Polarized modes, displays

It is obvious from Figure 3.9 that both the frequency and bandwidth of the C=0 stretching mode displays remarkable sensitivity to the polarity and the H-bonding ability of the solvent. The frequency downshift and slight bandwidth broadening observed when changing the solvent from cyclohexane to MeCN is due to the nonspecific electrostatic solvent-solute interaction affected mainly by the solvent... 

Figure 4 Femtosecond 2D-IR vibrational echo spectrum of (acac)Rh(CO)2 in hexane in the i (CO) region. This is the spectrum obtained when the train of four IR pulses used in the experiment had parallel polarizations. It displays a correlation of vibrational frequencies during two experimentally controlled time periods and the data are plotted as a function of frequencies excited during the evolution (cci) and detection (1 3) periods. Off-diagonal peaks represent anharmonic coupling between the i (CO) modes. (Adapted by permission of the American Institute of Physics from J. Chem. Phys. 2001, 115, 10814-10828.)...

Transmissive mode displays in which orientation effects are utilized, are located between two crossed polarizer films (Fig. 13c). The illuminating source can mostly be situated immediately behind the liquid crystal display. Colored liquid crystal displays which, for example, exploit the DAP effect (Deformation of Aligned Phases), must be illuminated by collimated light to avoid dependence of the color on the viewing angle. Moreover the front electrode must be a scattering disc. Collimated illumination is not required for color displays with homogeneously oriented liquid crystal layers, for example when the depolarization effect is used. 

In contrast, the a-peroxy lactones, also members of the dioxetane family, display a higher reactivity toward nucleophiles, in view of the inherent polarization of the peroxide bond by the carbonyl functionality. Consequently, the nucleophilic attack is expected to take place at the more sterically hindered but more electrophilic alkoxy-type oxygen atom of the peroxide bond. A recent detailed study of the oxidation of various di-, tri-and tetrasubstituted alkenes 6 with dimethyl a-peroxy lactone (7) revealed, however, much complexity, as illustrated in Scheme 7 for R = CH3, since cycloaddition (8), ene-reaction (9 and 10) and epoxidation (11) products were observed. In the presence of methanol, additionally the trapping products 12 and 13 were obtained, at the expense of the polyester 14. The preferred reaction mode is a sensitive function of the steric demand imposed by the attacking alkene nucleophile. 

---