Polarisability anisotropy

Molecular polarisability anisotropy and high order multipoles... 

Fig. 5 Excitation polarisation anisotropy histograms for more than 200 single PFO chains, a Histogram for the ( > phase, b Histogram for chains in the glassy phase subjected (shaded black bars) or not subjected (filled blue bars) to the vapour swelling treatment. Adapted from [28]...

Fig. 9 a Correlation between transition linewidth and polarisation anisotropy in -phase PFO for a total of 80 3-phase single molecules (circles), excited at412nm. The diamonds indicate an average over steps of 0.1 in polarisation anisotropy. The errors in the determination of linewidth and anisotropy are 0.25 meV and 0.03, respectively, b Scatter plot of linewidth and 0-0 transition energy, showing that the transition energy of the fi phase does not correlate with the linewidth. Adapted from [28]... 

Refractive index studies allow measurements of the birefringence, but also of the polarisability. The mean polarisability (a) can be determined using an isotropic liquid solution, whereas the polarisability anisotropy (Aa) is measured in the mesophase. Polarisability studies have been made on palladium, platinum, iridium and silver metallomesogens, and show a higher polarisability for the metal complexes than for their parent ligands. ... 

As discussed in Section 4.1, the specific adsorption of the ionic porphyrins at the liquid/liquid interface manifests itself by changes in the distribution of ions at the interface as well as in the interfacial tension. However, these two parameters do not provide direct information on the organisation of the adsorbed species in terms of lateral interactions and average molecular orientation. These aspects will be reviewed in Section 4.2 based on SHG and photocurrent Ught polarisation anisotropy studies of metalloporphyrins at the polarised water/IX2E interface. 

Accordingly, it was a long held theory that the nematic phase, for example, was generated because of the anisotropy of the polarisabihty restrlting from the conju ted core unit and that the higher the polarisability anisotropy the higher the nematic phase stability (Tj. j)... 

EQNS (1), (2) and (3) are commonly used as the basis of the molecular interpretation of the static permittivities measured as a function of temperature (e.g. [6,12-15,20,21,28-30,36,37]) and/or pressure [30,38]. Recently, quite successful predictions of anisotropic optical and dielectric constants from molecular modelling calculations were achieved with the aid of the Maier-Meier theory [39,40]. It seems worthwhile, therefore, to analyse these equations in order to point out the weak and strong points of the theory. EQN (3) is the most convenient for this purpose (both components of the permittivity are discussed by Jadzyn et al in a recent paper [41]). The parameters N, F and h in the Maier-Meier equations vary little with temperature. Therefore, the contribution from the polarisability anisotropy Aa to A8 varies with temperature in the same way as the order parameter S, whereas that connected with the orientation polarisation varies like S/T. Especially interesting seems to be the case of constant temperature discussed in [38] where As was measured as a function of pressure, p. The discussion of the measured permittivities, Sj and the anisotropy As as a function of the order parameter S obtained from the independent experiment seems to be the best way of verifying the assumptions on which the theory is based. 

The theoiy for the scattering changes cannot be expressed as simply as for the foregoing methods. Equations have been published for rigid rods and discs and for flexible and frrKen coils which are either polar or exhibit a polarisability anisotropy. For the rigid molecuks, at low degrees of orientation. 

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