Formation of the charge-transfer exciton in 1,3,5-triphenyl-2-pyrazoline nanocrystals

2003 ◽  
Vol 81 (1) ◽  
pp. 7-13 ◽  
Author(s):  
Hongbing Fu ◽  
Debao Xiao ◽  
Ruimin Xie ◽  
Xuehai Ji ◽  
Jian-Nian Yao
Keyword(s):  
Charge Transfer ◽  
Fluorescence Spectra ◽  
Molecular Model ◽  
Thermal Fluctuation ◽  
Nanocrystal Size ◽  
Absorption Feature ◽  
Model Calculations ◽  
Size Dependent ◽  
Dependent Property ◽  
Reprecipitation Method

A series of 1,3,5-triphenyl-2-pyrazoline (TPP) nanocrystals were prepared by the reprecipitation method. The electronic transitions of TPP nanocrystals have been studied using both absorption and fluorescence spectra. An absorption feature at about 400 nm gradually appeared with increasing nanocrystal size. This feature resulted from the formation of the charge-transfer (CT) exciton in nanocrystals. It was also supported by the longer decay time of the nanocrystal emission from CT compared with that of the solution emission from S1 at 298 K. On the other hand, the different behavior of the molecular π–π* and n–π* transitions originates from the different overlapping modes of the pyrazoline π orbital and n-electron orbital, according to the molecular model calculations. The nanocrystal emission from both the S1 and CT states was found at 77 K; moreover, the emission intensity redistributed from S1 to CT with increasing nanocrystal size. In contrast, at 298 K, only the emission from the CT states was observed, since the thermal fluctuation easily relaxes the excited electrons into CT states through vibration. Key words: reprecipitation method, organic nanocrystals, charge-transfer exciton, size-dependent property.

Synthesis, Characterization and Photophysical Properties of Rhenium(I) Complexes Containing 4,5-Diazafluorene Ligan

2011 ◽  
Vol 239-242 ◽  
pp. 2612-2615
Author(s):  
Jie Xiu Wang ◽  
Feng Zhao
Keyword(s):  
Charge Transfer ◽  
Fluorescence Spectra ◽  
Photophysical Properties ◽  
Absorption And Fluorescence Spectra ◽  
Rhenium Complexes ◽  
H Nmr ◽  
Ligand Charge Transfer

Two related tricarbonyl rhenium complexes with the formula of [Re(CO)3(L)Cl], where L=4,5-diazafluoren-9-one (Dafo-Re) and 9-(phenylamino)-4,5-diazafluoren (PADF-Re) were successfully synthesized with the aim to explore the effect of the geometry of Dafo on Rhenium(I) coordination, and characterized by1H NMR. Photophysical behaviors are investigated by UV–vis absorption and Fluorescence spectra. The two complexes Dafo-Re and PADF-Re show metal-to-ligand charge transfer absorptions at ca.391nm, ca.394 nm and emissions at ca.492nm, ca.470nm, respectively.

A CORRESPONDING RELATION BETWEEN ELECTROLUMINESCENT INTENSITY AND THE ENERGY AND CHARGE TRANSFER IN DOPED ORGANIC ELECTROLUMINESCENT DEVICES

2008 ◽  
Vol 22 (30) ◽  
pp. 2979-2986
Author(s):  
HONG-JIAN LI ◽  
ZHI-JUN WANG ◽  
JUN-XI WANG ◽  
XUE-YONG LI ◽  
HUI XIA ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Conjugated Polymer ◽  
Fluorescence Spectra ◽  
Dopant Concentration ◽  
Quantitative Relation ◽  
Efficient Energy Transfer ◽  
Electroluminescent Devices ◽  
Efficient Energy ◽  
Hamiltonian Model ◽  
Organic Electroluminescent

In doped organic electroluminescent devices (OLEDs), the changes of the fluorescence spectra occurred due to the energy and charge transfer from guest to host. A quantitative relation between the energy and charge transfer for doping OLEDs was studied by means of a Hamiltonian model. It was found that there is a corresponding relation between the EL intensity of doped PVK and the amount of the transferred charge and the change of the energy derived from charge transfer with dopant concentration, and the more the amount of the transferred charge and the decreasing of the energy from charge transfer, the higher the EL intensity in doped OLEDs. We can deduce that the efficient energy transfer results from the transferred charge between PVK and perylene. Based on the transport mechanism of carriers in conjugated polymer, an expression of conductivity was presented. Calculated results indicated that there is also a corresponding relation between the EL intensity of doped PVK and conductivities with dopant concentration. The larger the conductivities, the higher the EL intensity in doped OLEDs.

The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

2001 ◽  
Vol 79 (2) ◽  
pp. 238-255 ◽  
Author(s):  
Ulrike Spohr ◽  
Nghia Le ◽  
Chang-Chun Ling ◽  
Raymond U Lemieux
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Model ◽  
Aromatic Amino Acids ◽  
Hydroxyl Group ◽  
Bulk Solution ◽  
Anomeric Effect ◽  
Nmr Studies ◽  
Intermolecular Hydrogen Bonds ◽  
Model Calculations ◽  
Derivatives Of

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.

Size-Dependent Property and Cell Labeling of Semiconducting Polymer Dots

2014 ◽  
Vol 6 (13) ◽  
pp. 10802-10812 ◽  
Author(s):  
Kai Sun ◽  
Haobin Chen ◽  
Lei Wang ◽  
Shengyan Yin ◽  
Haiyu Wang ◽  
...  
Keyword(s):  
Cell Labeling ◽  
Semiconducting Polymer ◽  
Size Dependent ◽  
Polymer Dots ◽  
Dependent Property ◽  
Semiconducting Polymer Dots

scholarly journals Effect of Axial Porosities on Flexomagnetic Response of In-Plane Compressed Piezomagnetic Nanobeams

Symmetry ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 1935 ◽  
Author(s):  
Mohammad Malikan ◽  
Victor A. Eremeyev ◽  
Krzysztof Kamil Żur
Keyword(s):  
Material Properties ◽  
Gradient Elasticity ◽  
Small Scale ◽  
Stability Equation ◽  
Strain Gradients ◽  
Size Dependent ◽  
Different Types ◽  
Dependent Property ◽  
The Stability ◽  
Transverse Deflection

We investigated the stability of an axially loaded Euler–Bernoulli porous nanobeam considering the flexomagnetic material properties. The flexomagneticity relates to the magnetization with strain gradients. Here we assume both piezomagnetic and flexomagnetic phenomena are coupled simultaneously with elastic relations in an inverse magnetization. Similar to flexoelectricity, the flexomagneticity is a size-dependent property. Therefore, its effect is more pronounced at small scales. We merge the stability equation with a nonlocal model of the strain gradient elasticity. The Navier sinusoidal transverse deflection is employed to attain the critical buckling load. Furthermore, different types of axial symmetric and asymmetric porosity distributions are studied. It was revealed that regardless of the high magnetic field, one can realize the flexomagnetic effect at a small scale. We demonstrate as well that for the larger thicknesses a difference between responses of piezomagnetic and piezo-flexomagnetic nanobeams would not be significant.

A naked-eye, selective and sensitive chemosensor for fluoride ion

2010 ◽  
Vol 64 (6) ◽  
Author(s):  
Puhui Xie ◽  
Fengqi Guo ◽  
Weifeng Wang ◽  
Xiyang Liu
Keyword(s):  
Charge Transfer ◽  
Fluorescence Quenching ◽  
Fluorescence Spectra ◽  
Color Change ◽  
Fluoride Ion ◽  
Absorption And Fluorescence Spectra ◽  
Strong Fluorescence ◽  
Naked Eye ◽  
Acridine Yellow ◽  
Intermolecular Charge Transfer

AbstractEffect of the addition of six different anions on the absorption and fluorescence spectra of acridine yellow G (AYG) was examined. Only the F− anion could induce a visible color change observable with naked eye and a strong fluorescence quenching with K SV of 8.3 × 104 mol−1 L in CH3CN solutions. Calculated results of the interaction between the F− anion and acridine yellow G using the B3LYP/6-31G(d) program showed that the intermolecular charge transfer through the formation of an H-bond between AYG and F− is an essential sensor mechanism.

scholarly journals DFT Modelling of Tripeptides (Lysine-Tryptophan-Lysine) Interacting with Single Walled Carbon Nanotubes

2010 ◽  
Vol 7 (3) ◽  
pp. 870-874 ◽  
Author(s):  
Navaratnarajah Kuganathan
Keyword(s):  
Density Functional Theory ◽  
Charge Transfer ◽  
Density Functional ◽  
Single Walled Carbon Nanotubes ◽  
Binding Energies ◽  
Functional Theory ◽  
Model Calculations ◽  
Walled Carbon Nanotubes ◽  
Dft Modelling ◽  
Covalent Nature

Model calculations are performed to predict the nature of interaction between SWNT and a tripeptide (Lys-Trp-Lys) and to calculate the binding energies and charge transfer between these two species using density functional theory. DFT calculations indicate that the interaction is of a non covalent nature. Minimal charge transfer is observed between SWNT and Lys-Trp-Lys.

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