead of Api. The concept should be valuable for potential applications to (1) examination of an excited singlet state structure (for example, coplanarity of excited-state molecules) and (2) molecular design of novel materials, in which the excited singlet state plays an important role, such as highly efficient fluorophores, electroluminescent materials, photoconducting materials, and nonlinear optical materials. A remarkably intense green fluorophore (Phi(f) 0.88, log epsilon 4.72, lambda(em) 527 nm) is created based on this concept, which is of great interest in relation to a green fluorescent protein (Topaz, T203Y type, Phi(f) 0.60, log epsilon 4.98, lambda(em) 527 nm). 相似文献
995.
Yamaguchi Y Shimoi Y Ochi T Wakamiya T Matsubara Y Yoshida Z 《The journal of physical chemistry. A》2008,112(23):5074-5084
To create highly fluorescent organic compounds in longer wavelength regions, and to gain physical chemistry insight into the photophysical characteristics, we investigated photophysical properties (Phi(f), lambda(em), tau, lambda(abs), epsilon, k(r), and k(d)) and their controlling factor dependence of the following pi-conjugated molecular rods consisting of p-phenyleneethynylene units modified by donor (OMe) and/or acceptor (CN): (1) side-donor modification systems (SD systems), (2) side-acceptor modification systems (SA systems), and (3) systems consisting of donor block and acceptor block (BL systems). As a result, very high Phi(f) values (>0.95) were obtained for BL systems. Bathochromic shifts of lambd(em) in the same pi conjugation length were largest for BL systems. Thus we succeeded in the creation of highly efficient light emitters in the longer wavelength region by block modification (e.g., Phi(f) = 0.97, lambda(em) = 464 nm for BL-9), contrary to expectation from energy gap law. Considerably intense solid emission (Phi(f) approximately 0.5) in the longer wavelength region (500-560 nm) was also found for BL systems, presumably because of molecular orientation that hinders the self-quenching of fluorescence in solids. From (1) a Lippert-Mataga plot, (2) density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, and (3) the positive linear relationship between the optical transition energy (nu(em)) and the difference between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor (HOMO(D)-LUMO(A) difference), it is elucidated that the excited singlet (S1) state of BL systems has a high charge transfer nature. The number (n) of energetically equivalent dipolar structure (EEDS) units in the oligoarylene ethynylenes is shown to be a measure of the effective pi conjugation length in the S1 state. The S1 state planarity increases with n values of EEDS units and by the introduction of donor and/or acceptor groups. It is worth noting that the Phi(f) values increase linearly with the n values of EEDS units. 相似文献
996.
997.
We have investigated ultrasound-assisted synthesis of guanidine derivatives using 1H-Pyrazole-1-carboxamidine (PyzCA) and S-substituted isothiouronium sulfate (MeITU). The guanylations of several amines are promoted by ultrasound sonication under solvent-free conditions, and proceed under mild conditions. It is of particular interest that the guanylations do not require bases in most cases. 相似文献
998.
Hidetsura Cho Yoshio Nishimura Hiroshi Ikeda Mitsuhiro Asakura Shinji Toyota 《Tetrahedron》2018,74(20):2405-2413
Experimental and theoretical studies on the thermodynamics and properties of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates were undertaken by 1H NMR measurements and DFT (density functional theory) calculations. The ratios of tautomers a/b of dihydropyrimidines (DPs) 1, 2, and 3 were determined under various conditions to reveal the effects of temperature, solvent, and concentration on the thermodynamic data. The observed results, the free energy differences (ΔG), enthalpy differences (ΔH), and entropy differences (ΔS), are discussed in terms of the molecular structures, dipole moments (DM), and the electrostatic potential maps calculated by the DFT to clarify the nature of the DPs. 相似文献
999.
1000.
Hirotaka Kushida Miwako Fukutake Masahiro Tabuchi Takao Katsuhara Hiroaki Nishimura Yasushi Ikarashi Masanao Kanitani Yoshio Kase 《Biomedical chromatography : BMC》2013,27(12):1647-1656
Uncaria Hook (UH) alkaloids are involved in the beneficial effects of Yokukansan. However, the pharmacokinetics of UH alkaloids after oral administration of Yokukansan has not yet been sufficiently investigated. Therefore, we developed and validated a sensitive and specific high‐performance liquid chromatography with tandem mass spectrometry (LC/MS/MS) method for the simultaneous quantitation of seven UH alkaloids (corynoxeine, isocorynoxeine, rhynchophylline, isorhynchophylline, hirsutine, hirsuteine and geissoschizine methyl ether) in rat plasma and brain. After protein precipitation with acetonitrile, chromatographic separation was performed using an Ascentis Express RP‐amide column, with gradient elution with 0.2% formic acid and acetonitrile at 0.3 mL/min. All analytes in the plasma and brain showed good linearity over a wide concentration range (r > 0.995). Intra‐day and inter‐day variations of each constituent were 8.6 and 8.0% or less in the plasma, and 14.9 and 15.0% or less in the brain, respectively. The validated LC/MS/MS method was applied in the pharmacokinetic studies of UH alkaloids after oral administration of Yokukansan to rats. In the plasma, rhynchophylline, hirsutine, hirsuteine and geissoschizine methyl ether were detected, but only geissoschizine methyl ether was detected in the brain. These results suggest that geissoschizine methyl ether is an important constituent of the pharmacological effects of Yokukansan. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献