Chemla effect

The self-exchange velocity (SEV), which can be calculated from molecular dynamics simulation, has reproduced the Chemla effect. Fur-... 

Binary alkali nitrates have been systematically studied the isotherms are shown in Fig. 6. The Chemla effect occurs in all systems except for (Li, Na)N03. Figure 6 shows that with an increase in temperature the crossing point shifts toward higher concentrations of the smaller cation. 

Figure 8. Isotherms of l and Mc in (Li, Cs)Cl at 973 K. (Reprinted from I. Okada and H. Horinouchi, The Chemla Effect in the Mobilities in the Molten Binary System of Lithium Chloride and Caesum Chloride, J. Electroanal. Chem 396 547, Fig. 4, Copyright 1995 with permission of Elsevier Science.)...

Chemla s group proposed an associated model more than 30 years ago for the purpose of interpreting the Chemla effect soon after its discovery. For example, the following chemical equilibria were considered ... 

According to the model proposed by Klemm and Schafer, - the Chemla effect is explained qualitatively. Although molten LiBr has a... 

Okada et al. have presented a dynamic dissociation model, which is schematically shown in one dimension in Fig. 4. They assumed that the separating motion of a cation (or anion) of interest from the reference anion (cation), which is called the self-exchange velocity,is the electrically conducting process, which will be considered in Section III.7( ) in more detail. The Chemla effect can also be reproduced by the SEV. 

Internal mobilities were calculated for molten LiCl and (Li, Cs)Cl (Xcs = 0.90). The values are given in Table 8, which shows that the calculated mli is much smaller than Ucs, that is, the Chemla effect can be reproduced by MD simulation. 

Thus the SEV can reproduce apparently anomalous phenomena in electrical conductance such as the Chemla effect, a maximum of electrolytic conductivity of some salts containing LL as a function of pressure, an expected maximum in electrolytic conductivity as a func-... 

A similar idea on the incomplete dissociation of molten salts was presented by Klemm and Schafer (1996). Their model was stimulated by a qualitative explanation of the Chemla effect made by Klemm (1984), which is the crossing over of the mobility isotherms at a certain temperature. This means that at high concentrations of a larger sized cation, its mobility is greater than that of the smaller one. This effect was first observed in the LiBr-KBr system by Mehta et al. (1969), was also observed later in many other monovalent systems, and named after one of its discoverers. 

Based on the fundamental dipole moment concepts of mesomeric moment and interaction moment, models to explain the enhanced optical nonlinearities of polarized conjugated molecules have been devised. The equivalent internal field (EIF) model of Oudar and Chemla relates the j8 of a molecule to an equivalent electric field ER due to substituent R which biases the hyperpolarizabilities (28). In the case of donor-acceptor systems anomalously large nonlinearities result as a consequence of contributions from intramolecular charge-transfer interaction (related to /xjnt) and expressions to quantify this contribution have been obtained (29). Related treatments dealing with this problem have appeared one due to Levine and Bethea bearing directly on the EIF model (30), another due to Levine using spectroscopically derived substituent perturbations rather than dipole moment based data (31.) and yet another more empirical treatment by Dulcic and Sauteret involving reinforcement of substituent effects (32). 

Chemla and Ferreira effected lithiozincation of TMS propargyl chloride to prepare chloroal-lenylzinc bromide reagents (Table 21)33. Subsequent reaction of these reagents with N-t-butyl-substituted sulfoximines yielded the related traws-sulfoxinyl aziridines, arising from internal displacement of the chloride substituent of the anti sulfinamide adduct. A transition state in which the f-BuSO group is eclipsed with the alkynyl (vs R) substituent accounts for the preferred formation of the major A-sulfinyl diastereomer (equation 41). 

At the end of the 1960 s, the Kurtz and Perry powder SHG method was introduced.(8) For the first time, rapid, qualitative screening for second order NLO effects was possible. The stage was set for a rapid introduction of new materials, both inorganic and organic. The early history summarized here is based on a more extensive report presented by Zyss and Chemla (8) in their series "Nonlinear Optical Properties of Organic Molecules and Crystals."... 

D. J. William (ed.), Nonlinear Optical Properties of Organic and Polymeric Materials, ACS Symp. Ser. 233, American Chemical Society, Washington, DC, 1983 D. S. Chemla and J. Zyss (eds), Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, New York, 1987 S. R. Marder, J. E. Sohn and G. D. Stucky (eds), Materials for Nonlinear Optics Chemical Perspectives, ACS Symp. Ser. 455, American Chemical Society, Washington, DC, 1991 P. N. Prasad and D. J. Williams, Introduction to Nonlinear Optical Effects in Molecules and Polymers, Wiley-Interscience, New York, 1991. 

L. Torcheux, A. Mayeux, and M. Chemla, Electrochemical coupling effects on the corrosion of silicon samples in HE solutions, J. Electrochem. Soc. 142, 2037, 1995. 

The oriented gas model was first employed by Chemla et al. [4] to extract molecular second-order nonlinear optical (NLO) properties from crystal data and was based on earlier work by Bloembergen [5]. In this model, molecular hyperpolarizabilities are assumed to be additive and the macroscopic crystal susceptibilities are obtained by performing a tensor sum of the microscopic hyperpolarizabilities of the molecules that constitute the unit cell. The effects of the surroundings are approximated by using simple local field factors. The second-order nonlinear response, for example, is given by... 

Table II provides a survey of representative calculations of p and 7 of molecular aggregates with an eye toward determining the bulk susceptibilities or, at least, toward addressing the effect that crystal packing has on the NLO responses. Initial studies focused on the first hyperpolarizability, and this was a consequence of the earlier work by Chemla, Zyss, and collaborators and of the necessity to improve the oriented gas model (see Section II). Dirk et al. [47] studied dimers of urea and of (A)-(5-nitropyrid i)-2(i.)-prolinol (PNP) by adopting a Pariser Parr Pople (PPP) Hamiltonian. They showed the limits of...

See e.g. Nonlinear Optical and Electroactive Polymers , Prasad, P. N., Ulrich, D. R., Eds. Plenum Press New York, 1988. Nonlinear Optical Effects in Organic Polymers , Messier, J., Kajzar, F., Prasad, P., Ulrich, D., Eds. Kluwer Academic Publishers Dordrecht, The Netherlands, 1989. Non Linear Optical Properties of Organic Molecules and Crystals , Chemla, D. S., Zyss, J., Eds. Academic Press Orlando, FL, 1987, Vol. 2,... 

Magdelenat, H. Turq, P. Tivant, P. Chemla, M. Menez, R. Drifford, M, Biopolymers. 1979, l8. 187-201. The effect of counterion substitution on the transport properties of polyelectrolyte solutions. 

Gabizon A, Chemla M, Tzemach D, et at Liposome longevity and stability in circulation effects on the in vivo dehvery to tumors and therapeutic efficacy of encapsulated anthracyclines. J Drag Target 3 391-398, 1996... 

Nitroaniline is the standard of comparison for nonlinear optical compounds. The molecule is noncentrosymmetric on the molecular level and has a high hyperpolarizability (P = 34.5 x 10" esu, Oudar and Chemla, 1977), but it crystallizes centrosymmetrically therefore, it does not show second-order nonlinear optical effects in the crystalline phase (Miyata et al., 1994). In contrast, 3-nitroaniline crystallizes in a noncentrosymmetric space group, but the P value is much lower (P = 6.0 X esu, Oudar and Chanla, 1977) than the value of 4-nitroaniline, because the charge transfer in the latter case (para-isomer) is much stronger. 

See, for example, Chemla and Zyss also Prasad, P. N., and D. J. Williams. 1990. Introduction to Nonlinear Optical Effects in Molecules and Polymers. New York Wiley (Interscience). 

Several methods have been developed in order to determine the macroscopic optical properties [63], of which the simplest is the oriented gas model due to Chemla et al. [64, 65] In that method, the hnear and nonlinear susceptibilities (Eq. (8.2) are calculated from simple tensor sums of the (hyper)polarizabihties of the molecules constituting the elementary unit cell. Corrective factors can subsequently be added to account for the effects of local electric fields. The relevance of this method is ensured provided the intermolecular interactions are weak, while the macroscopic responses are strongly dependent on the values of local field factors. More sophisticated schemes take into account the intermolecular interactions. They include the supermolecule model [66-69], where an aggregate of... 

To increase the bulk NLO effects, one first needs to optimize the molecular hyperpolarizability. Several simple models have been developed to interpret second-order responses. The equivalent field model (EIF), developed in 1975 by Oudar and Chemla [33], was one of the first attempts. It was proposed that a major portion of the second-order response in Tt-organic chromophores could be predicted from the ground-state deformation of the TT-electron distribution by appended substituents. The relation between the TT-distortion and the quadratic hyperpolarizability is given by ... 

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