Crystal dipole

Interaction of incident electrons with the electrostatic potential (ESP) gives the possibility to reconstmct the potential from transmission electron diffraction (ED) experiments. ESP and the electron density determine all physical properties of crystals (e.g. energy of electrostatic interaction, characteristics of the electrostatic field in crystals, dipole, quadmple and other momentum of nuclear, diamagnetic susceptibility. 

Molecular weight 124.068 Melting point 110 °C White lamellar crystals Dipole moment 3.46 D... 

Peptides represent yet another family of intervening materials that provide a probe for conformational effects. Because peptides can aggregate as helices or as sheets, they produce a macromolecular order comparable to that of liquid crystals. Dipole effects in helical peptides are additive, so that a macroscopic dipole from the C- to the N-end of the peptide (or vice versa) can enhance or oppose the pulsed PET. 

The polarization properties of single-molecule fluorescence excitation spectra have been explored and utilized to detennine botli tlie molecular transition dipole moment orientation and tlie deptli of single pentacene molecules in a /7-teriDhenyl crystal, taking into account tlie rotation of tlie polarization of tlie excitation light by tlie birefringent... 

Chiral Smectic. In much the same way as a chiral compound forms the chiral nematic phase instead of the nematic phase, a compound with a chiral center forms a chiral smectic C phase rather than a smectic C phase. In a chiral smectic CHquid crystal, the angle the director is tilted away from the normal to the layers is constant, but the direction of the tilt rotates around the layer normal in going from one layer to the next. This is shown in Figure 10. The distance over which the director rotates completely around the layer normal is called the pitch, and can be as small as 250 nm and as large as desired. If the molecule contains a permanent dipole moment transverse to the long molecular axis, then the chiral smectic phase is ferroelectric. Therefore a device utilizing this phase can be intrinsically bistable, paving the way for important appHcations. 

In order for dipole—dipole and dipole-iaduced dipole iateractioas to be effective, the molecule must coataia polar groups and/or be highly polarizable. Ease of electronic distortion is favored by the presence of aromatic groups and double or triple bonds. These groups frequently are found ia the molecular stmcture of Hquid crystal compouads. The most common nematogenic and smectogenic molecules are of the type shown ia Table 2. 

Fig. 3. Alignment of amide dipoles in polyamide crystals (a) for a two-dimensional array of an odd nylon, nylon-7, (b) for a one-dimensional array of an odd—odd nylon, nylon-5,7 (c) for one-dimensional arrays of polyamides containing even segments an even nylon, nylon-6 an even—even nylon, nylon-6,6 ...

---