Polyenes, conjugated, Amax values

A third access to soluble polyenes lies in the ROMP of cyclooctatetraene (COT) derivatives. COTs are readily polymerized by W- and Mo-based Schrock carbenes to yield substituted polyenes (Scheme 36). As evidenced by UV—Vis spectroscopy, these materials which are synthesized in a predominately cis form are highly conjugated with values for Amax of up to 538 nm (R = />octadecyl). Thermal cis—trans isomerization is possible and may be monitored via UV— Vis spectroscopy. The resulting predominately all-trans polymers show values for Xmax of up to 634 nm (R = neopentyl). Upon doping of these materials with iodine, conductivities of up to 50 S/m may be achieved.Trimethylsilyl-substituted COT forms transparent polymers, which may be casted onto n-doped silicon (n-Si). Upon treatment with iodine, surface barrier solar cells may be prepared. Soluble,... 

Table 11.2—Displacement of absorption maximum for a family of conjugated polyenes. Values of Amax for a family of disubstituted conjugated polyenes with differing numbers of conjugated double bonds. The general structure is given on the right.

The intensity of the DFWM signal for the poly(l,6-heptadiyne)s increased linearly with intensity of the incident beam, as shown in Figure 10. From the direct comparison between the intercepts of the V axis of the polymers and the carbon disulfide reference. the values of the polymers were obtained. And also, as the concentration of the polymer solution was increased, the values of the polymers were increased (Figure 11). The third-order nonlinear optical properties were enhanced with an increase in the bulk of the substituents at the 4-position, which is in accord with the bathochromic shift of Amax in the UV—vis spectra. From these results, it was concluded that the incorporation of bulky substituents into the 4-position of 1,6-heptadiynes enforces the TT-conjugated polyene into the more planar conformation. resulting in a red shift and the increment of the values of the polymers. Recently, Schrock... 

The following examples show how the Woodward-Fieser rules predict values of Amax variety of conjugated ketones and aldehydes. Notice that the molar absorp-tivities (s) for these transitions are quite large (>5000), as we also observed for tt — tt transitions in conjugated dienes and polyenes. 

---