Li-Ping Zhang

Synthesis, characterisation and ethylene oligomerization behaviour of N -(2-substituted-5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides

A series of N-(2-substituted-5,6,7-trihydroquinolin-8-ylidene)-arylaminonickel(II) dichlorides were synthesized by the one-pot stoichiometric reaction of nickel dichloride, 2-chloro- or 2-phenyl-substituted 5,6,7-trihydroquinolin-8-one, and the corresponding anilines. All nickel complexes were characterized by elemental and spectroscopic analysis. The molecular structures of representative nickel complexes, determined by the single-crystal X-ray diffraction, indicate the different coordination numbers around nickel either four with more bulky ligands or five with less bulky ligands. All nickel complexes, activated with ethylaluminium sesquichloride (Et3Al2Cl3), showed high activities (up to 9.5 × 106 g mol−1 h−1) in ethylene oligomerization for dimer and trimers.

Artificial Light‐Harvesting System Based on Multifunctional Surface‐Cross‐Linked Micelles

In the natural photosynthetic centers of bacteria and plants, antenna chromophores absorb solar light and transfer the excitation energy to the reaction center by highly efficient singlet–singlet energy transfer. Spatial organization of individual chromophores is key to such efficiency: chromophores need to be separated enough to minimize selfquenching without sacrificing the dipole–dipole couplingmediated energy transfer. In addition to its important role in photosynthesis, efficient transfer of energy from multiple chromophores to a single acceptor is of potential significance to solar cells, photocatalysts, optical sensors and light-emitting devices. For these reasons, there has been a great deal of interest in mimicking the natural light-harvesting process. A variety of scaffolds have been used including dendrimers, organogels, porphyrin arrays/assemblies, biopolymer assemblies, and organic–inorganic hybrid materials. Although impressive results have been obtained with the above scaffolds, the multistep synthesis of the complex architectures hampers their scale up and widespread application. Nature relies on a combination of covalent and noncovalent interactions to create the photosynthetic centers. Covalent structures possess excellent stability and noncovalent self-assembled constructs provide order and synthetic efficiency. Herein, we report a biomimetic approach to construct artificial light-harvesting systems. We combined two self-assembling strategies and covalent fixation to prepare a highly efficient antenna system from readily available building blocks. The entire synthesis was achieved by a one-pot reaction, and the product precipitated spontaneously out of the reaction mixture at the end of the reaction. The synthesis of the light-harvesting system is shown in Scheme 1, and is based on the recently reported method to cross-link surfactant micelles. Our model antenna chromophore is 9,10-bis(4-methylphenyl)anthracene (DPA), a compound with high fluorescence quantum yield (90%). Eosin Y disodium salt (EY) is the energy acceptor. Cationic surfactant, 4-(dodecyloxy)benzyltripropargylammonium bromide (1), forms micelles at concentrations of above 0.14 mm in water. Because the surface of the micelle is covered with a dense layer of alkynyl groups, 1,4-diazidobutane-2,3-diol (2) could easily capture the micelle by 1,3dipolar cycloaddition with a Cu catalyst. When 1 and 2 were used in a 1:1 ratio, the resulting surface-cross-linked micelles (SCMs) are water-soluble nanoparticles with numerous alkynes on the surface. Surface functionalization occurred readily upon addition of a THF solution of DPA–N3 (obtained from commercially available DPA by partial bromination and azidation, see the Supporting Information). After 18 hours at room temperature, the DPA-functionalized SCMs (DPA– SCMs) precipitated spontaneously from the 2:1 THF/water mixture, apparently as a result of the increased hydrophobicity of the product. The IR spectrum of the DPA–SCMs showed nearly complete disappearance of the alkyne peaks in the starting SCMs (Figure S1, in the Supporting Information). DLS (dynamic light scattering) indicated an increase in size for the SCMs upon DPA-functionalization (Figure S2, in the Supporting Information). The absorption band of the DPA–SCMs is at 330–420 nm in THF and the emission band at 390–520 nm. These spectra match almost exactly with those of the free, monomeric DPA in solution (Figure S3, in the Supporting Information). Therefore, the DPA concentration ([DPA]SCMs) in this system can be determined from the absorption spectrum and the molar coefficient extinction of DPA. A frequent issue in light-harvesting systems with multiple donors is the self-quenching and/or excimer formation caused by the proximity of the chromophores. These pathways interfere with the energy transfer and lower the overall efficiency, and often require elaborate strategies to overcome. Excitingly, the fluorescence quantum yield was 0.80 and 0.90 for the micelle-bound DPA and the free chromophore, respectively (see the Supporting Information). Clearly, neither self-quenching nor excimer formation was significant in the highly crowded system. We suspect there are [*] H.-Q. Peng, Dr. Y.-Z. Chen, Prof. Q.-Z. Yang, Prof. L.-Z. Wu, Prof. C.-H. Tung, Prof. L.-P. Zhang Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry Chinese Academy of Sciences 29 Zhongguancun East Road, Beijing 100190 (China) E-mail: qzyang@mail.ipc.ac.cn H.-Q. Peng, Prof. Q.-X. Tong Department of Chemistry, Shantou University Shantou, Guangdong 515063 (China) E-mail: qxtong@stu.edu.cn

Reversible Sol-to-Gel Transformation of Uracil Gelators: Specific Colorimetric and Fluorimetric Sensor for Fluoride Ions

A new type of anthracene organogelator based on uracil was obtained using organic aromatic solvents, cyclohexane, DMSO, ethanol, and ethyl acetate. It was further characterized by field-emission scanning electron microscopy and transmission electron microscopy. Specifically, the resulting organogels were demonstrated to be promising colorimetric and fluorescent sensors toward fluoride ions with high sensitivity and selectivity, accompanying the disruption of the gelators. Spectroscopic study and (1)H NMR titration experiment revealed that the deprotonation of the hydrogen atom on the N position of uracil moiety by fluoride ions is responsible for the recognition events, evidenced by immediate transformation from the sol phase to the gel state upon adding a small amount of a proton solvent, methanol. The process is reversible, with zero loss in sensing activity and sol-to-gel transformation ability even after five runs.

Microreactor-controlled selectivity in organic photochemical reactions*

Molecular-sieve zeolites, Nafion membranes, low-density polyethylene films, and mixed surfactant vesicles have been used as microreactors to carry out organic photochemical reactions. The photo-cycloadditions of diaryl compounds with long flexible chains included in NaY zeolite or low-density polyethylene films yield intramolecular photocyclomers to the exclusion of intermolecular products. The photosensitized oxidation of alkenes included in pentasil zeolites or Nafion membranes or vesicles can be directed selectively toward either the singlet oxygen-mediated or the superoxide radical anion-mediated products by controlling the status and location of the substrate and sensitizer molecules in the reaction media. The photo-Fries rearrangement of phenyl phenylacetates included within NaY and pentasil zeolites or Nafion membranes gives either ortho-hydroxyphenones or decarbonylation products depending on the size/shape of the microreactors and the substrate molecules. All these results demonstrate the utility of microreactors to control the product selectivity in organic photochemical reactions.

Water-in-oil microemulsions as microreactors to control the regioselectivity in the photocycloaddition of 9-substituted anthracenes

Abstract The photocycloaddition of five 9-substituted anthracenes [AnCH2N+(CH3)3Br− ( 1 ), AnCH2COONa ( 2 ), AnCH2OH ( 3 ), AnCOCH3 ( 4 ), AnCH3 ( 5 ), An=9-anthryl] incorporated in water-in-oil microemulsions prepared from sodium bis(2-ethylhexyl) sulfosuccinate (AOT), methylene chloride and water has been investigated. While irradiation of the above substrates in methylene chloride, and 5 in the microemulsions also, mainly gave rise to their head-to-tail (h-t) photocyclomers, photoirradiation of the samples of 1–4 incorporated in the microemulsions almost exclusively yielded the head-to-head (h-h) photocyclomers. These observations were interpreted in terms of the preorientation of the substrate molecules at the interface of the water pool in the microemulsions.

Two-photon-pumped frequency-upconverted yellow lasing in a novel dye solution

Two-photon induced frequency upconversion emission and two-photon-pumped (TPP) lasing properties of a novel dye, trans-2-[p-(N-ethyl-N-(hydroxyethyl)amino)styryl]-N-methylthiazolinium iodide (1) were investigated. This dye exhibits excellent TPP lasing at ∼577 nm when it is pumped with a 1064 nm pulsed laser beam. The net conversion efficiency from the absorbed 1064 nm pump energy to the ∼577 nm upconverted lasing energy was measured to be ∼2.2%.

Switch between charge transfer and local excited states in 4-aminophenyl-substituted Hantzsch 1,4-dihydropyridine induced by pH change and transition metal ions

The absorption and fluorescence spectra of a Hantzsch 1,4-dihydropyridine derivative bearing a N,N-dimethylaminophenyl group at 4-position (H(2)Py-PhN(CH(3))(2)) in aprotic solvents have been examined and compared to model compounds 4-phenyl- and 4-methyl-substituted Hantzsch 1,4-dihydropyridines (H(2)Py-Ph and H(2)Py-Me). While H(2)Py-Ph and H(2)Py-Me show fluorescence around 420 nm from the local excited state of the dihydropyridine chromophore, H(2)Py-PhN(CH(3))(2) exhibits fluorescence around 520 nm from the intramolecular charge transfer (ICT) state involving the aniline and dihydropyridine groups as donor and acceptor, respectively. Upon addition of an acid to the solution of H(2)Py-PhN(CH(3))(2), the amino group in the aniline is protonated. Thus, the photoinduced intramolecular charge transfer is prevented, and only the fluorescence from the local excited state of the dihydropyridine chromophore can be detected. These changes in the fluorescence behavior are fully reversible: subsequent addition of a base to the acidic solution leads to the recovery of the ICT fluorescence and the quenching of the local fluorescence. Transition metal ions also can switch the fluorescence of H(2)Py-PhN(CH(3))(2). Evidence for the interaction between transition metal ions and the amino group in the dimethylaniline have been provided by absorption and emission spectrum as well as NMR studies.

Two-photon-pumped frequency-upconverted lasing and optical power limiting properties of vinylbenzothiazole-containing compounds in solution

Two-photon induced frequency-upconversion emission, two-photon-pumped (TPP) lasing and optical limiting properties of trans-2-[p-(N-methyl-N-hydroxyethylamino)styryl]-N-methylbenzothiazolinium iodide (1) and trans-2-[p-(N-ethyl-N-hydroxyethylamino)styryl]-N-methylbenzothiazolinium iodide (2) were investigated. These two compounds exhibit excellent TPP lasing at 634 nm when pumped with a 1064 nm pulsed laser beam, and highly efficient optical limiting performance in 1 cm path-length dimethyl formamide solution pumped with 1064 nm laser pulses at 0.01 ∼ 6.75 mJ. Significantly, these compounds are very stable upon exposure to light for a long time.

Pyrazolofluostatins A–C, Pyrazole-Fused Benzo[a]fluorenes from South China Sea-Derived Micromonospora rosaria SCSIO N160

Pyrazolofluostatins A-C (1-3), three new benzo[a]fluorenes with an unprecedented carbon skeleton, were obtained from the South China Sea-derived Micromonospora rosaria SCSIO N160. Their structures were elucidated by extensive spectroscopic analyses. The structure of pyrazolofluostatin A (1) was confirmed by X-ray crystallographic analysis. Notably, 1-3 possessed a benzo[cd]indeno[2,1-f]indazol skeleton with a pyrazole-fused 6/5/6/6/5 pentacyclic ring system. Pyrazolofluostatin A (1) showed moderate antioxidation activity (EC50 48.6 μM).

Water-soluble copolymeric materials: switchable NIR two-photon fluorescence imaging agents for living cancer cells

A simple one-pot multi-component ROMP of hydrophilic, spiropyran (SP) and tert-butyloxycarbonyl-protected (Boc-protected) amino-functionalized norbornenes was developed, and a series of water-soluble copolymeric materials were provided. The photochromic SP moiety endows the copolymers the properties of switchable fluorescence imaging with alternating near-IR (NIR) two-photon and visible single-photon excitations; thereby the copolymers can serve as a promising NIR two-photon fluorescent probe for living cancer cells. The cationic ammonium group enhances the cell transporting capability of the copolymers as well. The present strategy of one-pot ROMP also makes polynorbornene a modular and flexible scaffold in designing and synthesizing specifically biocompatible polymers with applications in imaging, diagnosis and therapy.