Preparation and nonlinear optics of monodisperse oligo(1,4-phenyleneethynylene)s

Oligo(1,4-phenyleneethynylene)s 1a-e, with solubilizing propoxy side chains , were prepared by use of Hagihara-Sonogashira coupling reactions. The synt hetic strategy was based on a building block system and on the use of trime thylsilyl and triisopropylsilyl protecting groups that could be cleaved sel ectively. The extension of the conjugation with an increasing number of rep eat units provokes a bathochromic shift of the long wavelength absorption a nd a superlinear increase of the second hyperpolarizability \ gamma \. The corresponding third harmonic generation (THG) measurements were performed u sing polystyrene matrices and variable laser wavelengths. We conclude that the conjugation length is much larger than 5 repeat units.