Synthesis and second-order nonlinear optical properties of cross-linked polyurethanes with hemicyanine-type chromophores

Abstract

The crosslinked polyurethanes with three different bonding sites were prepared by the reaction of poly[(phenylisocyanate)-co-formaldehyde], which has one cross linking site located at every phenylene moiety, and hydroxy-functionalized chromophores. To obtain the high nonlinear optical activity of polymers, hemicyanine-type chromophore with high molecular hyperpolarizability (beta) was introduced into the polyurethane structure. The chi((2)) values of the resulting poled and cured polymers ranged between 16.8 pm/V similar to 37.4 pm/V at 1.064 mu m wavelength. According to thermal stability studies of second harmonic generation activity on PU-VP, it was found that the decay of chi((2)) value was minimized due to the lattice hardening of polyurethane matrix with three bonding sites.