Salient Results Third Order NLO Effects

Some of the first third order NLO studies of CPs were carried out on the poly(di-acetylenes) (P(DiAc)). One of the first such studies, on P(DiAc)-toluene sulfonate (PTS) single crystals, carried out by Sauteret et al. [502], revealed third order bulk NLO susceptibilities x fzzzz) polymer chain axis) of 1.6 X 10 ° esu at 2.62 pm and 8.5 X 10 ° esu at 1.89 pm. These values have as yet been exceeded only by one study, that of Drury on oriented Durham P(Ac) [503], in which a value for x zzzz (Z= polymer chain axis) of 10 esu at 1.9 pm. However, this value of the susceptibility was inferred from THG data somewhat indirectly. Dennis et al. [504] reported off-resonant x xyyx values of 7 X 10 esu for solutions of various P(DiAc), extrapolated to pure substance and determined via DFWM at 532 nm. 

Sinclair et al. [505] studied both P(Ac) and P(DiAc)-4BCMU. Their THG measurements on oriented, trans-P(Ac) parallel to the fiber direction at an energy of 1.17 eV yielded a value of X xxxx of ca. 4 X 10 esu, more than 15 times larger than the corresponding measurement on the cis-isomer. Their study on the P(DiAc) yielded a nonlinear refractive index (n which was negative, with a value of 10 (MW/cm ) with a decay time for this nonlinearity of ca. 2.5 ps. Chollet et al. [506] studied the blue and red forms of several P(DiAc) films via THG, and observed two and three photon resonances, with X xxxx of ca. 5 X 10 esu at ca. 2 pm, Kanetake et al. [507] measured THG on highly oriented, urethane-based P(DiAc) films, prepared by vacuum deposition, at a wavelength of 1.9 pm. They found that for a pump direction parallel to the polymer chain, a three-photon resonance to the exciton, was observed, with a x of 3.8 X 10 esu (vs. 0.2 X 10 ° esu for the perpendicular direction). Their frequency-dispersive measurements 

The other common CP classes, such as the P(T)s and the P(Py)s, have also been the subject of much study. The Prasad group reported bulk third-order susceptibilities, in L-B films of undoped P(3-dodecyl thiophene) at 1.06 /tm of ca. 10 esu [287] In a subsequent study [509], the same group found off-resonant (at 620 nm) values of determined via DFWM for recast films of this partially soluble 

Rigid ladder polymers of the P(PV) type were studied recently by Samoc et al. [515] in chloroform solution. Fig. 12-29 summarizes some of their data. 

Measurements of three NLO parameters on urethane-derivative poly(diacetylene) films. After Kanetake et al. [507], reproduced with permission. 

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