排序方式: 共有55条查询结果,搜索用时 15 毫秒
51.
Kim YH Jeong DH Kim D Jeoung SC Cho HS Kim SK Aratani N Osuka A 《Journal of the American Chemical Society》2001,123(1):76-86
The molecular design of directly meso-meso-linked porphyrin arrays as a new model of light-harvesting antenna as well as a molecular photonic wire was envisaged to bring the porphyrin units closer for rapid energy transfer. For this purpose, zinc(II) 5,15-bis(3,5-bis(octyloxy)phenyl)porphyrin (Z1) and its directly meso-meso-linked porphyrin arrays up to Z128 (Zn, n represents the number of porphyrins) were synthesized. The absorption spectra of these porphyrin arrays change in a systematic manner with an increase in the number of porphyrins; the high-energy Soret bands remain at nearly the same wavelength (413-414 nm), while the low-energy exciton split Soret bands are gradually red-shifted, resulting in a progressive increase in the exciton splitting energy. The exciton splitting is nicely correlated with the values of cos[pi/(N + 1)] according to Kasha's exciton coupling theory, providing a value of 4250 cm(-1) for the exciton coupling energy in the S(2) state. The increasing red-shifts for the Q-bands are rather modest. The fluorescence excitation anisotropy spectra of the porphyrin arrays show that the photoexcitation of the high-energy Soret bands exhibits a large angle difference between absorption and emission dipoles in contrast with the photoexcitation of the low-energy exciton split Soret and Q-bands. This result indicates that the high-energy Soret bands are characteristic of the summation of the individual monomeric transitions with its overall dipole moment deviated from the array chain direction, while the low-energy Soret bands result from the exciton splitting between the monomeric transition dipoles in line with the array chain direction. From the fluorescence quantum yields and fluorescence lifetime measurements, the radiative coherent length was estimated to be 6-8 porphyrin units in the porphyrin arrays. Ultrafast fluorescence decay measurements show that the S(2) --> S(1) internal conversion process occurs in less than 1 ps in the porphyrin arrays due to the existence of exciton split band as a ladder-type deactivation channel, while this process is relatively slow in Z1 (approximately 1.6 ps). The rate of this process seems to follow the energy gap law, which is mainly determined by the energy gap between the two Soret bands of the porphyrin arrays. 相似文献
52.
Doo-Hua Choi Jun-Ho Lee Hyun-Cheol Kim Han-Byeol Lee Nae Bong Jeoung Do-Hyun Park Hakseong Kim Sung Ho Jhang Sang-Wook Lee Hyun-Jong Chung 《Current Applied Physics》2017,17(1):11-14
We have investigated the performances of barristors with a graphene-tungsten disulfide (WS2) junction by varying the thickness of WS2 and gate oxide. On-current density (JON) and on- and off-current ratio (JON/JOFF) increases, and sub-threshold swing (VSS) decreases with the WS2 thickness. Also, barristors with thicker WS2 required less workfunction shift, to switch the barristors. Therefore, unlike the traditional devices, VSS of barristor with gate dielectric 300 nm was smaller than that of 90 nm, when the former is fabricated with thicker WS2 than the latter. Since materials properties of 2-dimensional semiconductors generally vary with their thickness, the thickness of 2D semiconductors could become a key parameter to engineer the performance of barristors with graphene and the 2D semiconductors. 相似文献
53.
Diaminopyridine (DAP) functionalized POSS derivatives self-assemble on thymine functionalized monolayers on gold surfaces affording hybrid inorganic/organic surfaces. 相似文献
54.
Terahertz electromagnetic wave transmission through random arrays of single rectangular holes and slits in thin metallic sheets 总被引:1,自引:0,他引:1
We report on the observation of terahertz transparency in random arrays of the single rectangular holes and slits with the areal coverage of only 12%. The terahertz transparency occurs at the fundamental shape resonance of the rectangular holes and confirms the theoretical predictions of earlier works of García-Vidal et al. [Phys. Rev. Lett. 95, 103901 (2005)] on single rectangular holes and of Ruan and Qiu [Phys. Rev. Lett. 96, 233901 (2006)] on random arrays of holes. 相似文献
55.
Yudhajeet Basak Dr. Jae-Hun Jeoung Dr. Lilith Domnik Prof. Dr. Holger Dobbek 《Angewandte Chemie (International ed. in English)》2023,62(32):e202305341
Ni,Fe-containing carbon monoxide dehydrogenases (CODHs) catalyze the reversible reduction of carbon dioxide to carbon monoxide. CODHs are found in anaerobic microorganisms and can rapidly lose their activity when exposed to air. What causes the loss of activity is unclear. In this study, we analyzed the time-dependent structural changes induced by the presence of air on the metal centers of CODH-II. We show that inactivation is a multistep process. In a reversible step, the open coordination site on the Ni ion is blocked by a Ni,Fe-bridging μ-sulfido or chlorido ligand. Blocking this open coordination site with a cyanide ligand stabilizes the cluster against O2-induced decomposition, indicating that O2 attacks at the Ni ion. In the subsequent irreversible phase, nickel is lost, the Fe ions rearrange and the sulfido ligands disappear. Our data are consistent with a reversible reductive reactivation mechanism to protect CODHs from transient over-oxidation. 相似文献