Structure/property relationships for molecular second‐order nonlinear optics

Using a two‐state model, it was recently shown that there is an optimal combination of donor and acceptor strengths for a given bridge that will maximize the first molecular electronic hyperpolarizability (β). Implementation of this strategy relies on the realization that molecules with strongly aromatic end groups will not have the correct balance of two limiting charge transfer resonance forms in the ground state to achieve the degree of bond alternation required to optimize the molecular hyperpolarizability. Electric field induced second harmonic generation studies on organic molecules with various bridge structures support our hypothesis.