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71.
72.
Yong Ni Dr. Tullimilli Y. Gopalakrishna Dr. Hoa Phan Dr. Tun Seng Herng Shaofei Wu Yi Han Prof. Jun Ding Prof. Jishan Wu 《Angewandte Chemie (International ed. in English)》2018,57(31):9697-9701
Peri‐acenes are good model compounds for zigzag graphene nanoribbons, but their synthesis is extremely challenging owing to their intrinsic open‐shell diradical character. Now, the successful synthesis and isolation of a stable peri‐tetracene derivative PT‐2ClPh is reported; four 2,6‐dichlorophenyl groups are attached onto the most reactive sites along the zigzag edges. The structure was confirmed by X‐ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It exhibits an open‐shell singlet ground state with a moderate diradical character (y0=51.5 % by calculation) and a small singlet–triplet gap (ΔES‐T=?2.5 kcal mol?1 by SQUID measurement). It displays global aromatic character, which is different from the smaller‐size bisanthene analogue BA‐CF3 . 相似文献
73.
Single-molecule spectroscopic investigation of energy migration processes in cyclic porphyrin arrays
Park M Yoon MC Yoon ZS Hori T Peng X Aratani N Hotta J Uji-I H Sliwa M Hofkens J Osuka A Kim D 《Journal of the American Chemical Society》2007,129(12):3539-3544
Covalently linked cyclic porphyrin arrays have been synthesized to mimic natural light-harvesting apparatuses and to investigate the highly efficient energy migration processes occurring in these systems for future applications in molecular photonics. To avoid an ensemble-averaged picture, we performed a single-molecule spectroscopic study on the energy migration processes of cyclic porphyrin arrays and a linear model compound embedded in a rigid polymer matrix by recording fluorescence intensity trajectories, by performing coincidence measurements, and by doing wide-field defocused imaging. Our study demonstrates efficient energy migration within the cyclic porphyrin arrays at the single-molecule level. By comparison with the data of the linear model compound, we could pinpoint the role of the dipole-dipole coupling between diporphyrin subunits and the rigidity of the cyclic structures on the energy transfer processes. 相似文献
74.
Isha A Yusof NA Ahmad M Suhendra D Yunus WM Zainal Z 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(5):1398-1402
Fatty hydroxamic acid (FHA) immobilized in polyvinyl chloride (PVC) has been studied as a sensor element of an optical fibre chemical sensor for V(V). By using this instrument, V(V) in solution has been determined in the log concentration range of 0-2.5 (i.e. 1.0-300 mg/L). The detection limit was 1.0 mg/L. The relative standard deviation (R.S.D.) of the method for the reproducibility study at V(V) concentration of 200 mg/L and 300 mg/L were calculated to be 2.9% and 2.0%, respectively. Interference from foreign ions was also studied at 1:1 mole ratio of V(V):foreign ions. It was found that, Fe(III) ion interfered most in the determination of vanadium(V). Excellent agreement with ICP-AES method was achieved when the proposed method was applied towards determination of V(V). 相似文献
75.
76.
Zhe Zhang Qixia Bai Erendra Manandhar Yunting Zeng Tun Wu Ming Wang Liao-Yuan Yao George R. Newkome Pingshan Wang Ting-Zheng Xie 《Chemical science》2022,13(20):5999
Beyond the AIE (aggregation-induced emission) phenomenon in small molecules, supramolecules with AIE properties have evolved in the AIE family and accelerated the growth of supramolecular application diversity. Inspired by its mechanism, particularly the RIV (restriction of intramolecular vibrations) process, a feasible strategy of constructing an AIE-supramolecular cage based on the oxidation of sulfur atoms and coordination of metals is presented. In contrast to previous strategies that used molecular stacking to limit molecular vibrations, we achieved the desired goal using the synergistic effects of coordination-driven self-assembly and oxidation. Upon assembling with zinc ions, S1 was endowed with a distinct AIE property compared with its ligand L1, while S2 exhibited a remarkable fluorescence enhancement compared to L2. Also, the single cage-sized nanowire structure of supramolecules was obtained via directional electrostatic interactions with multiple anions and rigid-shaped cationic cages. Moreover, the adducts of zinc porphyrin and supramolecules were investigated and characterized by 2D DOSY, ESI-MS, TWIM-MS, UV-vis, and fluorescence spectroscopy. The protocol described here enriches the ongoing research on tunable fluorescence materials and paves the way towards constructing stimuli-responsive luminescent supramolecular cages.Beyond the AIE (aggregation-induced emission) phenomenon in small molecules, supramolecules with AIE properties have evolved in the AIE family and accelerated the growth of supramolecular application diversity. 相似文献
77.
78.
Dr. Martin Valldor Dr. Bodo Böhme Dr. Yurii Prots Dr. Horst Borrmann Dr. Peter Adler Dr. Walter Schnelle Dr. Yves Watier Dr. Chang Yang Kuo Dr. Tun‐Wen Pi Dr. Zhiwei Hu Prof. Dr. Claudia Felser Prof. Dr. Liu Hao Tjeng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4626-4631
The novel host–guest compound [Cs6Cl][Fe24Se26] (I4/mmm; a=11.0991(9), c=22.143(2) Å) was obtained by reacting Cs2Se, CsCl, Fe, and Se in closed ampoules. This is the first member of a family of compounds with unique Fe–Se topology, which consists of edge‐sharing, extended fused cubane [Fe8Se6Se8/3] blocks that host a guest complex ion, [Cs6Cl]5+. Thus Fe is tetrahedrally coordinated and divalent with strong exchange couplings, which results in an ordered antiferromagnetic state below TN=221 K. At low temperatures, a distribution of hyperfine fields in the Mössbauer spectra suggests a structural distortion or a complex spin structure. With its strong Fe–Se covalency, the compound is close to electronic itinerancy and is, therefore, prone to exhibit tunable properties. 相似文献
79.
We study two polyhedral lift-and-project operators (originally proposed by Lovász and Schrijver in 1991) applied to the fractional stable set polytopes. First, we provide characterizations of all valid inequalities generated by these operators. Then, we present some seven-node graphs on which the operator enforcing the symmetry of the matrix variable is strictly stronger on the odd-cycle polytope of these graphs than the operator without this symmetry requirement. This disproves a conjecture of Lipták and Tunçel from 2003. 相似文献
80.
Levent Tunçel 《Mathematical Programming》1999,86(1):219-223
Given an m×n integer matrix A of full row rank, we consider the problem of computing the maximum of ∥B
-1
A∥2 where B varies over all bases of A. This quantity appears in various places in the mathematical programming literature. More recently, logarithm of this number
was the determining factor in the complexity bound of Vavasis and Ye’s primal-dual interior-point algorithm. We prove that
the problem of approximating this maximum norm, even within an exponential (in the dimension of A) factor, is NP-hard. Our proof is based on a closely related result of L. Khachiyan [1].
Received November 13, 1998 / Revised version received January 20, 1999? Published online May 12, 1999 相似文献