Optical Properties in Solution

There have been some attempts to compute nonlinear optical properties in solution. These studies have shown that very small variations in the solvent cavity can give very large deviations in the computed hyperpolarizability. The valence bond charge transfer (VB-CT) method created by Goddard and coworkers has had some success in reproducing solvent effect trends and polymer results (the VB-CT-S and VB-CTE forms, respectively). 

The nonlinear optical properties in solution of selected functionalized PDAs, described herein, have also been evaluated by means of the z-scan technique. Off resonance studies (at 705 nm) show that nonlinear refraction is only comparable to that of the solvent for these dilute solutions, but that nonlinear absorption, characterized by p values, varies significantly, with the nature of the side-chains. O It can be inferred that if bulk films of these PDAs possess suitable nonresonant nonlinear refractive properties for optical devices, modification of side-chain structure can reduce the magnitude of undesirable two photon absorption. 

Dialkyl-PPEs 3 have been examined by the Bunz group.Their optical properties in solution and in the solid state are well-understood (Table 12, entry... 

Hilberer, A., et al. 1997. Poly(phenylenevinylene)-type conjugated alternating copolymers Synthesis and optical properties in solution. Macromol Chem Phys 198 2211. 

V. N. Tsvetkov, Rigid-Chain Polymers Hydrodynamic and Optical Properties in Solution Consultants Bureau, New York, 1989. 

The optical properties in solution and interactions with salts of polymer and model compound have been investigated and are reported in more detail by Dr M. Vert. 

More recently, (+)-l,2-diethylpropane, a model diether for the repeating unit of propylene oxide, was prepared by Furukawa et al [101,102] and its behavior in solution regarding ORD and NMR was compared with those of the polymer. It was found that the model compound and polypropylene oxide show essentially the same optical properties in solution. By using the Brewster model of optical activity, it was concluded that the sol-vatation of the polymer may well modify the polarizability of the OA species so as to cause changes in the order of the polarizability of four atoms directly attached to the asymmetric carbon. 

To sum up, while there is too little information available to draw any firm conclusions, it appears that films deposited from most thiourea baths are weakly absorbing in the near-IR region and that films deposited from thiosulphate solutions (which are mildly acidic) may possess different optical properties in general than those deposited from (alkaline) thiourea baths. In this respect, and if this difference is real, it would be interesting to deposit PbS from thioacetamide baths, which can be both acidic and alkaline. 

Use of the optically resolved complex leads to the optically active polymer, but this property, which arises from the helical chain structure, is found only in the swollen polymer and is easily lost in toluene or dichloroacetic acid solution 144). The polymerization occurs with a high degree of enantioface selection, and the model for the product backbone is indeed chiral. However, because of the presence of a mirror, plane in the polymer chain (effects of chain termini neglected), the product does not have chiral properties in solution. 

The membranes of the rod discs are -60% protein and 40% lipid (Table 8-3). About 80% of the protein is rhodopsin (visual purple), a lipoprotein that is insoluble in water but soluble in detergent solutions. Digito-nin is widely used to disperse rhodopsin molecules because it causes no change in optical properties. In addition to rhodopsin, in the outer segment discs of frog retinal rods, there are -65 molecules of phospholipid and smaller amounts of other materials for each molecule of rhodopsin (Table 8-3). The cone cells have a similar architecture but have a different shape and contain different light receptors. The receptors in the cones are present in deep indentations of the plasma membrane rather than in discs within the cytoplasm. 

Liquid-crystalline solutions and melts of cellulosic polymers are often colored due to the selective reflection of visible fight, originating from the cholesteric helical periodicity. As a typical example, hydroxypropyl cellulose (HPC) is known to exhibit this optical property in aqueous solutions at polymer concentrations of 50-70 wt%. The aqueous solution system is also known to show an LCST-type of phase diagram and therefore becomes turbid at an elevated temperature [184]. 

Many of the different susceptibilities in Equations (2.165)-(2.167) correspond to important experiments in linear and nonlinear optics. x<(>> describes a possible zero-order (permanent) polarization of the medium j(1)(0 0) is the first-order static susceptibility which is related to the permittivity at zero frequency, e(0), while ft> o>) is the linear optical susceptibility related to the refractive index n" at frequency to. Turning to nonlinear effects, the Pockels susceptibility j(2)(- to, 0) and the Kerr susceptibility X(3 —to to, 0,0) describe the change of the refractive index induced by an externally applied static field. The susceptibility j(2)(—2to to, to) describes frequency doubling usually called second harmonic generation (SHG) and j(3)(-2 to, to, 0) describes the influence of an external field on the SHG process which is of great importance for the characterization of second-order NLO properties in solution in electric field second harmonic generation (EFISHG). 

Figure 3.106. Chemical structure and UV absorption spectra of organic compounds showing optical limiting properties in solution. (From Ref. [529] with permission of the American Institute of Physics.)...

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