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Third-order harmonic generation has been measured on highly oriented polydiacetylene (PDA) films prepared by the vacuum deposition method. Experimental values of the third-order electric susceptibility χ(3) measured for pumping laser polarized parallel to the polymer chain show a sharp three-photon resonance to the 1Bu exciton in PDA. Potential usefulness of these highly oriented PDA evaporated films in nonlinear optical applications is suggested.

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Exciton self-trapping and formation of diradical intermediates in 5,7-dodecadiyne-1,12-diol bis[phenyl carbamate] (TCDU) crystals at low temperaturesThe crystal structure of the as-prepared form ofpoly(S,7-dodecadiyne-l,12-diyl-bisphenylurethane), customarily called TCDU, has been reexamined by an x-ray analysis. Bond lengths of the conjugated polymer backbone chain presently determined indicate that the structure of the as-prepared form of TCDU crystal is more close to that predicted for the acetylenic structure than the hitherto presumed butatrienic one.