Conformational dependence and femtosecond response of the third-order nonlinearity in retinal derivatives

Summary form only given. The nonlinear optical properties of organic materials have been thoroughly studied with views to the basic understanding of its physical origin as well as to their application in photonic devices. It is the /spl pi/-electron delocalization in organic molecules that leads to high molecular hyperpolarizabilities and large nonlinear susceptibilities. Retinal, a molecular structure related to vitamin A, and its derivatives belong to a family of molecules that plays a prevalent role in photobiological processes. For instance, the primary event of vision mechanism in animals is associated to the cis to trans isomerization of the retinal molecule. Tote and coworkers (1994) have predicted that this conformational change should be accompanied by a noticeable change in the hyperpolarizability of the molecules since the more linear character of the trans conformation should favor the delocalization of the /spl pi/-electrons in the conjugated system. We used the Z-scan technique to determine the nonlinear refractive index and the nonlinear absorption coefficient.