Influence of the Polymeric Matrix on the NLO Molecular Response in Guest-Host Materials
n the presented work the linear and nonlinear optical susceptibilities of poled guest-host polymer systems are calculated. Two different systems were investigated, both considering poly(methyl methacrylate) (PMMA) matrix and derivatives of the pyrazolo-quinilines (PAQ). As a tool for the quantum chemical calculations, the molecular dynamic simulations of the considered systems were performed. Using structures simulated by molecular dynamics, the permanent local field, applied to compute polarizability a and b of the PAQ chromophores, was calculated. The electrical properties of the considered chromophores were computed with density functional theory (DFT). The permanent local fields in the bulk are small; however, their effects on the first hyperpolarizabilities are comparably large. Refractive indices and second-order susceptibilities corresponding to second harmonic generation (SHG) are calculated using a local field approach. The system PAQ1/PMMA can be well-described by the point-dipole approach, whereas for PAQ2/PMMA only distributed molecular response models can yield reasonable results.