Push-pull applications

Thus, the sensitivity of a thermistor is a quadratic function of operating temperature. The optimum sensitivity is typically 4% °C 1. Because of their nonlinear response, thermistors are sometimes linearized by placing a resistor of similar nominal value in parallel with the thermistor, with a resulting loss of sensitivity. This is not generally necessary for thermochemical sensors, particularly for the push-pull applications, because the temperature range involved is small. For direct temperature measurement, the detection limit of 10 4oC can be achieved with a conventional Wheatstone bridge. 

Swain and Eddy have queried the wide applicability of the S l and Sif2 mechanisms and favored a push-pull termolecular process for the reaction of pyridine with methyl bromide in benzene solution for example, they have suggested that the effects observed on the addition of methanol, phenol, p-nitrophenol, and mercuric bromide to the reaction mixture can be explained by an intermediate of type 168. ... 

Interesting push-pull dienes, 1-dialkylamino-4-nitro-l,3-butadienes, are prepared by the application of this addition-elimination reaction. (Eq. 4.22).28... 

Push-push/pull-pull chromophores 118 and 119 have exhibited material properties to show their prospect for several applications particularly in the fields of two-photon microscopy and optical power limitation <1999CC2055, 2002SM17>. 

For the application of this push-pull stabilization principle to intermolecular C-H insertion, see Davies. H.M.L. Hansen, T. 

In more recent work, Chiu and co-workers [167, 168] have reported an intramolecular 1,3-dipolar cycloaddition approach toward the pseudolaric acids 85, in which the di-polarophile is an unactivated 1,1-disubstituted alkene. Hence, treatment of the diazo ketone 86 with catalytic Rh2(OAc)4 furnished a mixture of tricyclic products 87 and 88 in nearly equal proportions (Scheme 19.13). The synthesis of 2-pyridones [169] and their application to the ipalbidine core [170] has been described. The pentacyclic skeleton of the aspidosperma alkaloids was prepared via the cycloaddition of a push-pull carbonyl ylide [171]. The dehydrovindorosine alkaloids 89 have also been investigated, in which the a-diazo-/ -ketoester 90 undergoes a facile cycloaddition to furnish 91 in... 

Apart from the class of push-pull molecules many other polyconjugated systems exhibit peculiar electronic properties which make them very attractive for technological applications. Most of these systems do not posses a permanent dipole moment and their mutual interactions are due only to London dispersion forces. Also in this case, however,... 

Shi Y, Lin W, Olson DJ, Bechtel JH, Wang W (1999) Microstrip line-slot ground electrode for high-speed optical push-pull polymer modulators. In Organic thin films for photonic applications. Optical Society of America, Washington DC, p 20... 

The flat dies, or slot dies as they are sometimes called, are used to produce webs in a variety of processes. They all have an interior manifold for distributing the plastic and lips for adjusting the final profile of the web (extrudate). Some dies have movable restrictor bars for changing the manifold for proper melt distribution (Figure 17.10). All flat dies have flexible lips that can be adjusted by bolts to remove humps or bumps in the web s profile. Die lips can have their adjustment bolts push only, where internal plastic melt pressures are adequate to keep the lips positioned against the bolts, or can be push/pull for low pressure applications. Direct acting or differential thread designs (for minute adjustments) are available. Profile variations of at least 3% or less can be achieved with flat dies. 

The numerator in equation (22-26) represents the processes occurring in the mobile phase, while the denominator represents the processes occurring in the stationary phase. Such a situation can be realized by combining a chiral stationary phase in a push-pull mode with a chiral mobile phase of opposite con-hguration, where two enantiomers of the chiral selector are involved, one for the chiral stationary phase and the other for the chiral mobile phase. The most selective chiral chromatographic system should be encountered when one enantiomer binds to the immobilized chiral selector in the stationary phase, whereas the other enantiomer predominantly associates with the chiral mobile-phase additive [158]. The above treatment is applicable to all applications regarding the use of chiral mobile phases. 

The chemical information available through LFER is primarily the reaction constant p, but this value depends upon the substituent constants selected for the construction of the LFER. The u values available are ct, ct", ct" or and Ui, these quantities are listed, for many substituents, in Tables 7-1, 7-3, 7-4, 7-6, and 7-7. A reasonable approach is to plot log k against the substituent constant defined by a standard reaction that is expected to be most like the reaction under study. It is also reasonable to plot log k against several of the ct quantities, seeking the best correlation. [In choosing between two types of substituent constants, it is necessary to make use of substituents for which the two scales (say ct and rr, for example) are not themselves correlated, for otherwise both LFERs will be acceptable. ] The ct or o constants should be applicable to reactions that do not combine reaction sites and para substituents of the + and — type (push-pull systems capable of through resonance) for example, one would not expect ct" or o to provide good correlations for reactions of phenols or anilines substituted with nitro or cyano or for reactions of benzoic acids substituted with amino or methoxy. 

Based on the BOA theory, Barzoukas and Blanchard-Desce developed a two-state two-form model for the Pq of push-pull compounds [48]. The y o was expressed as a function of the newly defined parameter MIX, which is related to the degree of mixing between the neutral and zwitterionic resonance forms in the ground and excited state. This treatment has the advantage of conceptual simplicity and that it relies on a structural parameter that can be more easily used for other push pull molecular systems than polyenes. The evolution of y o observed with MIX is identical to that with BOA. The BOA theory was later also used to optimize the figure-of-merit of dyes for photorefractive applications [49, 50]. 

Fig. 4. Schematics of push-pull molecules for electro-optic and photorefractive applications...

In this contribution we discuss mm based on pp chromophores, a very interesting class of molecules for applications in molecular photonics and electronics. Push-pull chromophores are both polar and polarizable and this makes the role of intermolecular interactions particularly important. The toy model we propose for clusters of pp chromophores neglects intermolecular overlap, just accounting for classical electrostatic intermolecular interactions, and describes each pp chromophore based on a two state model. The two-state model for pp chromophores has been discussed and validated via an extensive comparison with the spectroscopic properties of several dyes in solution [74, 75, 90], The emerging picture is safe and led to the definition of a reliable set of molecular parameters for selected dyes. This analysis then offers valuable information to be inserted into models for clusters of interacting chromophores, in a the bottom-up modeling strategy that was nicely exemplified in Ref. [90]. 

Innocenzi, P., Brusatin, G., Abbotto, A., Beverina, L., Pagani, G.A., Casalboni, M., Sarcinelli, F., Pizzoferrato, R. Entrapping of push-pull zwitterionic chromophores in hybrid matrices for photonic applications. Journal of Sol-Gel Science and Technology, 26, 967-970 (2003)... 

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