Abstract

Substituted linear polyenes are interesting compounds presenting large χ⁽³⁾ values because of the quasi-one dimensional nature of the π electron system and its delocalization along the polyenic chain. Until now all χ⁽³⁾ values were obtained for ground-state molecules. Recently it was pointed out¹ that strong enhancement of χ⁽³⁾ values could be expected in the excited states. Indeed, electronic delocalisation can be larger in the excited states than in the ground state in these compounds. This paper is concerned with the non-linear properties of the excited states of a series of diphenyl-polyene derivatives with increasing polyenic chain length (from one to four C=C double bond). In order to investigate χ⁽³⁾ properties of these compounds we used two kinds of experiments, namely degenerate four wave mixing (DFWM) and the optical Kerr effect (OKE). Different combinations of one dye laser pulse (600 nm and 700-fs duration) and its second harmonic (300-nm) were used. The UV pulse is used to create the excited-state population and can be delayed (relative to the 600-nm pulse) to investigate dynamic properties. The yellow pulse at 600 nm creates the anisotropic properties inside the sample. For OKE experiments the transmission of the setup is measured by collecting a transmitted continuum of light extending from 360 nm to 900 nm. In this case it is possible to observe the spectral dependence of the created anisotropy at different wavelengths.

© 1994 IEEE