Ab Initio Design of Two-Photon Absorbing Materials

Abstract

AbstractTwo-photon absorbing materials such as conjugated polyenes show promise as nonlinear optical materials. Prediction of two-photon absorption frequencies and cross-sections has been limited by the high level of ab initio calculations that must be carried out in order to accurately calculate excited state energies and transition dipole moments, by the size of many of the compounds of interest, and by the difficulty of handling condensed phase effects in the calculations. We have carried out geometry optimizations at the multi-configurational selfconsistent field level on a small polyene, hexatriene, both in the gas-phase and in solution, with the solvent effects being modeled by the effective fragment potential. The excited-state energies have been calculated by the multiconfigurational quasidegenerate perturbation theory. Transition dipole moment calculations have also been carried out, from which the two-photon absorption cross-section can be estimated. The results indicate that just one or two solvent molecules can have a large effect on the nonlinear optical properties of two-photon absorbing materials.