Substituent-dependence of the optical nonlinearities in poly(2,5-dialkoxy-p-phenylenevinylene) polymers investigated by the Z-scan technique

We investigated the relationship existing between the third-order nonlinear optical (NLO) properties and the chemical structure of some poly(2,5-dialkoxy-1,4-phenylenevinylene) polymers. The latter have similar degrees of polymerization and polydispersity indexes and differ only for the structure of the side groups in the 2,5 positions of the phenylene rings. The two-photon absorption coefficient and the nonlinear refractive index have been measured using the picosecond Z-scan technique. Experimental results show that all the investigated organic molecules exhibit a small Im chi ((3)) and a large, negative Re chi ((3)) at lambda = 1064 nm. A considerable dependence of the third-order NLO properties on the steric effect of the substituents has been observed. (C) 2001 Elsevier Science B.V. All rights reserved.