Importance of intermolecular interactions in the nonlinear optical properties of poled polymers

A series of phenylbithiophene stilbenes and phenyltetraenes were synthesized and their first-order molecular hyperpolarizabilities determined. Optical nonlinearities up to mu beta(o)=9300x10(-69) C m(5)/V were measured at 1907 nm. We show that intermolecular interactions have a large influence on the optical nonlinearity of the molecules in solution and in guest-host polymers with polymethylmethacrylate and polyquinoline as the host. We propose the use of a bulky donor group and a side chain perpendicular to the molecule's conjugate bridge to reduce aggregation. Electro-optic coefficients as high as r(33)=30 pm/V at 1.55 mu m in polymethylmethacrylate with 25 wt % chromophore loading were measured. (C) 2000 American Institute of Physics. [S0003-6951(00)02611-5].