Recent advances in nonlinear spectroscopy and nonlinear optical materials

High-symmetry, π-electron, ladder oligomers and polymers, theoretically capable of supporting polarons and bipolarons, have been synthesized and examined by degenerate four wave mixing experiments employing picosecond and femtosecond pulses. The results of these experiments have been analyzed employing density matrix theory with explicit consideration of radiation field-matter interactions and of molecular relaxation processes consisting of (1) electron-hole recombination/exciton decay, (2) structural relaxation to gap states, and (3) decay of the populations of gap states