Modeling of epoxy oligomers with nonlinear optical chromophores in the main chain: Molecular dynamics and quantum chemical study

The Molecular Dynamics simulations in chloroform at room temperature of the monomer and dimer of the molecular system based on bisphenol-A diglycidyl ether with a p-nitroaniline (PNA) chromophore attached to the bearing chain is performed. The starting conformations for the simulation were obtained by the conformational search in the framework of Monte Carlo method with MMFF94 force field. The monomer was shown to represent an adequate model for the corresponding oligomer unit. The analysis of the torsion angles values along the bearing chain of dimer demonstrates the availability of flexible fragments, thus giving promise for efficient orientation of chromophore groups in a chosen polymer matrix when the electric field is switched on. The polarizability and first hyperpolarizability of the studied systems are calculated by TDHF/AM1. The values of β∥ increase by nearly 50% when passing from the monomer to the dimer. The nonempirical calculation of β, performed for the monomer, examines the obtained trends and exhibits significant enhancement of the first hyperpolarizability in chloroform approximately by a factor of 3 with respect to the gas phase value. © 2007 Wiley Periodicals, Inc.