Molecular shape change

Figure 1.15 Comparison of molecular shape change, two-dimensional branch cell amplification surface branch cells, surface groups (Z) and molecular weights as function of generation G= 0-6...

The contribution of photo-induced nonpolar orientation through even order parameters (see Equation 8A.9 in the appendix, page 286) to the effects observed in the EFISH decrease is negligible. The same decrease is observed for a TE- or TM-polarized probe regardless of the pump polarization (not shown). The photochemically induced molecular shape change of the NLO dye blows out the strong optical field driven anharmonic movement of the... 

The photochemical reduction of y is further rationalized by a theoretical model that neglects photo-orientation effects to EFISH and assumes that y of the chromophore decreases upon trans to cis molecular shape change. The model predicts an EFISH intensity at the photostationary state, which varies hyperbolically relative to the irradiating light intensity. Indeed, hyperbolic functions were adjusted to the experimental data showing the variation of the SH intensity at the steady state of the irradiation versus the irradiation intensity for both PI-1 and PI-2 (not shown). This finding demonstrates that the azo chromophores in PI-1 and PI-2 behave consistently with the model, and validates the concept of the reversible rapid photochemical erase of y oi these isomerizable NLO dyes. 

One may formally decompose the molecular shape changes associated with an electronic excitation into separate steps as follows. 

Shape in chemistry appears on many levels. The shapes of crystals, the shapes of titration curves, the shapes of spectral lines, the shapes of potential energy functions or the multidimensional shapes of potential energy hypersurfaces are some examples. However, few chemists would dispute that the most important shape problem of chemistry is that of the three-dimensional shapes of molecules. The study of molecular shape and molecular shape changes is fundamental to our understanding of chemical properties and reactions. 

G. A. Arteca and P. G. Mezey, /. Phys. Chem., 93, 4746 (1989). Molecular Similarity and Molecular Shape Changes Along Reaction Paths A Topological Analysis and Consequences on the Hammond Postulate. 

SmC host PhB. The plot of Pg as a function of temperature at both states showed that no appreciable shift was found in the Curie point, i.e. no destabihzation effect caused by molecular shape change from the photoisomerization observed. The Pg of different concentrations of 32 in PhB was found to increase upon irradiation at 532 nm. As shown in Fig. 5.26, irradiation of a 1.9 mol % mixture resulted in an almost fourfold increase, however, the magnitude decreased upon increasing dopant concentration, which might be due to the suppression of trans-cis photoisomerization by aggregate formation. 

With the supermolecular architectures described in this section, it is difficult to continue adding more mesogens to the central scaffold in order to examine how the overall molecular shape changes, and thereby affects mesophase... 

Figure 3 Adendrimer series with core multiplicity (Nc = 3) and branch-cell multiplicity (Afc = 2) illustrating molecular shape changes, surface branch cells, surface Z-groups, and molecular weights as a function of generation.

Polyelectrolytes literally possess dissociated groups on the polymer chain and conformation is strongly influenced by the state of the electric charge. Thus, the molecular shape changes drastically by changing pH,... 

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