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991.
Chattopadhyaya M Alam MM Chakrabarti S 《Physical chemistry chemical physics : PCCP》2012,14(26):9439-9443
Herein, we predict that graphene nanoribbons will be nonplanar under the influence of a critical perpendicular field. Our investigation demonstrates that the perpendicular field induces mixing of σ and π orbitals in graphene nanoribbons through the second order Stark effect which eventually modulates the electron-nuclear interaction strongly in favor of a bent structure. 相似文献
992.
Alam MM Chattopadhyaya M Chakrabarti S 《Physical chemistry chemical physics : PCCP》2012,14(3):1156-1165
For the first time, we report the effect of interference between different optical channels on the two-photon absorption (TPA) process in three dimensions. We have employed response theory as well as a sum-over-states (SOS) approach involving few intermediate states to calculate the TPA parameters like transition probabilities (δ(TP)) and TPA tensor elements. In order to use the limited SOS approach, we have derived a new formula for a generalized few-state-model (GFSM) in three dimensions. Due to the presence of additional terms related to the angle between different transition moment vectors, the channel interference associated with the TPA process in 3D is significantly different and much more complicated than that in 1D and 2D cases. The entire study has been carried out on the two simplest Reichardt's dyes, namely 2- and 4-(pyridinium-1-yl)-phenolate (ortho- and para-betain) in gas phase, THF, CH(3)CN and water solvents. We have meticulously inspected the effect of the additional angle related terms on the overall TPA transition probabilities of the two 3D isomeric molecules studied and found that the interfering terms involved in the δ(TP) expression contribute both constructively and destructively as well to the overall δ(TP) value. Moreover, the interfering term has a more conspicuous role in determining the net δ(TP) associated with charge transfer transition in comparison to that of π-π* transition of the studied systems. Interestingly, our model calculations suggest that, for o- and p-betain, the quenching of destructive interference associated with a particular two-photon process can be done with high polarity solvents while the enhancement of constructive interference will be achieved in solvents having relatively small polarity. All the one- and two-photon parameters are evaluated using a range separated CAMB3LYP functional. 相似文献
993.
Meral G. Babaoğlu Serap Safran Özlem Çiçek Hasan Ağıl Ercan Ertekin Md.Shahriar A. Hossain Ekrem Yanmaz Ali Gencer 《Journal of magnetism and magnetic materials》2012
The effect of aromatic hydrocarbon (benzene, C6H6) addition on lattice parameters, microstructure, critical temperature (Tc), critical current density (Jc) of bulk MgB2 has been studied. In this work only 2 mol% C6H6 addition was found to be very effective in increasing the Jc values, while resulting in slight reduction of the Tc. Jc values of 2 mol% C6H6 added MgB2 bulks reached to 1.83×106 A/cm2 at 15 K and 0 T. Microstructural analyses suggest that Jc enhancement is associated with the substitution of carbon with boron and which also results in the smaller MgB2 grain size. The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the Tc by carbon addition. We note that our results show the advantages of C6H6 addition include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in Jc of MgB2, compared to un-doped samples. 相似文献
994.
Biological motors, driven by the conversion of chemical energy into mechanical energy, are much more efficient than man-made machines. The development of such efficient biomimetic motor systems in vitro is currently a vital need. However, great difficulty lies in how to integrate the sophisticated functions of the constituent components to obtain a performance as in the case of natural living systems. Based on 'active' and 'passive' self-organization principles, it has been demonstrated that the functions of motor protein systems can be integrated to obtain complex hierarchical structures that can work as actuators. Most of the works discussed here concern two-dimensional behavior, and recent works aim to explore the three-dimensional features of such artificial bio-mechanical systems. 相似文献
995.
Oxidation of primary aliphatic aldehydes with p-trifluoromethylphenyl(difluoro)-λ(3)-bromane in dichloromethane at 0 °C afforded acid fluorides selectively in good yields, while that of aromatic aldehydes in chloroform at room temperature produced aryl difluoromethyl ethers. A larger migratory aptitude of aryl groups compared to primary alkyl groups during a 1,2-shift from carbon to an electron-deficient oxygen atom in bromane(III) Criegee-type intermediates will result in these differences in the reaction courses. 相似文献
996.
Mariano Pracella Cristiano Pancrazi Md. Minhaz-Ul Haque Aldo D’Alessio 《Journal of Thermal Analysis and Calorimetry》2011,103(1):95-101
Composites of polystyrene (PS) with cellulose microfibres and oat particles, obtained by melt mixing, were examined. The compatibilization
of the composites was carried out by addition of maleic anhydride-functionalized copolymers (SEBS-g-MA, PS-co-MA) and poly(ethylene glycol) to improve the fibre–matrix interfacial interactions. The plain components and their composites
were characterised by FT-IR, DSC, TGA, SEM microscopy and mechanical tests. The properties of the various systems were analysed
as a function of both fibre and compatibilizer amount. The compatibilized PS composites showed enhanced fibre dispersion and
interfacial adhesion as a consequence of chemical interactions between the anhydride groups on the polymer chains and the
hydroxyl groups on the fibres, as demonstrated by FT-IR spectroscopy. DSC analysis pointed out a neat increase of T
g of composites on addition of SEBS-g-MA, as compared to PS-co-MA. The thermal stability of composites was also influenced
by the type and amount of fibres, as well as by the structure and concentration of compatibilizer. The effect of the reactive
copolymers on the composites properties was accounted for on the basis of the polymer–polymer miscibility and chemical interactions
at the matrix/filler interface. 相似文献
997.
Alam MM Chattopadhyaya M Chakrabarti S 《Physical chemistry chemical physics : PCCP》2011,13(20):9285-9292
In the present work, we have studied the two-photon absorption (TPA) properties of some selective molecules containing triarylborane and 1-naphthylphenylamine as the acceptor and donor moiety, respectively. The calculations are performed by using the state-of-the-art linear and quadratic response theory in the framework of the time dependent density functional theoretical method. The TPA parameters are calculated with CAMB3LYP functional and the cc-pVDZ basis set. The one-photon results indicate that both the electronic transitions (S(0)-S(1) and S(0)-S(2)) are associated with the charge transfer interaction between the donor and acceptor moieties along with the reorganization of the π-electron density. All these chromophores are found to have very strong two-photon active modes. In order to find out the origin of large TP transition probability of these molecules, we have performed two-state model (TSM) and sum-over-states (SOS) calculations. We have found that the TSM failed to reproduce the correct trend of the TP transition probability of the molecules obtained from the response theory, while SOS is quite successful in doing so. The whole study indicates that the transition moments between the excited states play a pivotal role in controlling the TP transition probabilities of these molecules. The role of solvent in the TP transition probability of these molecules has meticulously been scrutinized within the polarized continuum model (PCM). Further more, we have benchmarked our theoretical findings by calculating the TPA cross-section of a boron and nitrogen containing a charge transfer molecule for which the experimental result is available and we found that our theoretical result is in good agreement with the experimental one which definitely demonstrates the potential of all these light-emitting diode molecules as TP active materials too. 相似文献
998.
Miran MS Kinoshita H Yasuda T Susan MA Watanabe M 《Chemical communications (Cambridge, England)》2011,47(47):12676-12678
The temperature dependence of the N-H proton chemical shift in protic ionic liquids (PILs) and FT-IR spectra of the N-H bonds indicated the presence of strong hydrogen bonds between the protonated cation and the anion, depending on the ΔpK(a) of the constituent acid and base, and their successive breaking with temperature, which may explain the characteristic properties of PILs such as relatively low ionicity and its decrease with temperature. 相似文献
999.
Islam MM Valiyev F Lu HF Kuo MY Chao I Tao YT 《Chemical communications (Cambridge, England)》2011,47(7):2008-2010
A novel p-channel semiconductor pyreno[4,5-a]coronene has been synthesized and characterized. The highly fused π-conjugated framework has a twisted geometry with an excellent on-top cofacial π-π stacking in the crystal structure and with a centroid-to-centroid distance of 3.808 ?. Single-crystal field effect transistors based on the molecule exhibit a high mobility of ~0.89 cm(2) V(-1) s(-1) and an on/off ratio of ~6 × 10(4). 相似文献
1000.
Zhirong L Azhar Uddin M Zhanxue S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):1013-1016
Na-bentonite has been studied extensively because of its strong adsorption capacity and complexation ability. In this work, surface area, total pore volume, mean pore diameter, TG, DTA, FT-IR and XRD were carried out in order to reveal the characteristics of natural Na-bentonite. XRD and FT-IR of natural Na-bentonite (China) and Cu-loaded Na-bentonite as a function of Na-bentonite dosage and temperature using batch technique were characterized in detail, respectively. 相似文献