Designing effective nonlinear optical (NLO) materials with chiral substituents

The experimental strategies and theoretical understanding in transforming molecular conformations with good SHG response functions into polymers with the help of chiral groups are discussed. Chirality plays an important role in designing new types of stable second-order NLO materials. The presence of chiral molecules in the main chain of the polymer introduces acentric conformations and thereby increases the SHG efficiency. On the other hand, for strong donor and acceptor groups between a pi-bridge, large SHG coefficients can be realized at the molecular scale. Chiral molecules are noncentrosymmetric with a nonvanishing electric-dipole-allowed second-order response, which persists in bulk samples also. On the other hand, contributions of magnetic-dipole interactions, which can be strong in chiral materials, allow second-order processes in centrosymmetric materials. Also the polymers incorporated with chiral molecules showed higher response than the standard MNA. This could be due to the chiral component contribution to the electric and magnetic-dipole tensor.